From 576f0d9e3e82fc854a80a1b8102adf7b9004cd6c Mon Sep 17 00:00:00 2001 From: Sanjay Patel Date: Fri, 6 May 2016 17:07:47 +0000 Subject: [PATCH] [SimplifyCFG] propagate branch metadata when creating select (retry r268550 with possible fix) Retrying r268550 which was reverted at r268577 due a memory sanitizer failure. I have not been able to reproduce that failure, but I've taken a guess at fixing the problem in this version of the patch and will watch for another failure. Original commit message: Unlike earlier similar fixes, we need to recalculate the branch weights in this case. Differential Revision: http://reviews.llvm.org/D19674 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268751 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Utils/SimplifyCFG.cpp | 33 +++++++++---- .../SimplifyCFG/preserve-branchweights.ll | 47 +++++++++++++++---- 2 files changed, 63 insertions(+), 17 deletions(-) diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp index fe7c609051e..691c59141cf 100644 --- a/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/lib/Transforms/Utils/SimplifyCFG.cpp @@ -848,7 +848,7 @@ static void GetBranchWeights(TerminatorInst *TI, } } -/// Keep halving the weights until all can fit in uint32_t. +/// Scale each weight so they all fit in uint32_t. static void FitWeights(MutableArrayRef Weights) { uint64_t Max = *std::max_element(Weights.begin(), Weights.end()); if (Max > UINT_MAX) { @@ -2820,28 +2820,28 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI, PBI->setSuccessor(1, OtherDest); // Update branch weight for PBI. + MDBuilder MDB(BI->getContext()); 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; + 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. uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther) + PredOther * SuccCommon, PredOther * SuccOther}; - // Halve the weights if any of them cannot fit in an uint32_t FitWeights(NewWeights); PBI->setMetadata(LLVMContext::MD_prof, - MDBuilder(BI->getContext()) - .createBranchWeights(NewWeights[0], NewWeights[1])); + MDB.createBranchWeights(NewWeights[0], NewWeights[1])); } // OtherDest may have phi nodes. If so, add an entry from PBI's @@ -2860,9 +2860,24 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI, Value *PBIV = PN->getIncomingValue(PBBIdx); if (BIV != PBIV) { // Insert a select in PBI to pick the right value. - Value *NV = cast + SelectInst *NV = cast (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName() + ".mux")); PN->setIncomingValue(PBBIdx, NV); + // Although the select has the same condition as PBI, the original branch + // weights for PBI do not apply to the new select because the select's + // 'logical' edges are incoming edges of the phi that is eliminated, not + // the outgoing edges of PBI. + if (PredHasWeights && SuccHasWeights) { + // The weight to PredCommonDest should be PredCommon * SuccTotal. + // The weight to PredOtherDest should be PredOther * SuccCommon. + uint64_t NewWeights[2] = {PredCommon * (SuccCommon + SuccOther), + PredOther * SuccCommon}; + + FitWeights(NewWeights); + + NV->setMetadata(LLVMContext::MD_prof, + MDB.createBranchWeights(NewWeights[0], NewWeights[1])); + } } } diff --git a/test/Transforms/SimplifyCFG/preserve-branchweights.ll b/test/Transforms/SimplifyCFG/preserve-branchweights.ll index ae32809395e..359f21a75ab 100644 --- a/test/Transforms/SimplifyCFG/preserve-branchweights.ll +++ b/test/Transforms/SimplifyCFG/preserve-branchweights.ll @@ -412,22 +412,48 @@ return: ret i32 %retval.0 } -; The 1st select should have branch weights equal to the 1st branch. -; The 2nd select should have freshly calculated branch weights. +; The selects should have freshly calculated branch weights. define i32 @SimplifyCondBranchToCondBranch(i1 %cmpa, i1 %cmpb) { ; CHECK-LABEL: @SimplifyCondBranchToCondBranch( ; CHECK-NEXT: block1: -; CHECK-NEXT: [[BRMERGE:%.*]] = or i1 %cmpb, %cmpa -; CHECK-NEXT: [[DOTMUX:%.*]] = select i1 %cmpb, i32 0, i32 2 -; CHECK-NEXT: [[OUTVAL:%.*]] = select i1 [[BRMERGE]], i32 [[DOTMUX]], i32 1, !prof !12 +; CHECK-NEXT: [[BRMERGE:%.*]] = or i1 %cmpa, %cmpb +; CHECK-NEXT: [[DOTMUX:%.*]] = select i1 %cmpa, i32 0, i32 2, !prof !12 +; CHECK-NEXT: [[OUTVAL:%.*]] = select i1 [[BRMERGE]], i32 [[DOTMUX]], i32 1, !prof !13 ; CHECK-NEXT: ret i32 [[OUTVAL]] ; block1: - br i1 %cmpb, label %block3, label %block2, !prof !0 + br i1 %cmpa, label %block3, label %block2, !prof !13 block2: - br i1 %cmpa, label %block3, label %exit, !prof !2 + br i1 %cmpb, label %block3, label %exit, !prof !14 + +block3: + %cowval = phi i32 [ 2, %block2 ], [ 0, %block1 ] + br label %exit + +exit: + %outval = phi i32 [ %cowval, %block3 ], [ 1, %block2 ] + ret i32 %outval +} + +; Swap the operands of the compares to verify that the weights update correctly. + +define i32 @SimplifyCondBranchToCondBranchSwap(i1 %cmpa, i1 %cmpb) { +; CHECK-LABEL: @SimplifyCondBranchToCondBranchSwap( +; 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, !prof !14 +; CHECK-NEXT: [[OUTVAL:%.*]] = select i1 [[BRMERGE]], i32 [[DOTMUX]], i32 1, !prof !15 +; CHECK-NEXT: ret i32 [[OUTVAL]] +; +block1: + br i1 %cmpa, label %block2, label %block3, !prof !13 + +block2: + br i1 %cmpb, label %exit, label %block3, !prof !14 block3: %cowval = phi i32 [ 2, %block2 ], [ 0, %block1 ] @@ -452,6 +478,8 @@ exit: !10 = !{!"branch_weights", i32 672646, i32 21604207} !11 = !{!"branch_weights", i32 6960, i32 21597248} !12 = !{!"these_are_not_the_branch_weights_you_are_looking_for", i32 3, i32 5} +!13 = !{!"branch_weights", i32 2, i32 3} +!14 = !{!"branch_weights", i32 4, i32 7} ; CHECK: !0 = !{!"branch_weights", i32 5, i32 11} ; CHECK: !1 = !{!"branch_weights", i32 1, i32 5} @@ -467,5 +495,8 @@ exit: ;; treat the weight as an unsigned integer. ; CHECK: !10 = !{!"branch_weights", i32 112017436, i32 -735157296} ; CHECK: !11 = !{!"branch_weights", i32 3, i32 5} -; CHECK: !12 = !{!"branch_weights", i32 14, i32 10} +; CHECK: !12 = !{!"branch_weights", i32 22, i32 12} +; CHECK: !13 = !{!"branch_weights", i32 34, i32 21} +; CHECK: !14 = !{!"branch_weights", i32 33, i32 14} +; CHECK: !15 = !{!"branch_weights", i32 47, i32 8} -- 2.50.1