From 288b81996cbc261ae60fb92c7b55865bee588a4a Mon Sep 17 00:00:00 2001 From: Sanjay Patel Date: Wed, 8 Apr 2020 08:54:28 -0400 Subject: [PATCH] [InstCombine] exclude bitcast of ppc_fp128 in icmp signbit fold Based on the post-commit comments for rG0f56bbc, there might be a problem with this transform: (bitcast (fpext/fptrunc X)) to iX) < 0 --> (bitcast X to iY) < 0 ...and the ppc_fp128 data type, so conservatively bypass if we are bitcasting a ppc_fp128. We might be able to account for endian or other differences to enable this for PowerPC again if that is useful. Differential Revision: https://reviews.llvm.org/D77642 --- lib/Transforms/InstCombine/InstCombineCompares.cpp | 8 +++++--- test/Transforms/InstCombine/icmp.ll | 5 +++-- 2 files changed, 8 insertions(+), 5 deletions(-) diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp index bb7d0c93075..e1e262821ef 100644 --- a/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -2763,11 +2763,13 @@ static Instruction *foldICmpBitCast(ICmpInst &Cmp, return new ICmpInst(Pred, X, ConstantInt::getNullValue(X->getType())); // If this is a sign-bit test of a bitcast of a casted FP value, eliminate - // the FP cast because the FP cast does not change the sign-bit. + // the FP extend/truncate because that cast does not change the sign-bit. + // This is true for all standard IEEE-754 types and the X86 80-bit type. + // The sign-bit is always the most significant bit in those types. const APInt *C; bool TrueIfSigned; - if (match(Op1, m_APInt(C)) && Bitcast->hasOneUse() && - isSignBitCheck(Pred, *C, TrueIfSigned)) { + if (!BCSrcOp->getType()->isPPC_FP128Ty() && match(Op1, m_APInt(C)) && + Bitcast->hasOneUse() && isSignBitCheck(Pred, *C, TrueIfSigned)) { if (match(BCSrcOp, m_FPExt(m_Value(X))) || match(BCSrcOp, m_FPTrunc(m_Value(X)))) { // (bitcast (fpext/fptrunc X)) to iX) < 0 --> (bitcast X to iY) < 0 diff --git a/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll index 2da5c696d04..96673eb9e45 100644 --- a/test/Transforms/InstCombine/icmp.ll +++ b/test/Transforms/InstCombine/icmp.ll @@ -3700,8 +3700,9 @@ define i1 @signbit_bitcast_fpext_extra_use(float %x, i64* %p) { define i1 @signbit_bitcast_fpext_ppc_fp128(float %x) { ; CHECK-LABEL: @signbit_bitcast_fpext_ppc_fp128( -; CHECK-NEXT: [[TMP1:%.*]] = bitcast float [[X:%.*]] to i32 -; CHECK-NEXT: [[S4:%.*]] = icmp slt i32 [[TMP1]], 0 +; CHECK-NEXT: [[S2:%.*]] = fpext float [[X:%.*]] to ppc_fp128 +; CHECK-NEXT: [[S3:%.*]] = bitcast ppc_fp128 [[S2]] to i128 +; CHECK-NEXT: [[S4:%.*]] = icmp slt i128 [[S3]], 0 ; CHECK-NEXT: ret i1 [[S4]] ; %s2 = fpext float %x to ppc_fp128