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Track dependently-promoted fields when struct local is no longer referenced. - #37280
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erozenfeld
commented
Jun 1, 2020
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Example from #1007: Example 4: usingSystem.Runtime.InteropServices;publicclassC{[StructLayout(LayoutKind.Sequential,Size=24)]publicstructBuffer{publiculongField1;publiculongField2;publicuintField3;}publicvoidM(){varbuf=newBuffer();buf.Field1=2;}}Diffs after #36918 (optimization to remove zero inits): G_M25775_IG01:
4883EC18 sub rsp, 24
- C5F877 vzeroupper
C5D857E4 vxorps xmm4, xmm4
C5F97F2424 vmovdqa xmmword ptr [rsp], xmm4
33C0 xor rax, rax
4889442410 mov qword ptr [rsp+10H], rax
;; bbWeight=1 PerfScore 3.83
G_M25775_IG02:
- 33C0 xor eax, eax- C5F857C0 vxorps xmm0, xmm0- C5FA7F0424 vmovdqu xmmword ptr [rsp], xmm0- 4889442410 mov qword ptr [rsp+10H], rax
48C7042402000000 mov qword ptr [rsp], 2
G_M25775_IG03:
4883C418 add rsp, 24
C3 ret
-; Total bytes of code 52, prolog size 23, PerfScore 14.27, (MethodHash=0c929b50) for method C:M()+; Total bytes of code 33, prolog size 20, PerfScore 8.58, (MethodHash=0c929b50) for method C:M()Diffs after this change: G_M25775_IG01:
- 4883EC18 sub rsp, 24- C5D857E4 vxorps xmm4, xmm4- C5F97F2424 vmovdqa xmmword ptr [rsp], xmm4- 33C0 xor rax, rax- 4889442410 mov qword ptr [rsp+10H], rax
G_M25775_IG02:
- 48C7042402000000 mov qword ptr [rsp], 2
G_M25775_IG03:
- 4883C418 add rsp, 24
C3 ret
-; Total bytes of code 33, prolog size 20, PerfScore 8.58, (MethodHash=0c929b50) for method C:M()+; Total bytes of code 1, prolog size 0, PerfScore 1.10, (MethodHash=0c929b50) for method C:M() |
erozenfeld
commented
Jun 1, 2020
ContributorAuthor
@dotnet/jit-contrib @CarolEidt PTAL |
This is a follow-up to dotnet#36918. It addresses one of the examples in dotnet#1007 where we remove a struct zero initialization but fail to clean up a dead field assignment. The change is not to mark a dependently promoted field as untracked if we know that the struct local is no longer referenced. I also addressed a couple of late cosmetic review comments from dotnet#36918. No diffs in framework and benchmarks.
erozenfeld
commented
Jun 8, 2020
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I pushed a change that fixes Linux arm test failures. |
CarolEidt
approved these changes
Jun 9, 2020
CarolEidt
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LGTM, with just one question for curiosity's sake.
| } | ||
| // Fields of dependently promoted structs may be tracked. We shouldn't set lvMustInit on them since | ||
| // the whole parent struct will be initialized; however, lvLiveInOutOfHndlr should be set on them | ||
| // as appropriate. |
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If the field is dependently promoted (i.e. the whole struct is forced to live on the stack), then do we still need to mark them as lvLiveInOutOfHndlr since they'll always be defined/used to/from the stack?
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With this change we may enregister a field of a dependently promoted struct if the struct is no longer used. See the change in lclvars.cpp: we don't set lvaSetVarDoNotEnregister on such fields.
CarolEidt added a commit
to CarolEidt/runtime
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Jun 10, 2020
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This is a follow-up to #36918. It addresses one of the examples in #1007
where we remove a struct zero initialization but fail to clean up a dead
field assignment.
The change is not to mark a dependently promoted field as untracked
if we know that the struct local is no longer referenced.
I also addressed a couple of late cosmetic review comments from #36918.
No diffs in framework and benchmarks.