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Do not set branch weight if the branch weight annotation is present. 

Summary: ThinLTO will annotate the CFG twice. If the branch weight is set by the first annotation, we should not set the branch weight again in the second annotation because the first annotation is more accurate as there is less optimization that could affect debug info accuracy.

Reviewers: tejohnson, davidxl

Reviewed By: tejohnson

Subscribers: mehdi_amini, aprantl, llvm-commits

Differential Revision: https://reviews.llvm.org/D31228

llvm-svn: 298602
This commit is contained in:
Dehao Chen 2017-03-23 14:43:10 +00:00
parent 50910bf842
commit 53a0c082d2
2 changed files with 9 additions and 2 deletions
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6
llvm/lib/Transforms/IPO/SampleProfile.cpp
View File

@ -1162,9 +1162,13 @@ void SampleProfileLoader::propagateWeights(Function &F) {
}
}
uint64_t TempWeight;
// Only set weights if there is at least one non-zero weight.
// In any other case, let the analyzer set weights.
if (MaxWeight > 0) {
// Do not set weights if the weights are present. In ThinLTO, the profile
// annotation is done twice. If the first annotation already set the
// weights, the second pass does not need to set it.
if (MaxWeight > 0 && !TI->extractProfTotalWeight(TempWeight)) {
DEBUG(dbgs() << "SUCCESS. Found non-zero weights.\n");
TI->setMetadata(llvm::LLVMContext::MD_prof,
MDB.createBranchWeights(Weights));

5
llvm/test/Transforms/SampleProfile/branch.ll
View File

@ -87,7 +87,9 @@ for.cond: ; preds = %for.inc, %if.then.2
%6 = load i32, i32* %u, align 4, !dbg !46
%7 = load i32, i32* %limit, align 4, !dbg !48
%cmp5 = icmp slt i32 %6, %7, !dbg !49
br i1 %cmp5, label %for.body, label %for.end, !dbg !50
br i1 %cmp5, label %for.body, label %for.end, !dbg !50, !prof !80
; CHECK: edge for.cond -> for.body probability is 0x73333333 / 0x80000000 = 90.00%
; CHECK: edge for.cond -> for.end probability is 0x0ccccccd / 0x80000000 = 10.00%
for.body: ; preds = %for.cond
call void @llvm.dbg.declare(metadata double* %x, metadata !51, metadata !17), !dbg !53
@ -237,3 +239,4 @@ attributes #4 = { nounwind readonly }
!77 = !DILocation(line: 20, column: 4, scope: !6)
!78 = !DILocation(line: 21, column: 4, scope: !6)
!79 = !DILocation(line: 22, column: 2, scope: !6)
!80 = !{!"branch_weights", i32 90, i32 10}