JIT: fix loop cloning condition for decreasing loops with array-length limit - #129187

Merged
AndyAyersMS merged 1 commit into
dotnet:mainfrom
AndyAyersMS:fix-129176-decreasing-loopclone
Jun 9, 2026
Merged

JIT: fix loop cloning condition for decreasing loops with array-length limit#129187
AndyAyersMS merged 1 commit into
dotnet:mainfrom
AndyAyersMS:fix-129176-decreasing-loopclone

Conversation

@AndyAyersMS

@AndyAyersMSAndyAyersMS commented Jun 9, 2026

Copy link
Copy Markdown
Member

optDeriveLoopCloningConditions was unconditionally overwriting ident with the limit array's length in the HasArrayLengthLimit branch, leaving decreasing loops with the wrong per-access condition (limit <relop> accessArr.Length instead of init <relop> accessArr.Length). Gate the overwrite on isIncreasingLoop to match the parallel HasConstLimit and HasInvariantLocalLimit branches.

Fixes#129176.

@AndyAyersMS
JIT: fix loop cloning condition for decreasing loops with array-lengt…
b6c57bf
…h limit
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident` with
the limit array's length in the `HasArrayLengthLimit` branch, leaving
decreasing loops with the wrong per-access condition (`limit <relop>
accessArr.Length` instead of `init <relop> accessArr.Length`). Gate the
overwrite on `isIncreasingLoop` to match the parallel `HasConstLimit` and
`HasInvariantLocalLimit` branches.
Fixesdotnet#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI review requested due to automatic review settings June 9, 2026 18:37
@github-actionsgithub-actionsBot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Jun 9, 2026
@AndyAyersMS

AndyAyersMS commented Jun 9, 2026

Copy link
Copy Markdown
MemberAuthor

@jakobbotsch PTAL
fyi @dotnet/jit-contrib

Bug has been in the code since .NET 7, so may not be a strong case for a backport.

CopilotAI reviewed Jun 9, 2026
View reviewed changes

CopilotAI left a comment

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Pull request overview

This PR fixes loop-cloning condition derivation in optDeriveLoopCloningConditions for decreasing loops when the loop limit is an array length, ensuring the per-access bounds condition is derived from the loop init (upper end of the decreasing IV range) rather than incorrectly overwriting it with the limit array’s .Length. It also adds a JIT regression test covering the unsafe fast-clone scenario.

Changes:

  • Fix: In HasArrayLengthLimit, only overwrite ident with the limit array length for increasing loops (leave decreasing-loop ident as the init-derived identifier).
  • Tests: Add a new JitBlue regression test that ensures decreasing loops with mismatched limit/indexed arrays still throw IndexOutOfRangeException when init is out of bounds.
  • Build/test wiring: Include the new test source file in Regression_ro_2.csproj.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

FileDescription
src/coreclr/jit/loopcloning.cppGates ident overwrite in HasArrayLengthLimit to increasing loops so decreasing loops keep init-based per-access conditions.
src/tests/JIT/Regression/Regression_ro_2.csprojAdds compile include for the new JIT regression test.
src/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.csNew regression test exercising decreasing-loop cloning correctness when limit and indexed arrays differ.

Comment threadsrc/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.cs
@AndyAyersMS

AndyAyersMS commented Jun 9, 2026

Copy link
Copy Markdown
MemberAuthor

interestingly there is one method with a diff

@AndyAyersMSAndyAyersMS mentioned this pull request Jun 9, 2026
Open
@AndyAyersMS
AndyAyersMS merged commit 65937ca into dotnet:mainJun 9, 2026
144 of 147 checks passed
This was referenced Jun 10, 2026
Closed
Merged
@dotnet-milestone-botdotnet-milestone-botBot added this to the 11.0-preview6 milestone Jun 17, 2026
@maestro-local-devmaestro-local-devBot mentioned this pull request Jun 23, 2026
Open
eiriktsarpalis pushed a commit that referenced this pull request Jul 15, 2026
@AndyAyersMS@eiriktsarpalis
JIT: fix loop cloning condition for decreasing loops with array-lengt…
e686e1f
…h limit (#129187)
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident`
with the limit array's length in the `HasArrayLengthLimit` branch,
leaving decreasing loops with the wrong per-access condition (`limit
<relop> accessArr.Length` instead of `init <relop> accessArr.Length`).
Gate the overwrite on `isIncreasingLoop` to match the parallel
`HasConstLimit` and `HasInvariantLocalLimit` branches.
Fixes#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot locked and limited conversation to collaborators Jul 18, 2026
Sign up for freeto subscribe to this conversation on GitHub. Already have an account? Sign in.

Reviewers

Copilot code reviewCopilot
Copilot review effort
Applies to this pull request for everyone.Learn more about Copilot code review.
Copilot left review comments
@jakobbotschjakobbotschjakobbotsch approved these changes

Assignees

No one assigned

Labels

area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI

Projects

None yet

Milestone

11.0-preview6

Development

Successfully merging this pull request may close these issues.

JIT: loop cloning generates unsafe fast clone for decreasing loops when limit and indexed arrays differ

3 participants

@AndyAyersMS@jakobbotsch
, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

Skip to content
JIT: fix loop cloning condition for decreasing loops with array-length limit - #129187
Merged
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Jun 9, 2026
Merged
JIT: fix loop cloning condition for decreasing loops with array-length limit#129187
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Conversation
@AndyAyersMS
@AndyAyersMSAndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

Member
optDeriveLoopCloningConditions was unconditionally overwriting ident with the limit array's length in the HasArrayLengthLimit branch, leaving decreasing loops with the wrong per-access condition (limit <relop> accessArr.Length instead of init <relop> accessArr.Length). Gate the overwrite on isIncreasingLoop to match the parallel HasConstLimit and HasInvariantLocalLimit branches.
Fixes#129176.
@AndyAyersMS
JIT: fix loop cloning condition for decreasing loops with array-lengt…
b6c57bf
…h limit
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident` with
the limit array's length in the `HasArrayLengthLimit` branch, leaving
decreasing loops with the wrong per-access condition (`limit <relop>
accessArr.Length` instead of `init <relop> accessArr.Length`). Gate the
overwrite on `isIncreasingLoop` to match the parallel `HasConstLimit` and
`HasInvariantLocalLimit` branches.
Fixesdotnet#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
June 9, 2026 18:37
@github-actionsgithub-actionsBot
added
the 
area-CodeGen-coreclr
CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
label
Jun 9, 2026
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
@jakobbotsch PTAL

fyi @dotnet/jit-contrib
Bug has been in the code since .NET 7, so may not be a strong case for a backport.
CopilotAI
reviewed
Jun 9, 2026
View reviewed changes
CopilotAI
left a comment


Copy link


Copy Markdown

Contributor
Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Pull request overview
This PR fixes loop-cloning condition derivation in optDeriveLoopCloningConditions for decreasing loops when the loop limit is an array length, ensuring the per-access bounds condition is derived from the loop init (upper end of the decreasing IV range) rather than incorrectly overwriting it with the limit array’s .Length. It also adds a JIT regression test covering the unsafe fast-clone scenario.
Changes:
  • Fix: In HasArrayLengthLimit, only overwrite ident with the limit array length for increasing loops (leave decreasing-loop ident as the init-derived identifier).
  • Tests: Add a new JitBlue regression test that ensures decreasing loops with mismatched limit/indexed arrays still throw IndexOutOfRangeException when init is out of bounds.
  • Build/test wiring: Include the new test source file in Regression_ro_2.csproj.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/jit/loopcloning.cppGates ident overwrite in HasArrayLengthLimit to increasing loops so decreasing loops keep init-based per-access conditions.
src/tests/JIT/Regression/Regression_ro_2.csprojAdds compile include for the new JIT regression test.
src/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.csNew regression test exercising decreasing-loop cloning correctness when limit and indexed arrays differ.
Comment threadsrc/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.cs
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
interestingly there is one method with a diff
@AndyAyersMSAndyAyersMS
mentioned this pull request
Jun 9, 2026

Open

@AndyAyersMS
AndyAyersMS
merged commit 65937ca
into
dotnet:mainJun 9, 2026

144 of 147 checks passed


This was referenced Jun 10, 2026
 Closed

 Merged

@dotnet-milestone-botdotnet-milestone-botBot
added this to the 11.0-preview6 milestone
Jun 17, 2026
@maestro-local-devmaestro-local-devBot
mentioned this pull request
Jun 23, 2026
 Open

eiriktsarpalis pushed a commit
that referenced
this pull request
Jul 15, 2026
@AndyAyersMS@eiriktsarpalis
JIT: fix loop cloning condition for decreasing loops with array-lengt…
e686e1f
…h limit (#129187)
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident`
with the limit array's length in the `HasArrayLengthLimit` branch,
leaving decreasing loops with the wrong per-access condition (`limit
<relop> accessArr.Length` instead of `init <relop> accessArr.Length`).
Gate the overwrite on `isIncreasingLoop` to match the parallel
`HasConstLimit` and `HasInvariantLocalLimit` branches.
Fixes#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot
locked and limited conversation to collaborators
Jul 18, 2026
Sign up for freeto subscribe to this conversation on GitHub.
Already have an account?
Sign in.


Reviewers

Copilot code reviewCopilot
Copilot review effort
Applies to this pull request for everyone.Learn more about Copilot code review.
Copilot left review comments
@jakobbotschjakobbotschjakobbotsch approved these changes

Assignees


No one assigned


Labels

area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI

Projects


None yet


Milestone

11.0-preview6

Development

Successfully merging this pull request may close these issues.

JIT: loop cloning generates unsafe fast clone for decreasing loops when limit and indexed arrays differ


3 participants

@AndyAyersMS@jakobbotsch

, '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");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
JIT: fix loop cloning condition for decreasing loops with array-length limit - #129187
Merged
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Jun 9, 2026
Merged
JIT: fix loop cloning condition for decreasing loops with array-length limit#129187
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Conversation
@AndyAyersMS
@AndyAyersMSAndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

Member
optDeriveLoopCloningConditions was unconditionally overwriting ident with the limit array's length in the HasArrayLengthLimit branch, leaving decreasing loops with the wrong per-access condition (limit <relop> accessArr.Length instead of init <relop> accessArr.Length). Gate the overwrite on isIncreasingLoop to match the parallel HasConstLimit and HasInvariantLocalLimit branches.
Fixes#129176.
@AndyAyersMS
JIT: fix loop cloning condition for decreasing loops with array-lengt…
b6c57bf
…h limit
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident` with
the limit array's length in the `HasArrayLengthLimit` branch, leaving
decreasing loops with the wrong per-access condition (`limit <relop>
accessArr.Length` instead of `init <relop> accessArr.Length`). Gate the
overwrite on `isIncreasingLoop` to match the parallel `HasConstLimit` and
`HasInvariantLocalLimit` branches.
Fixesdotnet#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
June 9, 2026 18:37
@github-actionsgithub-actionsBot
added
the 
area-CodeGen-coreclr
CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
label
Jun 9, 2026
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
@jakobbotsch PTAL

fyi @dotnet/jit-contrib
Bug has been in the code since .NET 7, so may not be a strong case for a backport.
CopilotAI
reviewed
Jun 9, 2026
View reviewed changes
CopilotAI
left a comment


Copy link


Copy Markdown

Contributor
Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Pull request overview
This PR fixes loop-cloning condition derivation in optDeriveLoopCloningConditions for decreasing loops when the loop limit is an array length, ensuring the per-access bounds condition is derived from the loop init (upper end of the decreasing IV range) rather than incorrectly overwriting it with the limit array’s .Length. It also adds a JIT regression test covering the unsafe fast-clone scenario.
Changes:
  • Fix: In HasArrayLengthLimit, only overwrite ident with the limit array length for increasing loops (leave decreasing-loop ident as the init-derived identifier).
  • Tests: Add a new JitBlue regression test that ensures decreasing loops with mismatched limit/indexed arrays still throw IndexOutOfRangeException when init is out of bounds.
  • Build/test wiring: Include the new test source file in Regression_ro_2.csproj.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/jit/loopcloning.cppGates ident overwrite in HasArrayLengthLimit to increasing loops so decreasing loops keep init-based per-access conditions.
src/tests/JIT/Regression/Regression_ro_2.csprojAdds compile include for the new JIT regression test.
src/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.csNew regression test exercising decreasing-loop cloning correctness when limit and indexed arrays differ.
Comment threadsrc/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.cs
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
interestingly there is one method with a diff
@AndyAyersMSAndyAyersMS
mentioned this pull request
Jun 9, 2026

Open

@AndyAyersMS
AndyAyersMS
merged commit 65937ca
into
dotnet:mainJun 9, 2026

144 of 147 checks passed


This was referenced Jun 10, 2026
 Closed

 Merged

@dotnet-milestone-botdotnet-milestone-botBot
added this to the 11.0-preview6 milestone
Jun 17, 2026
@maestro-local-devmaestro-local-devBot
mentioned this pull request
Jun 23, 2026
 Open

eiriktsarpalis pushed a commit
that referenced
this pull request
Jul 15, 2026
@AndyAyersMS@eiriktsarpalis
JIT: fix loop cloning condition for decreasing loops with array-lengt…
e686e1f
…h limit (#129187)
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident`
with the limit array's length in the `HasArrayLengthLimit` branch,
leaving decreasing loops with the wrong per-access condition (`limit
<relop> accessArr.Length` instead of `init <relop> accessArr.Length`).
Gate the overwrite on `isIncreasingLoop` to match the parallel
`HasConstLimit` and `HasInvariantLocalLimit` branches.
Fixes#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot
locked and limited conversation to collaborators
Jul 18, 2026
Sign up for freeto subscribe to this conversation on GitHub.
Already have an account?
Sign in.


Reviewers

Copilot code reviewCopilot
Copilot review effort
Applies to this pull request for everyone.Learn more about Copilot code review.
Copilot left review comments
@jakobbotschjakobbotschjakobbotsch approved these changes

Assignees


No one assigned


Labels

area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI

Projects


None yet


Milestone

11.0-preview6

Development

Successfully merging this pull request may close these issues.

JIT: loop cloning generates unsafe fast clone for decreasing loops when limit and indexed arrays differ


3 participants

@AndyAyersMS@jakobbotsch

, '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('^' + ".*" + '

Skip to content
JIT: fix loop cloning condition for decreasing loops with array-length limit - #129187
Merged
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Jun 9, 2026
Merged
JIT: fix loop cloning condition for decreasing loops with array-length limit#129187
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Conversation
@AndyAyersMS
@AndyAyersMSAndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

Member
optDeriveLoopCloningConditions was unconditionally overwriting ident with the limit array's length in the HasArrayLengthLimit branch, leaving decreasing loops with the wrong per-access condition (limit <relop> accessArr.Length instead of init <relop> accessArr.Length). Gate the overwrite on isIncreasingLoop to match the parallel HasConstLimit and HasInvariantLocalLimit branches.
Fixes#129176.
@AndyAyersMS
JIT: fix loop cloning condition for decreasing loops with array-lengt…
b6c57bf
…h limit
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident` with
the limit array's length in the `HasArrayLengthLimit` branch, leaving
decreasing loops with the wrong per-access condition (`limit <relop>
accessArr.Length` instead of `init <relop> accessArr.Length`). Gate the
overwrite on `isIncreasingLoop` to match the parallel `HasConstLimit` and
`HasInvariantLocalLimit` branches.
Fixesdotnet#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
June 9, 2026 18:37
@github-actionsgithub-actionsBot
added
the 
area-CodeGen-coreclr
CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
label
Jun 9, 2026
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
@jakobbotsch PTAL

fyi @dotnet/jit-contrib
Bug has been in the code since .NET 7, so may not be a strong case for a backport.
CopilotAI
reviewed
Jun 9, 2026
View reviewed changes
CopilotAI
left a comment


Copy link


Copy Markdown

Contributor
Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Pull request overview
This PR fixes loop-cloning condition derivation in optDeriveLoopCloningConditions for decreasing loops when the loop limit is an array length, ensuring the per-access bounds condition is derived from the loop init (upper end of the decreasing IV range) rather than incorrectly overwriting it with the limit array’s .Length. It also adds a JIT regression test covering the unsafe fast-clone scenario.
Changes:
  • Fix: In HasArrayLengthLimit, only overwrite ident with the limit array length for increasing loops (leave decreasing-loop ident as the init-derived identifier).
  • Tests: Add a new JitBlue regression test that ensures decreasing loops with mismatched limit/indexed arrays still throw IndexOutOfRangeException when init is out of bounds.
  • Build/test wiring: Include the new test source file in Regression_ro_2.csproj.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/jit/loopcloning.cppGates ident overwrite in HasArrayLengthLimit to increasing loops so decreasing loops keep init-based per-access conditions.
src/tests/JIT/Regression/Regression_ro_2.csprojAdds compile include for the new JIT regression test.
src/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.csNew regression test exercising decreasing-loop cloning correctness when limit and indexed arrays differ.
Comment threadsrc/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.cs
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
interestingly there is one method with a diff
@AndyAyersMSAndyAyersMS
mentioned this pull request
Jun 9, 2026

Open

@AndyAyersMS
AndyAyersMS
merged commit 65937ca
into
dotnet:mainJun 9, 2026

144 of 147 checks passed


This was referenced Jun 10, 2026
 Closed

 Merged

@dotnet-milestone-botdotnet-milestone-botBot
added this to the 11.0-preview6 milestone
Jun 17, 2026
@maestro-local-devmaestro-local-devBot
mentioned this pull request
Jun 23, 2026
 Open

eiriktsarpalis pushed a commit
that referenced
this pull request
Jul 15, 2026
@AndyAyersMS@eiriktsarpalis
JIT: fix loop cloning condition for decreasing loops with array-lengt…
e686e1f
…h limit (#129187)
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident`
with the limit array's length in the `HasArrayLengthLimit` branch,
leaving decreasing loops with the wrong per-access condition (`limit
<relop> accessArr.Length` instead of `init <relop> accessArr.Length`).
Gate the overwrite on `isIncreasingLoop` to match the parallel
`HasConstLimit` and `HasInvariantLocalLimit` branches.
Fixes#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot
locked and limited conversation to collaborators
Jul 18, 2026
Sign up for freeto subscribe to this conversation on GitHub.
Already have an account?
Sign in.


Reviewers

Copilot code reviewCopilot
Copilot review effort
Applies to this pull request for everyone.Learn more about Copilot code review.
Copilot left review comments
@jakobbotschjakobbotschjakobbotsch approved these changes

Assignees


No one assigned


Labels

area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI

Projects


None yet


Milestone

11.0-preview6

Development

Successfully merging this pull request may close these issues.

JIT: loop cloning generates unsafe fast clone for decreasing loops when limit and indexed arrays differ


3 participants

@AndyAyersMS@jakobbotsch

, '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: fix loop cloning condition for decreasing loops with array-length limit - #129187
Merged
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Jun 9, 2026
Merged
JIT: fix loop cloning condition for decreasing loops with array-length limit#129187
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Conversation
@AndyAyersMS
@AndyAyersMSAndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

Member
optDeriveLoopCloningConditions was unconditionally overwriting ident with the limit array's length in the HasArrayLengthLimit branch, leaving decreasing loops with the wrong per-access condition (limit <relop> accessArr.Length instead of init <relop> accessArr.Length). Gate the overwrite on isIncreasingLoop to match the parallel HasConstLimit and HasInvariantLocalLimit branches.
Fixes#129176.
@AndyAyersMS
JIT: fix loop cloning condition for decreasing loops with array-lengt…
b6c57bf
…h limit
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident` with
the limit array's length in the `HasArrayLengthLimit` branch, leaving
decreasing loops with the wrong per-access condition (`limit <relop>
accessArr.Length` instead of `init <relop> accessArr.Length`). Gate the
overwrite on `isIncreasingLoop` to match the parallel `HasConstLimit` and
`HasInvariantLocalLimit` branches.
Fixesdotnet#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
June 9, 2026 18:37
@github-actionsgithub-actionsBot
added
the 
area-CodeGen-coreclr
CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
label
Jun 9, 2026
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
@jakobbotsch PTAL

fyi @dotnet/jit-contrib
Bug has been in the code since .NET 7, so may not be a strong case for a backport.
CopilotAI
reviewed
Jun 9, 2026
View reviewed changes
CopilotAI
left a comment


Copy link


Copy Markdown

Contributor
Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Pull request overview
This PR fixes loop-cloning condition derivation in optDeriveLoopCloningConditions for decreasing loops when the loop limit is an array length, ensuring the per-access bounds condition is derived from the loop init (upper end of the decreasing IV range) rather than incorrectly overwriting it with the limit array’s .Length. It also adds a JIT regression test covering the unsafe fast-clone scenario.
Changes:
  • Fix: In HasArrayLengthLimit, only overwrite ident with the limit array length for increasing loops (leave decreasing-loop ident as the init-derived identifier).
  • Tests: Add a new JitBlue regression test that ensures decreasing loops with mismatched limit/indexed arrays still throw IndexOutOfRangeException when init is out of bounds.
  • Build/test wiring: Include the new test source file in Regression_ro_2.csproj.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/jit/loopcloning.cppGates ident overwrite in HasArrayLengthLimit to increasing loops so decreasing loops keep init-based per-access conditions.
src/tests/JIT/Regression/Regression_ro_2.csprojAdds compile include for the new JIT regression test.
src/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.csNew regression test exercising decreasing-loop cloning correctness when limit and indexed arrays differ.
Comment threadsrc/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.cs
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
interestingly there is one method with a diff
@AndyAyersMSAndyAyersMS
mentioned this pull request
Jun 9, 2026

Open

@AndyAyersMS
AndyAyersMS
merged commit 65937ca
into
dotnet:mainJun 9, 2026

144 of 147 checks passed


This was referenced Jun 10, 2026
 Closed

 Merged

@dotnet-milestone-botdotnet-milestone-botBot
added this to the 11.0-preview6 milestone
Jun 17, 2026
@maestro-local-devmaestro-local-devBot
mentioned this pull request
Jun 23, 2026
 Open

eiriktsarpalis pushed a commit
that referenced
this pull request
Jul 15, 2026
@AndyAyersMS@eiriktsarpalis
JIT: fix loop cloning condition for decreasing loops with array-lengt…
e686e1f
…h limit (#129187)
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident`
with the limit array's length in the `HasArrayLengthLimit` branch,
leaving decreasing loops with the wrong per-access condition (`limit
<relop> accessArr.Length` instead of `init <relop> accessArr.Length`).
Gate the overwrite on `isIncreasingLoop` to match the parallel
`HasConstLimit` and `HasInvariantLocalLimit` branches.
Fixes#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot
locked and limited conversation to collaborators
Jul 18, 2026
Sign up for freeto subscribe to this conversation on GitHub.
Already have an account?
Sign in.


Reviewers

Copilot code reviewCopilot
Copilot review effort
Applies to this pull request for everyone.Learn more about Copilot code review.
Copilot left review comments
@jakobbotschjakobbotschjakobbotsch approved these changes

Assignees


No one assigned


Labels

area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI

Projects


None yet


Milestone

11.0-preview6

Development

Successfully merging this pull request may close these issues.

JIT: loop cloning generates unsafe fast clone for decreasing loops when limit and indexed arrays differ


3 participants

@AndyAyersMS@jakobbotsch

, '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: fix loop cloning condition for decreasing loops with array-length limit - #129187
Merged
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Jun 9, 2026
Merged
JIT: fix loop cloning condition for decreasing loops with array-length limit#129187
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Conversation
@AndyAyersMS
@AndyAyersMSAndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

Member
optDeriveLoopCloningConditions was unconditionally overwriting ident with the limit array's length in the HasArrayLengthLimit branch, leaving decreasing loops with the wrong per-access condition (limit <relop> accessArr.Length instead of init <relop> accessArr.Length). Gate the overwrite on isIncreasingLoop to match the parallel HasConstLimit and HasInvariantLocalLimit branches.
Fixes#129176.
@AndyAyersMS
JIT: fix loop cloning condition for decreasing loops with array-lengt…
b6c57bf
…h limit
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident` with
the limit array's length in the `HasArrayLengthLimit` branch, leaving
decreasing loops with the wrong per-access condition (`limit <relop>
accessArr.Length` instead of `init <relop> accessArr.Length`). Gate the
overwrite on `isIncreasingLoop` to match the parallel `HasConstLimit` and
`HasInvariantLocalLimit` branches.
Fixesdotnet#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
June 9, 2026 18:37
@github-actionsgithub-actionsBot
added
the 
area-CodeGen-coreclr
CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
label
Jun 9, 2026
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
@jakobbotsch PTAL

fyi @dotnet/jit-contrib
Bug has been in the code since .NET 7, so may not be a strong case for a backport.
CopilotAI
reviewed
Jun 9, 2026
View reviewed changes
CopilotAI
left a comment


Copy link


Copy Markdown

Contributor
Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Pull request overview
This PR fixes loop-cloning condition derivation in optDeriveLoopCloningConditions for decreasing loops when the loop limit is an array length, ensuring the per-access bounds condition is derived from the loop init (upper end of the decreasing IV range) rather than incorrectly overwriting it with the limit array’s .Length. It also adds a JIT regression test covering the unsafe fast-clone scenario.
Changes:
  • Fix: In HasArrayLengthLimit, only overwrite ident with the limit array length for increasing loops (leave decreasing-loop ident as the init-derived identifier).
  • Tests: Add a new JitBlue regression test that ensures decreasing loops with mismatched limit/indexed arrays still throw IndexOutOfRangeException when init is out of bounds.
  • Build/test wiring: Include the new test source file in Regression_ro_2.csproj.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/jit/loopcloning.cppGates ident overwrite in HasArrayLengthLimit to increasing loops so decreasing loops keep init-based per-access conditions.
src/tests/JIT/Regression/Regression_ro_2.csprojAdds compile include for the new JIT regression test.
src/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.csNew regression test exercising decreasing-loop cloning correctness when limit and indexed arrays differ.
Comment threadsrc/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.cs
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
interestingly there is one method with a diff
@AndyAyersMSAndyAyersMS
mentioned this pull request
Jun 9, 2026

Open

@AndyAyersMS
AndyAyersMS
merged commit 65937ca
into
dotnet:mainJun 9, 2026

144 of 147 checks passed


This was referenced Jun 10, 2026
 Closed

 Merged

@dotnet-milestone-botdotnet-milestone-botBot
added this to the 11.0-preview6 milestone
Jun 17, 2026
@maestro-local-devmaestro-local-devBot
mentioned this pull request
Jun 23, 2026
 Open

eiriktsarpalis pushed a commit
that referenced
this pull request
Jul 15, 2026
@AndyAyersMS@eiriktsarpalis
JIT: fix loop cloning condition for decreasing loops with array-lengt…
e686e1f
…h limit (#129187)
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident`
with the limit array's length in the `HasArrayLengthLimit` branch,
leaving decreasing loops with the wrong per-access condition (`limit
<relop> accessArr.Length` instead of `init <relop> accessArr.Length`).
Gate the overwrite on `isIncreasingLoop` to match the parallel
`HasConstLimit` and `HasInvariantLocalLimit` branches.
Fixes#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot
locked and limited conversation to collaborators
Jul 18, 2026
Sign up for freeto subscribe to this conversation on GitHub.
Already have an account?
Sign in.


Reviewers

Copilot code reviewCopilot
Copilot review effort
Applies to this pull request for everyone.Learn more about Copilot code review.
Copilot left review comments
@jakobbotschjakobbotschjakobbotsch approved these changes

Assignees


No one assigned


Labels

area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI

Projects


None yet


Milestone

11.0-preview6

Development

Successfully merging this pull request may close these issues.

JIT: loop cloning generates unsafe fast clone for decreasing loops when limit and indexed arrays differ


3 participants

@AndyAyersMS@jakobbotsch

, '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: fix loop cloning condition for decreasing loops with array-length limit - #129187
Merged
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Jun 9, 2026
Merged
JIT: fix loop cloning condition for decreasing loops with array-length limit#129187
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Conversation
@AndyAyersMS
@AndyAyersMSAndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

Member
optDeriveLoopCloningConditions was unconditionally overwriting ident with the limit array's length in the HasArrayLengthLimit branch, leaving decreasing loops with the wrong per-access condition (limit <relop> accessArr.Length instead of init <relop> accessArr.Length). Gate the overwrite on isIncreasingLoop to match the parallel HasConstLimit and HasInvariantLocalLimit branches.
Fixes#129176.
@AndyAyersMS
JIT: fix loop cloning condition for decreasing loops with array-lengt…
b6c57bf
…h limit
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident` with
the limit array's length in the `HasArrayLengthLimit` branch, leaving
decreasing loops with the wrong per-access condition (`limit <relop>
accessArr.Length` instead of `init <relop> accessArr.Length`). Gate the
overwrite on `isIncreasingLoop` to match the parallel `HasConstLimit` and
`HasInvariantLocalLimit` branches.
Fixesdotnet#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
June 9, 2026 18:37
@github-actionsgithub-actionsBot
added
the 
area-CodeGen-coreclr
CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
label
Jun 9, 2026
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
@jakobbotsch PTAL

fyi @dotnet/jit-contrib
Bug has been in the code since .NET 7, so may not be a strong case for a backport.
CopilotAI
reviewed
Jun 9, 2026
View reviewed changes
CopilotAI
left a comment


Copy link


Copy Markdown

Contributor
Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Pull request overview
This PR fixes loop-cloning condition derivation in optDeriveLoopCloningConditions for decreasing loops when the loop limit is an array length, ensuring the per-access bounds condition is derived from the loop init (upper end of the decreasing IV range) rather than incorrectly overwriting it with the limit array’s .Length. It also adds a JIT regression test covering the unsafe fast-clone scenario.
Changes:
  • Fix: In HasArrayLengthLimit, only overwrite ident with the limit array length for increasing loops (leave decreasing-loop ident as the init-derived identifier).
  • Tests: Add a new JitBlue regression test that ensures decreasing loops with mismatched limit/indexed arrays still throw IndexOutOfRangeException when init is out of bounds.
  • Build/test wiring: Include the new test source file in Regression_ro_2.csproj.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/jit/loopcloning.cppGates ident overwrite in HasArrayLengthLimit to increasing loops so decreasing loops keep init-based per-access conditions.
src/tests/JIT/Regression/Regression_ro_2.csprojAdds compile include for the new JIT regression test.
src/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.csNew regression test exercising decreasing-loop cloning correctness when limit and indexed arrays differ.
Comment threadsrc/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.cs
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
interestingly there is one method with a diff
@AndyAyersMSAndyAyersMS
mentioned this pull request
Jun 9, 2026

Open

@AndyAyersMS
AndyAyersMS
merged commit 65937ca
into
dotnet:mainJun 9, 2026

144 of 147 checks passed


This was referenced Jun 10, 2026
 Closed

 Merged

@dotnet-milestone-botdotnet-milestone-botBot
added this to the 11.0-preview6 milestone
Jun 17, 2026
@maestro-local-devmaestro-local-devBot
mentioned this pull request
Jun 23, 2026
 Open

eiriktsarpalis pushed a commit
that referenced
this pull request
Jul 15, 2026
@AndyAyersMS@eiriktsarpalis
JIT: fix loop cloning condition for decreasing loops with array-lengt…
e686e1f
…h limit (#129187)
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident`
with the limit array's length in the `HasArrayLengthLimit` branch,
leaving decreasing loops with the wrong per-access condition (`limit
<relop> accessArr.Length` instead of `init <relop> accessArr.Length`).
Gate the overwrite on `isIncreasingLoop` to match the parallel
`HasConstLimit` and `HasInvariantLocalLimit` branches.
Fixes#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot
locked and limited conversation to collaborators
Jul 18, 2026
Sign up for freeto subscribe to this conversation on GitHub.
Already have an account?
Sign in.


Reviewers

Copilot code reviewCopilot
Copilot review effort
Applies to this pull request for everyone.Learn more about Copilot code review.
Copilot left review comments
@jakobbotschjakobbotschjakobbotsch approved these changes

Assignees


No one assigned


Labels

area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI

Projects


None yet


Milestone

11.0-preview6

Development

Successfully merging this pull request may close these issues.

JIT: loop cloning generates unsafe fast clone for decreasing loops when limit and indexed arrays differ


3 participants

@AndyAyersMS@jakobbotsch

, '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");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

Skip to content
JIT: fix loop cloning condition for decreasing loops with array-length limit - #129187
Merged
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Jun 9, 2026
Merged
JIT: fix loop cloning condition for decreasing loops with array-length limit#129187
AndyAyersMS merged 1 commit into
dotnet:mainfrom 
AndyAyersMS:fix-129176-decreasing-loopclone
Conversation
@AndyAyersMS
@AndyAyersMSAndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

Member
optDeriveLoopCloningConditions was unconditionally overwriting ident with the limit array's length in the HasArrayLengthLimit branch, leaving decreasing loops with the wrong per-access condition (limit <relop> accessArr.Length instead of init <relop> accessArr.Length). Gate the overwrite on isIncreasingLoop to match the parallel HasConstLimit and HasInvariantLocalLimit branches.
Fixes#129176.
@AndyAyersMS
JIT: fix loop cloning condition for decreasing loops with array-lengt…
b6c57bf
…h limit
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident` with
the limit array's length in the `HasArrayLengthLimit` branch, leaving
decreasing loops with the wrong per-access condition (`limit <relop>
accessArr.Length` instead of `init <relop> accessArr.Length`). Gate the
overwrite on `isIncreasingLoop` to match the parallel `HasConstLimit` and
`HasInvariantLocalLimit` branches.
Fixesdotnet#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CopilotAI
review requested due to automatic review settings
June 9, 2026 18:37
@github-actionsgithub-actionsBot
added
the 
area-CodeGen-coreclr
CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
label
Jun 9, 2026
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
@jakobbotsch PTAL

fyi @dotnet/jit-contrib
Bug has been in the code since .NET 7, so may not be a strong case for a backport.
CopilotAI
reviewed
Jun 9, 2026
View reviewed changes
CopilotAI
left a comment


Copy link


Copy Markdown

Contributor
Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Pull request overview
This PR fixes loop-cloning condition derivation in optDeriveLoopCloningConditions for decreasing loops when the loop limit is an array length, ensuring the per-access bounds condition is derived from the loop init (upper end of the decreasing IV range) rather than incorrectly overwriting it with the limit array’s .Length. It also adds a JIT regression test covering the unsafe fast-clone scenario.
Changes:
  • Fix: In HasArrayLengthLimit, only overwrite ident with the limit array length for increasing loops (leave decreasing-loop ident as the init-derived identifier).
  • Tests: Add a new JitBlue regression test that ensures decreasing loops with mismatched limit/indexed arrays still throw IndexOutOfRangeException when init is out of bounds.
  • Build/test wiring: Include the new test source file in Regression_ro_2.csproj.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.
FileDescription
src/coreclr/jit/loopcloning.cppGates ident overwrite in HasArrayLengthLimit to increasing loops so decreasing loops keep init-based per-access conditions.
src/tests/JIT/Regression/Regression_ro_2.csprojAdds compile include for the new JIT regression test.
src/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.csNew regression test exercising decreasing-loop cloning correctness when limit and indexed arrays differ.
Comment threadsrc/tests/JIT/Regression/JitBlue/Runtime_129176/Runtime_129176.cs
@AndyAyersMS
AndyAyersMS
commented
Jun 9, 2026

Copy link


Copy Markdown

MemberAuthor
interestingly there is one method with a diff
@AndyAyersMSAndyAyersMS
mentioned this pull request
Jun 9, 2026

Open

@AndyAyersMS
AndyAyersMS
merged commit 65937ca
into
dotnet:mainJun 9, 2026

144 of 147 checks passed


This was referenced Jun 10, 2026
 Closed

 Merged

@dotnet-milestone-botdotnet-milestone-botBot
added this to the 11.0-preview6 milestone
Jun 17, 2026
@maestro-local-devmaestro-local-devBot
mentioned this pull request
Jun 23, 2026
 Open

eiriktsarpalis pushed a commit
that referenced
this pull request
Jul 15, 2026
@AndyAyersMS@eiriktsarpalis
JIT: fix loop cloning condition for decreasing loops with array-lengt…
e686e1f
…h limit (#129187)
`optDeriveLoopCloningConditions` was unconditionally overwriting `ident`
with the limit array's length in the `HasArrayLengthLimit` branch,
leaving decreasing loops with the wrong per-access condition (`limit
<relop> accessArr.Length` instead of `init <relop> accessArr.Length`).
Gate the overwrite on `isIncreasingLoop` to match the parallel
`HasConstLimit` and `HasInvariantLocalLimit` branches.
Fixes#129176.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
@github-actionsgithub-actionsBot
locked and limited conversation to collaborators
Jul 18, 2026
Sign up for freeto subscribe to this conversation on GitHub.
Already have an account?
Sign in.


Reviewers

Copilot code reviewCopilot
Copilot review effort
Applies to this pull request for everyone.Learn more about Copilot code review.
Copilot left review comments
@jakobbotschjakobbotschjakobbotsch approved these changes

Assignees


No one assigned


Labels

area-CodeGen-coreclrCLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI

Projects


None yet


Milestone

11.0-preview6

Development

Successfully merging this pull request may close these issues.

JIT: loop cloning generates unsafe fast clone for decreasing loops when limit and indexed arrays differ


3 participants

@AndyAyersMS@jakobbotsch