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Only set branch weight during sample pgo annotation when max_weight of the branch is non-zero. Otherwise use default static profile to set branch probability.

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Summary: It does not make sense to set equal weights for all unkown branches as we have static branch prediction available.

Reviewers: dnovillo

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D24732

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@281912 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dehao Chen 2016-09-19 16:33:41 +00:00
parent 625183db5a
commit ba3d957955
2 changed files with 20 additions and 19 deletions
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26
lib/Transforms/IPO/SampleProfile.cpp
View File

@ -1120,17 +1120,21 @@ void SampleProfileLoader::propagateWeights(Function &F) {
// Only set weights if there is at least one non-zero weight.
// In any other case, let the analyzer set weights.
DEBUG(dbgs() << "SUCCESS. Found non-zero weights.\n");
TI->setMetadata(llvm::LLVMContext::MD_prof,
MDB.createBranchWeights(Weights));
DebugLoc BranchLoc = TI->getDebugLoc();
emitOptimizationRemark(
Ctx, DEBUG_TYPE, F, MaxDestLoc,
Twine("most popular destination for conditional branches at ") +
((BranchLoc) ? Twine(BranchLoc->getFilename() + ":" +
Twine(BranchLoc.getLine()) + ":" +
Twine(BranchLoc.getCol()))
: Twine("<UNKNOWN LOCATION>")));
if (MaxWeight > 0) {
DEBUG(dbgs() << "SUCCESS. Found non-zero weights.\n");
TI->setMetadata(llvm::LLVMContext::MD_prof,
MDB.createBranchWeights(Weights));
DebugLoc BranchLoc = TI->getDebugLoc();
emitOptimizationRemark(
Ctx, DEBUG_TYPE, F, MaxDestLoc,
Twine("most popular destination for conditional branches at ") +
((BranchLoc) ? Twine(BranchLoc->getFilename() + ":" +
Twine(BranchLoc.getLine()) + ":" +
Twine(BranchLoc.getCol()))
: Twine("<UNKNOWN LOCATION>")));
} else {
DEBUG(dbgs() << "SKIPPED. All branch weights are zero.\n");
}
}
}

13
test/Transforms/SampleProfile/fnptr.ll
View File

@ -12,8 +12,8 @@
; CHECK: edge for.body3 -> if.else probability is 0x65a95a96 / 0x80000000 = 79.42%
; CHECK: edge for.inc -> for.inc12 probability is 0x000fdc50 / 0x80000000 = 0.05%
; CHECK: edge for.inc -> for.body3 probability is 0x7ff023b0 / 0x80000000 = 99.95%
; CHECK: edge for.inc12 -> for.end14 probability is 0x40000000 / 0x80000000 = 50.00%
; CHECK: edge for.inc12 -> for.cond1.preheader probability is 0x40000000 / 0x80000000 = 50.00%
; CHECK: edge for.inc12 -> for.end14 probability is 0x04000000 / 0x80000000 = 3.12%
; CHECK: edge for.inc12 -> for.cond1.preheader probability is 0x7c000000 / 0x80000000 = 96.88%
; Original C++ test case.
;
@ -88,7 +88,7 @@ for.body3: ; preds = %for.inc, %for.cond1
%call5 = tail call i32 @rand() #3, !dbg !16
%rem6 = srem i32 %call5, 100, !dbg !16
%cmp7 = icmp slt i32 %rem6, 10, !dbg !16
br i1 %cmp7, label %if.then, label %if.else, !dbg !16, !prof !17
br i1 %cmp7, label %if.then, label %if.else, !dbg !16
if.then: ; preds = %for.body3
%mul = mul nsw i32 %j.023, 300, !dbg !18
@ -107,13 +107,13 @@ for.inc: ; preds = %if.then, %if.else
%S.2 = fadd double %S.122, %call8.pn, !dbg !18
%inc = add nsw i32 %j.023, 1, !dbg !20
%exitcond = icmp eq i32 %j.023, 5999, !dbg !14
br i1 %exitcond, label %for.inc12, label %for.body3, !dbg !14, !prof !21
br i1 %exitcond, label %for.inc12, label %for.body3, !dbg !14
for.inc12: ; preds = %for.inc
%S.2.lcssa = phi double [ %S.2, %for.inc ]
%inc13 = add nsw i32 %i.025, 1, !dbg !22
%exitcond26 = icmp eq i32 %i.025, 9999, !dbg !12
br i1 %exitcond26, label %for.end14, label %for.cond1.preheader, !dbg !12, !prof !23
br i1 %exitcond26, label %for.end14, label %for.cond1.preheader, !dbg !12
for.end14: ; preds = %for.inc12
%S.2.lcssa.lcssa = phi double [ %S.2.lcssa, %for.inc12 ]
@ -148,13 +148,10 @@ declare i32 @printf(i8* nocapture readonly, ...) #1
!14 = !DILocation(line: 20, column: 5, scope: !13)
!15 = !DILocation(line: 21, column: 15, scope: !13)
!16 = !DILocation(line: 22, column: 11, scope: !13)
!17 = !{!"branch_weights", i32 534, i32 2064}
!18 = !DILocation(line: 23, column: 14, scope: !13)
!19 = !DILocation(line: 25, column: 14, scope: !13)
!20 = !DILocation(line: 20, column: 28, scope: !13)
!21 = !{!"branch_weights", i32 0, i32 1075}
!22 = !DILocation(line: 19, column: 26, scope: !13)
!23 = !{!"branch_weights", i32 0, i32 534}
!24 = !DILocation(line: 27, column: 3, scope: !13)
!25 = !DILocation(line: 28, column: 3, scope: !13)
!26 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, producer: "clang version 3.5 ", isOptimized: false, emissionKind: FullDebug, file: !4)