Author: Yingwei Zheng Date: 2024-05-16T11:42:50-07:00 New Revision: 26ccc6b5c1c73a92e5d08299065709e1d163b6c2
URL: https://github.com/llvm/llvm-project/commit/26ccc6b5c1c73a92e5d08299065709e1d163b6c2 DIFF: https://github.com/llvm/llvm-project/commit/26ccc6b5c1c73a92e5d08299065709e1d163b6c2.diff LOG: [InstCombine] Drop nuw flag when CtlzOp is a sub nuw (#91776) See the following case: ``` define i32 @src1(i32 %x) { %dec = sub nuw i32 -2, %x %ctlz = tail call i32 @llvm.ctlz.i32(i32 %dec, i1 false) %sub = sub nsw i32 32, %ctlz %shl = shl i32 1, %sub %ugt = icmp ult i32 %x, -2 %sel = select i1 %ugt, i32 %shl, i32 1 ret i32 %sel } define i32 @tgt1(i32 %x) { %dec = sub nuw i32 -2, %x %ctlz = tail call i32 @llvm.ctlz.i32(i32 %dec, i1 false) %sub = sub nsw i32 32, %ctlz %and = and i32 %sub, 31 %shl = shl nuw i32 1, %and ret i32 %shl } ``` `nuw` in `%dec` should be dropped after the select instruction is eliminated. Alive2: https://alive2.llvm.org/ce/z/7S9529 Fixes https://github.com/llvm/llvm-project/issues/91691. (cherry picked from commit b5f4210e9f51f938ae517f219f04f9ab431a2684) Added: Modified: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp llvm/test/Transforms/InstCombine/bit_ceil.ll Removed: ################################################################################ diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp index 8cc7901cbac7f..86a39cf2ee93f 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp @@ -3201,7 +3201,8 @@ Instruction *InstCombinerImpl::foldSelectOfBools(SelectInst &SI) { // pattern. static bool isSafeToRemoveBitCeilSelect(ICmpInst::Predicate Pred, Value *Cond0, const APInt *Cond1, Value *CtlzOp, - unsigned BitWidth) { + unsigned BitWidth, + bool &ShouldDropNUW) { // The challenge in recognizing std::bit_ceil(X) is that the operand is used // for the CTLZ proper and select condition, each possibly with some // operation like add and sub. @@ -3224,6 +3225,8 @@ static bool isSafeToRemoveBitCeilSelect(ICmpInst::Predicate Pred, Value *Cond0, ConstantRange CR = ConstantRange::makeExactICmpRegion( CmpInst::getInversePredicate(Pred), *Cond1); + ShouldDropNUW = false; + // Match the operation that's used to compute CtlzOp from CommonAncestor. If // CtlzOp == CommonAncestor, return true as no operation is needed. If a // match is found, execute the operation on CR, update CR, and return true. @@ -3237,6 +3240,7 @@ static bool isSafeToRemoveBitCeilSelect(ICmpInst::Predicate Pred, Value *Cond0, return true; } if (match(CtlzOp, m_Sub(m_APInt(C), m_Specific(CommonAncestor)))) { + ShouldDropNUW = true; CR = ConstantRange(*C).sub(CR); return true; } @@ -3306,14 +3310,20 @@ static Instruction *foldBitCeil(SelectInst &SI, IRBuilderBase &Builder) { Pred = CmpInst::getInversePredicate(Pred); } + bool ShouldDropNUW; + if (!match(FalseVal, m_One()) || !match(TrueVal, m_OneUse(m_Shl(m_One(), m_OneUse(m_Sub(m_SpecificInt(BitWidth), m_Value(Ctlz)))))) || !match(Ctlz, m_Intrinsic<Intrinsic::ctlz>(m_Value(CtlzOp), m_Zero())) || - !isSafeToRemoveBitCeilSelect(Pred, Cond0, Cond1, CtlzOp, BitWidth)) + !isSafeToRemoveBitCeilSelect(Pred, Cond0, Cond1, CtlzOp, BitWidth, + ShouldDropNUW)) return nullptr; + if (ShouldDropNUW) + cast<Instruction>(CtlzOp)->setHasNoUnsignedWrap(false); + // Build 1 << (-CTLZ & (BitWidth-1)). The negation likely corresponds to a // single hardware instruction as opposed to BitWidth - CTLZ, where BitWidth // is an integer constant. Masking with BitWidth-1 comes free on some diff --git a/llvm/test/Transforms/InstCombine/bit_ceil.ll b/llvm/test/Transforms/InstCombine/bit_ceil.ll index 52e70c78ba542..63a5ae012eeb6 100644 --- a/llvm/test/Transforms/InstCombine/bit_ceil.ll +++ b/llvm/test/Transforms/InstCombine/bit_ceil.ll @@ -284,6 +284,42 @@ define <4 x i32> @bit_ceil_v4i32(<4 x i32> %x) { ret <4 x i32> %sel } +define i32 @pr91691(i32 %0) { +; CHECK-LABEL: @pr91691( +; CHECK-NEXT: [[TMP2:%.*]] = sub i32 -2, [[TMP0:%.*]] +; CHECK-NEXT: [[TMP3:%.*]] = tail call range(i32 0, 33) i32 @llvm.ctlz.i32(i32 [[TMP2]], i1 false) +; CHECK-NEXT: [[TMP4:%.*]] = sub nsw i32 0, [[TMP3]] +; CHECK-NEXT: [[TMP5:%.*]] = and i32 [[TMP4]], 31 +; CHECK-NEXT: [[TMP6:%.*]] = shl nuw i32 1, [[TMP5]] +; CHECK-NEXT: ret i32 [[TMP6]] +; + %2 = sub nuw i32 -2, %0 + %3 = tail call i32 @llvm.ctlz.i32(i32 %2, i1 false) + %4 = sub i32 32, %3 + %5 = shl i32 1, %4 + %6 = icmp ult i32 %0, -2 + %7 = select i1 %6, i32 %5, i32 1 + ret i32 %7 +} + +define i32 @pr91691_keep_nsw(i32 %0) { +; CHECK-LABEL: @pr91691_keep_nsw( +; CHECK-NEXT: [[TMP2:%.*]] = sub nsw i32 -2, [[TMP0:%.*]] +; CHECK-NEXT: [[TMP3:%.*]] = tail call range(i32 0, 33) i32 @llvm.ctlz.i32(i32 [[TMP2]], i1 false) +; CHECK-NEXT: [[TMP4:%.*]] = sub nsw i32 0, [[TMP3]] +; CHECK-NEXT: [[TMP5:%.*]] = and i32 [[TMP4]], 31 +; CHECK-NEXT: [[TMP6:%.*]] = shl nuw i32 1, [[TMP5]] +; CHECK-NEXT: ret i32 [[TMP6]] +; + %2 = sub nsw i32 -2, %0 + %3 = tail call i32 @llvm.ctlz.i32(i32 %2, i1 false) + %4 = sub i32 32, %3 + %5 = shl i32 1, %4 + %6 = icmp ult i32 %0, -2 + %7 = select i1 %6, i32 %5, i32 1 + ret i32 %7 +} + declare i32 @llvm.ctlz.i32(i32, i1 immarg) declare i64 @llvm.ctlz.i64(i64, i1 immarg) declare <4 x i32> @llvm.ctlz.v4i32(<4 x i32>, i1) _______________________________________________ llvm-branch-commits mailing list llvm-branch-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
