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Propagate branch metadata when some branch probability is missing. 

Summary: In sample profile, some branches may have profile missing due to profile inaccuracy. We want existing branch probability still valid after propagation.

Reviewers: hfinkel, davidxl, spatel

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D19948

llvm-svn: 269137
This commit is contained in:
Dehao Chen 2016-05-10 23:07:19 +00:00
parent 1df01f0e31
commit b76e5d948a
2 changed files with 38 additions and 6 deletions
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18
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -2821,15 +2821,23 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
// Update branch weight for PBI.
uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
uint64_t PredCommon, PredOther, SuccCommon, SuccOther;
bool PredHasWeights =
PBI->extractProfMetadata(PredTrueWeight, PredFalseWeight);
bool SuccHasWeights =
BI->extractProfMetadata(SuccTrueWeight, SuccFalseWeight);
if (PredHasWeights && SuccHasWeights) {
uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight;
uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
bool HasWeights = PredHasWeights || SuccHasWeights;
if (HasWeights) {
if (!PredHasWeights) {
PredFalseWeight = PredTrueWeight = 1;
}
if (!SuccHasWeights) {
SuccFalseWeight = SuccTrueWeight = 1;
}
PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
PredOther = PBIOp ? PredTrueWeight : PredFalseWeight;
SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
// The weight to CommonDest should be PredCommon * SuccTotal +
// PredOther * SuccCommon.
// The weight to OtherDest should be PredOther * SuccOther.

26
llvm/test/Transforms/SimplifyCFG/preserve-branchweights.ll
View File

@ -464,6 +464,30 @@ exit:
ret i32 %outval
}
define i32 @SimplifyCondBranchToCondBranchSwapMissingWeight(i1 %cmpa, i1 %cmpb) {
; CHECK-LABEL: @SimplifyCondBranchToCondBranchSwapMissingWeight(
; CHECK-NEXT: block1:
; CHECK-NEXT: [[CMPA_NOT:%.*]] = xor i1 %cmpa, true
; CHECK-NEXT: [[CMPB_NOT:%.*]] = xor i1 %cmpb, true
; CHECK-NEXT: [[BRMERGE:%.*]] = or i1 [[CMPA_NOT]], [[CMPB_NOT]]
; CHECK-NEXT: [[DOTMUX:%.*]] = select i1 [[CMPA_NOT]], i32 0, i32 2
; CHECK-NEXT: [[OUTVAL:%.*]] = select i1 [[BRMERGE]], i32 [[DOTMUX]], i32 1, !prof !16
; CHECK-NEXT: ret i32 [[OUTVAL]]
;
block1:
br i1 %cmpa, label %block2, label %block3, !prof !13
block2:
br i1 %cmpb, label %exit, label %block3
block3:
%cowval = phi i32 [ 2, %block2 ], [ 0, %block1 ]
br label %exit
exit:
%outval = phi i32 [ %cowval, %block3 ], [ 1, %block2 ]
ret i32 %outval
}
!0 = !{!"branch_weights", i32 3, i32 5}
!1 = !{!"branch_weights", i32 1, i32 1}
@ -499,4 +523,4 @@ exit:
; CHECK: !13 = !{!"branch_weights", i32 34, i32 21}
; CHECK: !14 = !{!"branch_weights", i32 33, i32 14}
; CHECK: !15 = !{!"branch_weights", i32 47, i32 8}
; CHECK: !16 = !{!"branch_weights", i32 8, i32 2}