From 5d7d689edf01e41d908ced188efcc6405627fd2b Mon Sep 17 00:00:00 2001 From: Sanjay Patel Date: Tue, 31 Aug 2021 09:42:13 -0400 Subject: [PATCH] [InstCombine] fix propagation of FMF through select-of-fnegs The existing code was unquestionably wrong - it looked at one fneg and ignored the other 2 instructions. It was also untested, so it didn't make the list of bugs flagged by Alive2. This is an unusual propagation, but Alive2 agress that we can intersect the fnegs and union that with the select, then apply the results to both new instructions: https://alive2.llvm.org/ce/z/SF8_dt --- llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp | 10 +++++++++- llvm/test/Transforms/InstCombine/fneg.ll | 14 +++++++------- 2 files changed, 16 insertions(+), 8 deletions(-) diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp index ff4611e..b9242f4 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp @@ -319,8 +319,16 @@ Instruction *InstCombinerImpl::foldSelectOpOp(SelectInst &SI, Instruction *TI, Value *X, *Y; if (match(TI, m_FNeg(m_Value(X))) && match(FI, m_FNeg(m_Value(Y))) && (TI->hasOneUse() || FI->hasOneUse())) { + // Intersect FMF from the fneg instructions and union those with the select. + FastMathFlags FMF = TI->getFastMathFlags(); + FMF &= FI->getFastMathFlags(); + FMF |= SI.getFastMathFlags(); Value *NewSel = Builder.CreateSelect(Cond, X, Y, SI.getName() + ".v", &SI); - return UnaryOperator::CreateFNegFMF(NewSel, TI); + if (auto *NewSelI = dyn_cast(NewSel)) + NewSelI->setFastMathFlags(FMF); + Instruction *NewFNeg = UnaryOperator::CreateFNeg(NewSel); + NewFNeg->setFastMathFlags(FMF); + return NewFNeg; } // Min/max intrinsic with a common operand can have the common operand pulled diff --git a/llvm/test/Transforms/InstCombine/fneg.ll b/llvm/test/Transforms/InstCombine/fneg.ll index 9caa620..3e1d581 100644 --- a/llvm/test/Transforms/InstCombine/fneg.ll +++ b/llvm/test/Transforms/InstCombine/fneg.ll @@ -441,7 +441,7 @@ define float @fneg_fneg_sel_extra_use3(float %x, float %y, i1 %cond) { define double @fneg_fneg_sel_fmf1(double %x, double %y, i1 %cond) { ; CHECK-LABEL: @fneg_fneg_sel_fmf1( ; CHECK-NEXT: [[SEL_V:%.*]] = select i1 [[COND:%.*]], double [[X:%.*]], double [[Y:%.*]] -; CHECK-NEXT: [[SEL:%.*]] = fneg nnan double [[SEL_V]] +; CHECK-NEXT: [[SEL:%.*]] = fneg double [[SEL_V]] ; CHECK-NEXT: ret double [[SEL]] ; %n1 = fneg nnan double %x @@ -452,8 +452,8 @@ define double @fneg_fneg_sel_fmf1(double %x, double %y, i1 %cond) { define double @fneg_fneg_sel_fmf2(double %x, double %y, i1 %cond) { ; CHECK-LABEL: @fneg_fneg_sel_fmf2( -; CHECK-NEXT: [[SEL_V:%.*]] = select i1 [[COND:%.*]], double [[X:%.*]], double [[Y:%.*]] -; CHECK-NEXT: [[SEL:%.*]] = fneg nnan ninf double [[SEL_V]] +; CHECK-NEXT: [[SEL_V:%.*]] = select ninf i1 [[COND:%.*]], double [[X:%.*]], double [[Y:%.*]] +; CHECK-NEXT: [[SEL:%.*]] = fneg ninf double [[SEL_V]] ; CHECK-NEXT: ret double [[SEL]] ; %n1 = fneg nnan ninf double %x @@ -464,8 +464,8 @@ define double @fneg_fneg_sel_fmf2(double %x, double %y, i1 %cond) { define double @fneg_fneg_sel_fmf3(double %x, double %y, i1 %cond) { ; CHECK-LABEL: @fneg_fneg_sel_fmf3( -; CHECK-NEXT: [[SEL_V:%.*]] = select i1 [[COND:%.*]], double [[X:%.*]], double [[Y:%.*]] -; CHECK-NEXT: [[SEL:%.*]] = fneg nnan ninf double [[SEL_V]] +; CHECK-NEXT: [[SEL_V:%.*]] = select ninf i1 [[COND:%.*]], double [[X:%.*]], double [[Y:%.*]] +; CHECK-NEXT: [[SEL:%.*]] = fneg ninf double [[SEL_V]] ; CHECK-NEXT: ret double [[SEL]] ; %n1 = fneg nnan ninf double %x @@ -476,8 +476,8 @@ define double @fneg_fneg_sel_fmf3(double %x, double %y, i1 %cond) { define double @fneg_fneg_sel_fmf4(double %x, double %y, i1 %cond) { ; CHECK-LABEL: @fneg_fneg_sel_fmf4( -; CHECK-NEXT: [[SEL_V:%.*]] = select i1 [[COND:%.*]], double [[X:%.*]], double [[Y:%.*]] -; CHECK-NEXT: [[SEL:%.*]] = fneg nnan double [[SEL_V]] +; CHECK-NEXT: [[SEL_V:%.*]] = select nnan ninf nsz i1 [[COND:%.*]], double [[X:%.*]], double [[Y:%.*]] +; CHECK-NEXT: [[SEL:%.*]] = fneg nnan ninf nsz double [[SEL_V]] ; CHECK-NEXT: ret double [[SEL]] ; %n1 = fneg nnan double %x -- 2.7.4