JIT: support SSA-aware PHI jump threading - #126812

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JIT: support SSA-aware PHI jump threading#126812
AndyAyersMS merged 2 commits into
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Teach redundant branch elimination to keep jump threading through PHI- based blocks when the PHI uses can be fully accounted for in the block and its immediate successors. Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative, and add focused regression coverage for the new PHI-based cases.

Fixes#126703 (not quite, yet)

@AndyAyersMS
JIT: support SSA-aware PHI jump threading
644b5f7
Teach redundant branch elimination to keep jump threading through PHI-
based blocks when the PHI uses can be fully accounted for in the block
and its immediate successors. Rewrite the affected successor SSA/VN uses,
keep dominating-block threading conservative, and add focused regression
coverage for the new PHI-based cases.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI review requested due to automatic review settings April 12, 2026 20:29
@github-actionsgithub-actionsBot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Apr 12, 2026
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Pull request overview

This PR extends CoreCLR JIT redundant branch optimization (jump threading) to support PHI-based threading when PHI definitions have non-local uses, by accounting for those uses within the threaded block and its immediate successors and rewriting successor SSA/VN uses accordingly. It also adds a focused JIT regression test to cover the new PHI-based scenario.

Changes:

  • Add tracking of PHI SSA uses in the candidate block/successors and rewrite successor SSA/VN uses when threading bypasses the PHI block.
  • Refine jump-thread eligibility checking to return a richer classification (including “needs PHI use resolution”).
  • Add a new JIT test case (JumpThreadPhi) to validate the new behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file
FileDescription
src/coreclr/jit/redundantbranchopts.cppImplements PHI-use discovery and successor SSA/VN rewriting; updates jump-thread check flow.
src/coreclr/jit/compiler.hIntroduces JumpThreadCheckResult and declares new helper methods for PHI-use analysis/rewriting.
src/coreclr/jit/compmemkind.hAdds a dedicated allocator kind for redundant-branch/jump-threading data.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csAdds regression coverage for PHI-based jump threading through a PHI-producing pattern.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csprojAdds the test project definition consistent with existing tests in the folder.

Comment threadsrc/coreclr/jit/redundantbranchopts.cpp Outdated
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Follow-on to #126711.

If all the uses of a global phi in a jump-threading candidate block are in the block and its successors, we can (in most cases) allow jump threading and rewrite the successor uses to the appropriate new ssa def & vn.

We avoid cases where the successors already have PHIs or would need to have new PHIs. These seem somewhat rare.

@EgorBo PTAL
fyi @dotnet/jit-contrib

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Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Thanks for filing a fix for this!

@AndyAyersMS

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Thanks for filing a fix for this!

There are a couple of follow-ons coming that should let us actually fix #126703, but I think this is a good improvement on its own.

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Diffs

Linux x64 is probably most representative, other os/arch seem to be missing some collections.

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/ba-g dead-letter mac catalyst

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AndyAyersMS merged commit 578644c into dotnet:mainApr 13, 2026
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Revert "JIT: support SSA-aware PHI jump threading (#126812)"
108cc21
This reverts commit 578644c.
@MichalStrehovskyMichalStrehovsky mentioned this pull request Apr 15, 2026
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CopilotAI added a commit that referenced this pull request Apr 16, 2026
@mangod9
Cherry-pick JIT PHI jump threading (PR#126812) with targeted fix for…
cd43a53
… global PHI use bug (#126976)
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/1507ea1a-6b49-4f3d-977a-83f9c781da83
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
CopilotAI added a commit that referenced this pull request Apr 16, 2026
@mangod9
Revert "Cherry-pick JIT PHI jump threading (PR#126812) with targeted…
5a82a7d
… fix for global PHI use bug (#126976)"
This reverts commit cd43a53.
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
AndyAyersMS added a commit to AndyAyersMS/runtime that referenced this pull request Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
3af24b7
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
AndyAyersMS added a commit to AndyAyersMS/runtime that referenced this pull request Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
d86b525
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
@AndyAyersMSAndyAyersMS mentioned this pull request Apr 18, 2026
Merged
AndyAyersMS added a commit that referenced this pull request Apr 20, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading (#127103)
9850fe0
Teach redundant branch elimination to keep jump threading through
PHI-based blocks when the PHI uses can be fully accounted for in the
block and its immediate successors. Rewrite the affected successor
SSA/VN uses, keep dominating-block threading conservative, and add
focused regression coverage for the new PHI-based cases.
Fix included here that was not in #126812: ensure that field uses of
locals get the proper VN updates.
Fixes#126976.
@svicksvick mentioned this pull request Apr 21, 2026
Closed
@LoopedBard3LoopedBard3 mentioned this pull request Apr 23, 2026
Closed
@github-actionsgithub-actionsBot locked and limited conversation to collaborators May 14, 2026
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, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
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var __re = new RegExp('^' + "github\\.com" + '

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JIT: support SSA-aware PHI jump threading - #126812
Merged
AndyAyersMS merged 2 commits into
dotnet:mainfrom 
AndyAyersMS:RboSimpleSSAUpdates
Apr 13, 2026
Merged
JIT: support SSA-aware PHI jump threading#126812
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Teach redundant branch elimination to keep jump threading through PHI- based blocks when the PHI uses can be fully accounted for in the block and its immediate successors. Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative, and add focused regression coverage for the new PHI-based cases.
Fixes#126703 (not quite, yet)
@AndyAyersMS
JIT: support SSA-aware PHI jump threading
644b5f7
Teach redundant branch elimination to keep jump threading through PHI-
based blocks when the PHI uses can be fully accounted for in the block
and its immediate successors. Rewrite the affected successor SSA/VN uses,
keep dominating-block threading conservative, and add focused regression
coverage for the new PHI-based cases.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
April 12, 2026 20:29
@github-actionsgithub-actionsBot
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Pull request overview
This PR extends CoreCLR JIT redundant branch optimization (jump threading) to support PHI-based threading when PHI definitions have non-local uses, by accounting for those uses within the threaded block and its immediate successors and rewriting successor SSA/VN uses accordingly. It also adds a focused JIT regression test to cover the new PHI-based scenario.
Changes:
  • Add tracking of PHI SSA uses in the candidate block/successors and rewrite successor SSA/VN uses when threading bypasses the PHI block.
  • Refine jump-thread eligibility checking to return a richer classification (including “needs PHI use resolution”).
  • Add a new JIT test case (JumpThreadPhi) to validate the new behavior.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/jit/redundantbranchopts.cppImplements PHI-use discovery and successor SSA/VN rewriting; updates jump-thread check flow.
src/coreclr/jit/compiler.hIntroduces JumpThreadCheckResult and declares new helper methods for PHI-use analysis/rewriting.
src/coreclr/jit/compmemkind.hAdds a dedicated allocator kind for redundant-branch/jump-threading data.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csAdds regression coverage for PHI-based jump threading through a PHI-producing pattern.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csprojAdds the test project definition consistent with existing tests in the folder.
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Outdated

Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
@AndyAyersMS
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Apr 12, 2026

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Follow-on to #126711.
If all the uses of a global phi in a jump-threading candidate block are in the block and its successors, we can (in most cases) allow jump threading and rewrite the successor uses to the appropriate new ssa def & vn.
We avoid cases where the successors already have PHIs or would need to have new PHIs. These seem somewhat rare.
@EgorBo PTAL

fyi @dotnet/jit-contrib
@build-analysisbuild-analysisBot
mentioned this pull request
Apr 12, 2026

Closed

EgorBo
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Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Thanks for filing a fix for this!
@AndyAyersMS
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Thanks for filing a fix for this!
There are a couple of follow-ons coming that should let us actually fix #126703, but I think this is a good improvement on its own.
@AndyAyersMS
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Diffs
Linux x64 is probably most representative, other os/arch seem to be missing some collections.
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April 13, 2026 22:50
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/ba-g dead-letter mac catalyst
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Revert "JIT: support SSA-aware PHI jump threading (#126812)"
108cc21
This reverts commit 578644c.
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added a commit
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@mangod9
Cherry-pick JIT PHI jump threading (PR#126812) with targeted fix for…
cd43a53
… global PHI use bug (#126976)
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/1507ea1a-6b49-4f3d-977a-83f9c781da83
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
CopilotAI
added a commit
that referenced
this pull request
Apr 16, 2026
@mangod9
Revert "Cherry-pick JIT PHI jump threading (PR#126812) with targeted…
5a82a7d
… fix for global PHI use bug (#126976)"
This reverts commit cd43a53.
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
this pull request
Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
3af24b7
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
this pull request
Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
d86b525
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
@AndyAyersMSAndyAyersMS
mentioned this pull request
Apr 18, 2026
 Merged

AndyAyersMS added a commit
that referenced
this pull request
Apr 20, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading (#127103)
9850fe0
Teach redundant branch elimination to keep jump threading through
PHI-based blocks when the PHI uses can be fully accounted for in the
block and its immediate successors. Rewrite the affected successor
SSA/VN uses, keep dominating-block threading conservative, and add
focused regression coverage for the new PHI-based cases.
Fix included here that was not in #126812: ensure that field uses of
locals get the proper VN updates.
Fixes#126976.
@svicksvick
mentioned this pull request
Apr 21, 2026

Closed

@LoopedBard3LoopedBard3
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Apr 23, 2026

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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
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})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
JIT: support SSA-aware PHI jump threading - #126812
Merged
AndyAyersMS merged 2 commits into
dotnet:mainfrom 
AndyAyersMS:RboSimpleSSAUpdates
Apr 13, 2026
Merged
JIT: support SSA-aware PHI jump threading#126812
AndyAyersMS merged 2 commits into
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Apr 12, 2026•

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Teach redundant branch elimination to keep jump threading through PHI- based blocks when the PHI uses can be fully accounted for in the block and its immediate successors. Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative, and add focused regression coverage for the new PHI-based cases.
Fixes#126703 (not quite, yet)
@AndyAyersMS
JIT: support SSA-aware PHI jump threading
644b5f7
Teach redundant branch elimination to keep jump threading through PHI-
based blocks when the PHI uses can be fully accounted for in the block
and its immediate successors. Rewrite the affected successor SSA/VN uses,
keep dominating-block threading conservative, and add focused regression
coverage for the new PHI-based cases.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
April 12, 2026 20:29
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Pull request overview
This PR extends CoreCLR JIT redundant branch optimization (jump threading) to support PHI-based threading when PHI definitions have non-local uses, by accounting for those uses within the threaded block and its immediate successors and rewriting successor SSA/VN uses accordingly. It also adds a focused JIT regression test to cover the new PHI-based scenario.
Changes:
  • Add tracking of PHI SSA uses in the candidate block/successors and rewrite successor SSA/VN uses when threading bypasses the PHI block.
  • Refine jump-thread eligibility checking to return a richer classification (including “needs PHI use resolution”).
  • Add a new JIT test case (JumpThreadPhi) to validate the new behavior.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/jit/redundantbranchopts.cppImplements PHI-use discovery and successor SSA/VN rewriting; updates jump-thread check flow.
src/coreclr/jit/compiler.hIntroduces JumpThreadCheckResult and declares new helper methods for PHI-use analysis/rewriting.
src/coreclr/jit/compmemkind.hAdds a dedicated allocator kind for redundant-branch/jump-threading data.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csAdds regression coverage for PHI-based jump threading through a PHI-producing pattern.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csprojAdds the test project definition consistent with existing tests in the folder.
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Outdated

Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
@AndyAyersMS
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Follow-on to #126711.
If all the uses of a global phi in a jump-threading candidate block are in the block and its successors, we can (in most cases) allow jump threading and rewrite the successor uses to the appropriate new ssa def & vn.
We avoid cases where the successors already have PHIs or would need to have new PHIs. These seem somewhat rare.
@EgorBo PTAL

fyi @dotnet/jit-contrib
@build-analysisbuild-analysisBot
mentioned this pull request
Apr 12, 2026

Closed

EgorBo
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View reviewed changes
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Thanks for filing a fix for this!
@AndyAyersMS
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Thanks for filing a fix for this!
There are a couple of follow-ons coming that should let us actually fix #126703, but I think this is a good improvement on its own.
@AndyAyersMS
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Linux x64 is probably most representative, other os/arch seem to be missing some collections.
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Revert "JIT: support SSA-aware PHI jump threading (#126812)"
108cc21
This reverts commit 578644c.
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Cherry-pick JIT PHI jump threading (PR#126812) with targeted fix for…
cd43a53
… global PHI use bug (#126976)
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/1507ea1a-6b49-4f3d-977a-83f9c781da83
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
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added a commit
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@mangod9
Revert "Cherry-pick JIT PHI jump threading (PR#126812) with targeted…
5a82a7d
… fix for global PHI use bug (#126976)"
This reverts commit cd43a53.
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
AndyAyersMS added a commit
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Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
3af24b7
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
this pull request
Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
d86b525
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
@AndyAyersMSAndyAyersMS
mentioned this pull request
Apr 18, 2026
 Merged

AndyAyersMS added a commit
that referenced
this pull request
Apr 20, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading (#127103)
9850fe0
Teach redundant branch elimination to keep jump threading through
PHI-based blocks when the PHI uses can be fully accounted for in the
block and its immediate successors. Rewrite the affected successor
SSA/VN uses, keep dominating-block threading conservative, and add
focused regression coverage for the new PHI-based cases.
Fix included here that was not in #126812: ensure that field uses of
locals get the proper VN updates.
Fixes#126976.
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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JIT: support SSA-aware PHI jump threading - #126812
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AndyAyersMS:RboSimpleSSAUpdates
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JIT: support SSA-aware PHI jump threading#126812
AndyAyersMS merged 2 commits into
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Teach redundant branch elimination to keep jump threading through PHI- based blocks when the PHI uses can be fully accounted for in the block and its immediate successors. Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative, and add focused regression coverage for the new PHI-based cases.
Fixes#126703 (not quite, yet)
@AndyAyersMS
JIT: support SSA-aware PHI jump threading
644b5f7
Teach redundant branch elimination to keep jump threading through PHI-
based blocks when the PHI uses can be fully accounted for in the block
and its immediate successors. Rewrite the affected successor SSA/VN uses,
keep dominating-block threading conservative, and add focused regression
coverage for the new PHI-based cases.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
April 12, 2026 20:29
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Pull request overview
This PR extends CoreCLR JIT redundant branch optimization (jump threading) to support PHI-based threading when PHI definitions have non-local uses, by accounting for those uses within the threaded block and its immediate successors and rewriting successor SSA/VN uses accordingly. It also adds a focused JIT regression test to cover the new PHI-based scenario.
Changes:
  • Add tracking of PHI SSA uses in the candidate block/successors and rewrite successor SSA/VN uses when threading bypasses the PHI block.
  • Refine jump-thread eligibility checking to return a richer classification (including “needs PHI use resolution”).
  • Add a new JIT test case (JumpThreadPhi) to validate the new behavior.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/jit/redundantbranchopts.cppImplements PHI-use discovery and successor SSA/VN rewriting; updates jump-thread check flow.
src/coreclr/jit/compiler.hIntroduces JumpThreadCheckResult and declares new helper methods for PHI-use analysis/rewriting.
src/coreclr/jit/compmemkind.hAdds a dedicated allocator kind for redundant-branch/jump-threading data.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csAdds regression coverage for PHI-based jump threading through a PHI-producing pattern.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csprojAdds the test project definition consistent with existing tests in the folder.
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Outdated

Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Follow-on to #126711.
If all the uses of a global phi in a jump-threading candidate block are in the block and its successors, we can (in most cases) allow jump threading and rewrite the successor uses to the appropriate new ssa def & vn.
We avoid cases where the successors already have PHIs or would need to have new PHIs. These seem somewhat rare.
@EgorBo PTAL

fyi @dotnet/jit-contrib
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EgorBo
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Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Thanks for filing a fix for this!
@AndyAyersMS
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Thanks for filing a fix for this!
There are a couple of follow-ons coming that should let us actually fix #126703, but I think this is a good improvement on its own.
@AndyAyersMS
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Linux x64 is probably most representative, other os/arch seem to be missing some collections.
@AndyAyersMS
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April 13, 2026 22:50
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/ba-g dead-letter mac catalyst
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merged commit 578644c
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dotnet:mainApr 13, 2026

142 of 145 checks passed

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@MichalStrehovsky
Revert "JIT: support SSA-aware PHI jump threading (#126812)"
108cc21
This reverts commit 578644c.
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@mangod9
Cherry-pick JIT PHI jump threading (PR#126812) with targeted fix for…
cd43a53
… global PHI use bug (#126976)
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/1507ea1a-6b49-4f3d-977a-83f9c781da83
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
CopilotAI
added a commit
that referenced
this pull request
Apr 16, 2026
@mangod9
Revert "Cherry-pick JIT PHI jump threading (PR#126812) with targeted…
5a82a7d
… fix for global PHI use bug (#126976)"
This reverts commit cd43a53.
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
this pull request
Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
3af24b7
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
this pull request
Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
d86b525
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
@AndyAyersMSAndyAyersMS
mentioned this pull request
Apr 18, 2026
 Merged

AndyAyersMS added a commit
that referenced
this pull request
Apr 20, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading (#127103)
9850fe0
Teach redundant branch elimination to keep jump threading through
PHI-based blocks when the PHI uses can be fully accounted for in the
block and its immediate successors. Rewrite the affected successor
SSA/VN uses, keep dominating-block threading conservative, and add
focused regression coverage for the new PHI-based cases.
Fix included here that was not in #126812: ensure that field uses of
locals get the proper VN updates.
Fixes#126976.
@svicksvick
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Apr 21, 2026

Closed

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Apr 23, 2026

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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

Skip to content
JIT: support SSA-aware PHI jump threading - #126812
Merged
AndyAyersMS merged 2 commits into
dotnet:mainfrom 
AndyAyersMS:RboSimpleSSAUpdates
Apr 13, 2026
Merged
JIT: support SSA-aware PHI jump threading#126812
AndyAyersMS merged 2 commits into
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Apr 12, 2026•

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Teach redundant branch elimination to keep jump threading through PHI- based blocks when the PHI uses can be fully accounted for in the block and its immediate successors. Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative, and add focused regression coverage for the new PHI-based cases.
Fixes#126703 (not quite, yet)
@AndyAyersMS
JIT: support SSA-aware PHI jump threading
644b5f7
Teach redundant branch elimination to keep jump threading through PHI-
based blocks when the PHI uses can be fully accounted for in the block
and its immediate successors. Rewrite the affected successor SSA/VN uses,
keep dominating-block threading conservative, and add focused regression
coverage for the new PHI-based cases.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
April 12, 2026 20:29
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Pull request overview
This PR extends CoreCLR JIT redundant branch optimization (jump threading) to support PHI-based threading when PHI definitions have non-local uses, by accounting for those uses within the threaded block and its immediate successors and rewriting successor SSA/VN uses accordingly. It also adds a focused JIT regression test to cover the new PHI-based scenario.
Changes:
  • Add tracking of PHI SSA uses in the candidate block/successors and rewrite successor SSA/VN uses when threading bypasses the PHI block.
  • Refine jump-thread eligibility checking to return a richer classification (including “needs PHI use resolution”).
  • Add a new JIT test case (JumpThreadPhi) to validate the new behavior.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/jit/redundantbranchopts.cppImplements PHI-use discovery and successor SSA/VN rewriting; updates jump-thread check flow.
src/coreclr/jit/compiler.hIntroduces JumpThreadCheckResult and declares new helper methods for PHI-use analysis/rewriting.
src/coreclr/jit/compmemkind.hAdds a dedicated allocator kind for redundant-branch/jump-threading data.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csAdds regression coverage for PHI-based jump threading through a PHI-producing pattern.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csprojAdds the test project definition consistent with existing tests in the folder.
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Outdated

Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
@AndyAyersMS
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Follow-on to #126711.
If all the uses of a global phi in a jump-threading candidate block are in the block and its successors, we can (in most cases) allow jump threading and rewrite the successor uses to the appropriate new ssa def & vn.
We avoid cases where the successors already have PHIs or would need to have new PHIs. These seem somewhat rare.
@EgorBo PTAL

fyi @dotnet/jit-contrib
@build-analysisbuild-analysisBot
mentioned this pull request
Apr 12, 2026

Closed

EgorBo
EgorBo
reviewed
Apr 13, 2026
View reviewed changes
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Thanks for filing a fix for this!
@AndyAyersMS
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Apr 13, 2026

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Thanks for filing a fix for this!
There are a couple of follow-ons coming that should let us actually fix #126703, but I think this is a good improvement on its own.
@AndyAyersMS
AndyAyersMS
commented
Apr 13, 2026

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Diffs
Linux x64 is probably most representative, other os/arch seem to be missing some collections.
@AndyAyersMS
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enabled auto-merge (squash)
April 13, 2026 22:50
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/ba-g dead-letter mac catalyst
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merged commit 578644c
into
dotnet:mainApr 13, 2026

142 of 145 checks passed

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@MichalStrehovsky
Revert "JIT: support SSA-aware PHI jump threading (#126812)"
108cc21
This reverts commit 578644c.
@MichalStrehovskyMichalStrehovsky
mentioned this pull request
Apr 15, 2026
 Closed

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mentioned this pull request
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9 tasks
CopilotAI
added a commit
that referenced
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Apr 16, 2026
@mangod9
Cherry-pick JIT PHI jump threading (PR#126812) with targeted fix for…
cd43a53
… global PHI use bug (#126976)
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/1507ea1a-6b49-4f3d-977a-83f9c781da83
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
CopilotAI
added a commit
that referenced
this pull request
Apr 16, 2026
@mangod9
Revert "Cherry-pick JIT PHI jump threading (PR#126812) with targeted…
5a82a7d
… fix for global PHI use bug (#126976)"
This reverts commit cd43a53.
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
this pull request
Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
3af24b7
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
this pull request
Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
d86b525
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
@AndyAyersMSAndyAyersMS
mentioned this pull request
Apr 18, 2026
 Merged

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Apr 20, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading (#127103)
9850fe0
Teach redundant branch elimination to keep jump threading through
PHI-based blocks when the PHI uses can be fully accounted for in the
block and its immediate successors. Rewrite the affected successor
SSA/VN uses, keep dominating-block threading conservative, and add
focused regression coverage for the new PHI-based cases.
Fix included here that was not in #126812: ensure that field uses of
locals get the proper VN updates.
Fixes#126976.
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
JIT: support SSA-aware PHI jump threading - #126812
Merged
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AndyAyersMS:RboSimpleSSAUpdates
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JIT: support SSA-aware PHI jump threading#126812
AndyAyersMS merged 2 commits into
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Teach redundant branch elimination to keep jump threading through PHI- based blocks when the PHI uses can be fully accounted for in the block and its immediate successors. Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative, and add focused regression coverage for the new PHI-based cases.
Fixes#126703 (not quite, yet)
@AndyAyersMS
JIT: support SSA-aware PHI jump threading
644b5f7
Teach redundant branch elimination to keep jump threading through PHI-
based blocks when the PHI uses can be fully accounted for in the block
and its immediate successors. Rewrite the affected successor SSA/VN uses,
keep dominating-block threading conservative, and add focused regression
coverage for the new PHI-based cases.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
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Pull request overview
This PR extends CoreCLR JIT redundant branch optimization (jump threading) to support PHI-based threading when PHI definitions have non-local uses, by accounting for those uses within the threaded block and its immediate successors and rewriting successor SSA/VN uses accordingly. It also adds a focused JIT regression test to cover the new PHI-based scenario.
Changes:
  • Add tracking of PHI SSA uses in the candidate block/successors and rewrite successor SSA/VN uses when threading bypasses the PHI block.
  • Refine jump-thread eligibility checking to return a richer classification (including “needs PHI use resolution”).
  • Add a new JIT test case (JumpThreadPhi) to validate the new behavior.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/jit/redundantbranchopts.cppImplements PHI-use discovery and successor SSA/VN rewriting; updates jump-thread check flow.
src/coreclr/jit/compiler.hIntroduces JumpThreadCheckResult and declares new helper methods for PHI-use analysis/rewriting.
src/coreclr/jit/compmemkind.hAdds a dedicated allocator kind for redundant-branch/jump-threading data.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csAdds regression coverage for PHI-based jump threading through a PHI-producing pattern.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csprojAdds the test project definition consistent with existing tests in the folder.
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Follow-on to #126711.
If all the uses of a global phi in a jump-threading candidate block are in the block and its successors, we can (in most cases) allow jump threading and rewrite the successor uses to the appropriate new ssa def & vn.
We avoid cases where the successors already have PHIs or would need to have new PHIs. These seem somewhat rare.
@EgorBo PTAL

fyi @dotnet/jit-contrib
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Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Thanks for filing a fix for this!
@AndyAyersMS
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Thanks for filing a fix for this!
There are a couple of follow-ons coming that should let us actually fix #126703, but I think this is a good improvement on its own.
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Diffs
Linux x64 is probably most representative, other os/arch seem to be missing some collections.
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/ba-g dead-letter mac catalyst
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Revert "JIT: support SSA-aware PHI jump threading (#126812)"
108cc21
This reverts commit 578644c.
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@mangod9
Cherry-pick JIT PHI jump threading (PR#126812) with targeted fix for…
cd43a53
… global PHI use bug (#126976)
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/1507ea1a-6b49-4f3d-977a-83f9c781da83
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
CopilotAI
added a commit
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Apr 16, 2026
@mangod9
Revert "Cherry-pick JIT PHI jump threading (PR#126812) with targeted…
5a82a7d
… fix for global PHI use bug (#126976)"
This reverts commit cd43a53.
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
this pull request
Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
3af24b7
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
this pull request
Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
d86b525
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
@AndyAyersMSAndyAyersMS
mentioned this pull request
Apr 18, 2026
 Merged

AndyAyersMS added a commit
that referenced
this pull request
Apr 20, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading (#127103)
9850fe0
Teach redundant branch elimination to keep jump threading through
PHI-based blocks when the PHI uses can be fully accounted for in the
block and its immediate successors. Rewrite the affected successor
SSA/VN uses, keep dominating-block threading conservative, and add
focused regression coverage for the new PHI-based cases.
Fix included here that was not in #126812: ensure that field uses of
locals get the proper VN updates.
Fixes#126976.
@svicksvick
mentioned this pull request
Apr 21, 2026

Closed

@LoopedBard3LoopedBard3
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Apr 23, 2026

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JIT: missing opportunity for RBO


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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
JIT: support SSA-aware PHI jump threading - #126812
Merged
AndyAyersMS merged 2 commits into
dotnet:mainfrom 
AndyAyersMS:RboSimpleSSAUpdates
Apr 13, 2026
Merged
JIT: support SSA-aware PHI jump threading#126812
AndyAyersMS merged 2 commits into
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Apr 12, 2026•

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Teach redundant branch elimination to keep jump threading through PHI- based blocks when the PHI uses can be fully accounted for in the block and its immediate successors. Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative, and add focused regression coverage for the new PHI-based cases.
Fixes#126703 (not quite, yet)
@AndyAyersMS
JIT: support SSA-aware PHI jump threading
644b5f7
Teach redundant branch elimination to keep jump threading through PHI-
based blocks when the PHI uses can be fully accounted for in the block
and its immediate successors. Rewrite the affected successor SSA/VN uses,
keep dominating-block threading conservative, and add focused regression
coverage for the new PHI-based cases.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
April 12, 2026 20:29
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CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
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Pull request overview
This PR extends CoreCLR JIT redundant branch optimization (jump threading) to support PHI-based threading when PHI definitions have non-local uses, by accounting for those uses within the threaded block and its immediate successors and rewriting successor SSA/VN uses accordingly. It also adds a focused JIT regression test to cover the new PHI-based scenario.
Changes:
  • Add tracking of PHI SSA uses in the candidate block/successors and rewrite successor SSA/VN uses when threading bypasses the PHI block.
  • Refine jump-thread eligibility checking to return a richer classification (including “needs PHI use resolution”).
  • Add a new JIT test case (JumpThreadPhi) to validate the new behavior.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/jit/redundantbranchopts.cppImplements PHI-use discovery and successor SSA/VN rewriting; updates jump-thread check flow.
src/coreclr/jit/compiler.hIntroduces JumpThreadCheckResult and declares new helper methods for PHI-use analysis/rewriting.
src/coreclr/jit/compmemkind.hAdds a dedicated allocator kind for redundant-branch/jump-threading data.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csAdds regression coverage for PHI-based jump threading through a PHI-producing pattern.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csprojAdds the test project definition consistent with existing tests in the folder.
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Outdated

Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
@AndyAyersMS
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Follow-on to #126711.
If all the uses of a global phi in a jump-threading candidate block are in the block and its successors, we can (in most cases) allow jump threading and rewrite the successor uses to the appropriate new ssa def & vn.
We avoid cases where the successors already have PHIs or would need to have new PHIs. These seem somewhat rare.
@EgorBo PTAL

fyi @dotnet/jit-contrib
@build-analysisbuild-analysisBot
mentioned this pull request
Apr 12, 2026

Closed

EgorBo
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Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Thanks for filing a fix for this!
@AndyAyersMS
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Thanks for filing a fix for this!
There are a couple of follow-ons coming that should let us actually fix #126703, but I think this is a good improvement on its own.
@AndyAyersMS
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commented
Apr 13, 2026

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Diffs
Linux x64 is probably most representative, other os/arch seem to be missing some collections.
@AndyAyersMS
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enabled auto-merge (squash)
April 13, 2026 22:50
@AndyAyersMS
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/ba-g dead-letter mac catalyst
@AndyAyersMS
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merged commit 578644c
into
dotnet:mainApr 13, 2026

142 of 145 checks passed

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@MichalStrehovsky
Revert "JIT: support SSA-aware PHI jump threading (#126812)"
108cc21
This reverts commit 578644c.
@MichalStrehovskyMichalStrehovsky
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Apr 15, 2026
 Closed

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mentioned this pull request
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9 tasks
CopilotAI
added a commit
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Apr 16, 2026
@mangod9
Cherry-pick JIT PHI jump threading (PR#126812) with targeted fix for…
cd43a53
… global PHI use bug (#126976)
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/1507ea1a-6b49-4f3d-977a-83f9c781da83
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
CopilotAI
added a commit
that referenced
this pull request
Apr 16, 2026
@mangod9
Revert "Cherry-pick JIT PHI jump threading (PR#126812) with targeted…
5a82a7d
… fix for global PHI use bug (#126976)"
This reverts commit cd43a53.
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
this pull request
Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
3af24b7
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
this pull request
Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
d86b525
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
@AndyAyersMSAndyAyersMS
mentioned this pull request
Apr 18, 2026
 Merged

AndyAyersMS added a commit
that referenced
this pull request
Apr 20, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading (#127103)
9850fe0
Teach redundant branch elimination to keep jump threading through
PHI-based blocks when the PHI uses can be fully accounted for in the
block and its immediate successors. Rewrite the affected successor
SSA/VN uses, keep dominating-block threading conservative, and add
focused regression coverage for the new PHI-based cases.
Fix included here that was not in #126812: ensure that field uses of
locals get the proper VN updates.
Fixes#126976.
@svicksvick
mentioned this pull request
Apr 21, 2026

Closed

@LoopedBard3LoopedBard3
mentioned this pull request
Apr 23, 2026

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JIT: missing opportunity for RBO


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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
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} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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JIT: support SSA-aware PHI jump threading - #126812
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AndyAyersMS:RboSimpleSSAUpdates
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JIT: support SSA-aware PHI jump threading#126812
AndyAyersMS merged 2 commits into
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Teach redundant branch elimination to keep jump threading through PHI- based blocks when the PHI uses can be fully accounted for in the block and its immediate successors. Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative, and add focused regression coverage for the new PHI-based cases.
Fixes#126703 (not quite, yet)
@AndyAyersMS
JIT: support SSA-aware PHI jump threading
644b5f7
Teach redundant branch elimination to keep jump threading through PHI-
based blocks when the PHI uses can be fully accounted for in the block
and its immediate successors. Rewrite the affected successor SSA/VN uses,
keep dominating-block threading conservative, and add focused regression
coverage for the new PHI-based cases.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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review requested due to automatic review settings
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Pull request overview
This PR extends CoreCLR JIT redundant branch optimization (jump threading) to support PHI-based threading when PHI definitions have non-local uses, by accounting for those uses within the threaded block and its immediate successors and rewriting successor SSA/VN uses accordingly. It also adds a focused JIT regression test to cover the new PHI-based scenario.
Changes:
  • Add tracking of PHI SSA uses in the candidate block/successors and rewrite successor SSA/VN uses when threading bypasses the PHI block.
  • Refine jump-thread eligibility checking to return a richer classification (including “needs PHI use resolution”).
  • Add a new JIT test case (JumpThreadPhi) to validate the new behavior.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
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FileDescription
src/coreclr/jit/redundantbranchopts.cppImplements PHI-use discovery and successor SSA/VN rewriting; updates jump-thread check flow.
src/coreclr/jit/compiler.hIntroduces JumpThreadCheckResult and declares new helper methods for PHI-use analysis/rewriting.
src/coreclr/jit/compmemkind.hAdds a dedicated allocator kind for redundant-branch/jump-threading data.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csAdds regression coverage for PHI-based jump threading through a PHI-producing pattern.
src/tests/JIT/opt/RedundantBranch/JumpThreadPhi.csprojAdds the test project definition consistent with existing tests in the folder.
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
Comment threadsrc/coreclr/jit/redundantbranchopts.cpp
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Follow-on to #126711.
If all the uses of a global phi in a jump-threading candidate block are in the block and its successors, we can (in most cases) allow jump threading and rewrite the successor uses to the appropriate new ssa def & vn.
We avoid cases where the successors already have PHIs or would need to have new PHIs. These seem somewhat rare.
@EgorBo PTAL

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Thanks for filing a fix for this!
@AndyAyersMS
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Thanks for filing a fix for this!
There are a couple of follow-ons coming that should let us actually fix #126703, but I think this is a good improvement on its own.
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Diffs
Linux x64 is probably most representative, other os/arch seem to be missing some collections.
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/ba-g dead-letter mac catalyst
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Revert "JIT: support SSA-aware PHI jump threading (#126812)"
108cc21
This reverts commit 578644c.
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Cherry-pick JIT PHI jump threading (PR#126812) with targeted fix for…
cd43a53
… global PHI use bug (#126976)
Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/1507ea1a-6b49-4f3d-977a-83f9c781da83
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
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Revert "Cherry-pick JIT PHI jump threading (PR#126812) with targeted…
5a82a7d
… fix for global PHI use bug (#126976)"
This reverts commit cd43a53.
Co-authored-by: mangod9 <61718172+mangod9@users.noreply.github.com>
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@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
3af24b7
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
AndyAyersMS added a commit
to AndyAyersMS/runtime
that referenced
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Apr 18, 2026
@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading
d86b525
Teach redundant branch elimination to keep jump threading through PHI-based blocks
when the PHI uses can be fully accounted for in the block and its immediate successors.
Rewrite the affected successor SSA/VN uses, keep dominating-block threading conservative,
and add focused regression coverage for the new PHI-based cases.
Fix included here that was not in dotnet#126812: ensure that field uses of locals get
the proper VN updates.
Fixesdotnet#126976.
@AndyAyersMSAndyAyersMS
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@AndyAyersMS
JIT: Renable SSA-aware PHI jump threading (#127103)
9850fe0
Teach redundant branch elimination to keep jump threading through
PHI-based blocks when the PHI uses can be fully accounted for in the
block and its immediate successors. Rewrite the affected successor
SSA/VN uses, keep dominating-block threading conservative, and add
focused regression coverage for the new PHI-based cases.
Fix included here that was not in #126812: ensure that field uses of
locals get the proper VN updates.
Fixes#126976.
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