From 2bb2ea810545e8a051a8e7b3fd2b27ed92ff4b24 Mon Sep 17 00:00:00 2001 From: James Molloy Date: Sun, 17 May 2015 08:27:27 +0000 Subject: [PATCH] Reapply r237520 with another fix for infinite looping SimplifyDemandedBits was "simplifying" a constant by removing just sign bits. This caused a canonicalization race between different parts of instcombine. Fix and regression test added - third time lucky? git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237539 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../InstCombine/InstCombineCasts.cpp | 9 ++ .../InstCombine/InstCombineCompares.cpp | 13 +++ .../InstCombine/InstCombineSelect.cpp | 24 +++-- .../InstCombineSimplifyDemanded.cpp | 7 ++ .../InstCombine/InstructionCombining.cpp | 17 +++- test/Transforms/InstCombine/minmax-fold.ll | 99 +++++++++++++++++++ 6 files changed, 162 insertions(+), 7 deletions(-) create mode 100644 test/Transforms/InstCombine/minmax-fold.ll diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp index 9c2bc34f678..48ab0eb2c1b 100644 --- a/lib/Transforms/InstCombine/InstCombineCasts.cpp +++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp @@ -435,6 +435,15 @@ Instruction *InstCombiner::visitTrunc(TruncInst &CI) { if (Instruction *Result = commonCastTransforms(CI)) return Result; + // Test if the trunc is the user of a select which is part of a + // minimum or maximum operation. If so, don't do any more simplification. + // Even simplifying demanded bits can break the canonical form of a + // min/max. + Value *LHS, *RHS; + if (SelectInst *SI = dyn_cast(CI.getOperand(0))) + if (matchSelectPattern(SI, LHS, RHS) != SPF_UNKNOWN) + return nullptr; + // See if we can simplify any instructions used by the input whose sole // purpose is to compute bits we don't care about. if (SimplifyDemandedInstructionBits(CI)) diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp index 223bba03507..482768655bd 100644 --- a/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -3970,6 +3970,19 @@ Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) { } } + // Test if the FCmpInst instruction is used exclusively by a select as + // part of a minimum or maximum operation. If so, refrain from doing + // any other folding. This helps out other analyses which understand + // non-obfuscated minimum and maximum idioms, such as ScalarEvolution + // and CodeGen. And in this case, at least one of the comparison + // operands has at least one user besides the compare (the select), + // which would often largely negate the benefit of folding anyway. + if (I.hasOneUse()) + if (SelectInst *SI = dyn_cast(*I.user_begin())) + if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) || + (SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1)) + return nullptr; + // Handle fcmp with constant RHS if (Constant *RHSC = dyn_cast(Op1)) { if (Instruction *LHSI = dyn_cast(Op0)) diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp index b13d3edb9ad..d2fbcdd3991 100644 --- a/lib/Transforms/InstCombine/InstCombineSelect.cpp +++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp @@ -1154,18 +1154,30 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) { } // See if we can fold the select into one of our operands. - if (SI.getType()->isIntegerTy()) { + if (SI.getType()->isIntOrIntVectorTy()) { if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal)) return FoldI; Value *LHS, *RHS, *LHS2, *RHS2; - SelectPatternFlavor SPF = matchSelectPattern(&SI, LHS, RHS); + Instruction::CastOps CastOp; + SelectPatternFlavor SPF = matchSelectPattern(&SI, LHS, RHS, &CastOp); - // MAX(MAX(a, b), a) -> MAX(a, b) - // MIN(MIN(a, b), a) -> MIN(a, b) - // MAX(MIN(a, b), a) -> a - // MIN(MAX(a, b), a) -> a if (SPF) { + // Canonicalize so that type casts are outside select patterns. + if (LHS->getType()->getPrimitiveSizeInBits() != + SI.getType()->getPrimitiveSizeInBits()) { + CmpInst::Predicate Pred = getICmpPredicateForMinMax(SPF); + Value *Cmp = Builder->CreateICmp(Pred, LHS, RHS); + Value *NewSI = Builder->CreateCast(CastOp, + Builder->CreateSelect(Cmp, LHS, RHS), + SI.getType()); + return ReplaceInstUsesWith(SI, NewSI); + } + + // MAX(MAX(a, b), a) -> MAX(a, b) + // MIN(MIN(a, b), a) -> MIN(a, b) + // MAX(MIN(a, b), a) -> a + // MIN(MAX(a, b), a) -> a if (SelectPatternFlavor SPF2 = matchSelectPattern(LHS, LHS2, RHS2)) if (Instruction *R = FoldSPFofSPF(cast(LHS),SPF2,LHS2,RHS2, SI, SPF, RHS)) diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp index 955776e0f85..80628b23f11 100644 --- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp +++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp @@ -13,6 +13,7 @@ //===----------------------------------------------------------------------===// #include "InstCombineInternal.h" +#include "llvm/Analysis/ValueTracking.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/PatternMatch.h" @@ -406,6 +407,12 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask, break; } case Instruction::Select: + // If this is a select as part of a min/max pattern, don't simplify any + // further in case we break the structure. + Value *LHS, *RHS; + if (matchSelectPattern(I, LHS, RHS) != SPF_UNKNOWN) + return nullptr; + if (SimplifyDemandedBits(I->getOperandUse(2), DemandedMask, RHSKnownZero, RHSKnownOne, Depth + 1) || SimplifyDemandedBits(I->getOperandUse(1), DemandedMask, LHSKnownZero, diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp index 53ab81dbef2..b0604534150 100644 --- a/lib/Transforms/InstCombine/InstructionCombining.cpp +++ b/lib/Transforms/InstCombine/InstructionCombining.cpp @@ -714,6 +714,22 @@ Instruction *InstCombiner::FoldOpIntoSelect(Instruction &Op, SelectInst *SI) { return nullptr; } + // Test if a CmpInst instruction is used exclusively by a select as + // part of a minimum or maximum operation. If so, refrain from doing + // any other folding. This helps out other analyses which understand + // non-obfuscated minimum and maximum idioms, such as ScalarEvolution + // and CodeGen. And in this case, at least one of the comparison + // operands has at least one user besides the compare (the select), + // which would often largely negate the benefit of folding anyway. + if (auto *CI = dyn_cast(SI->getCondition())) { + if (CI->hasOneUse()) { + Value *Op0 = CI->getOperand(0), *Op1 = CI->getOperand(1); + if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) || + (SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1)) + return nullptr; + } + } + Value *SelectTrueVal = FoldOperationIntoSelectOperand(Op, TV, this); Value *SelectFalseVal = FoldOperationIntoSelectOperand(Op, FV, this); @@ -723,7 +739,6 @@ Instruction *InstCombiner::FoldOpIntoSelect(Instruction &Op, SelectInst *SI) { return nullptr; } - /// FoldOpIntoPhi - Given a binary operator, cast instruction, or select which /// has a PHI node as operand #0, see if we can fold the instruction into the /// PHI (which is only possible if all operands to the PHI are constants). diff --git a/test/Transforms/InstCombine/minmax-fold.ll b/test/Transforms/InstCombine/minmax-fold.ll new file mode 100644 index 00000000000..537251109d9 --- /dev/null +++ b/test/Transforms/InstCombine/minmax-fold.ll @@ -0,0 +1,99 @@ +; RUN: opt -S -instcombine < %s | FileCheck %s + +; CHECK-LABEL: @t1 +; CHECK-NEXT: icmp +; CHECK-NEXT: select +; CHECK-NEXT: sext +define i64 @t1(i32 %a) { + ; This is the canonical form for a type-changing min/max. + %1 = icmp slt i32 %a, 5 + %2 = select i1 %1, i32 %a, i32 5 + %3 = sext i32 %2 to i64 + ret i64 %3 +} + +; CHECK-LABEL: @t2 +; CHECK-NEXT: icmp +; CHECK-NEXT: select +; CHECK-NEXT: sext +define i64 @t2(i32 %a) { + ; Check this is converted into canonical form, as above. + %1 = icmp slt i32 %a, 5 + %2 = sext i32 %a to i64 + %3 = select i1 %1, i64 %2, i64 5 + ret i64 %3 +} + +; CHECK-LABEL: @t3 +; CHECK-NEXT: icmp +; CHECK-NEXT: select +; CHECK-NEXT: zext +define i64 @t3(i32 %a) { + ; Same as @t2, with flipped operands and zext instead of sext. + %1 = icmp ult i32 %a, 5 + %2 = zext i32 %a to i64 + %3 = select i1 %1, i64 5, i64 %2 + ret i64 %3 +} + +; CHECK-LABEL: @t4 +; CHECK-NEXT: icmp +; CHECK-NEXT: select +; CHECK-NEXT: trunc +define i32 @t4(i64 %a) { + ; Same again, with trunc. + %1 = icmp slt i64 %a, 5 + %2 = trunc i64 %a to i32 + %3 = select i1 %1, i32 %2, i32 5 + ret i32 %3 +} + +; CHECK-LABEL: @t5 +; CHECK-NEXT: icmp +; CHECK-NEXT: zext +; CHECK-NEXT: select +define i64 @t5(i32 %a) { + ; Same as @t3, but with mismatched signedness between icmp and zext. + ; InstCombine should leave this alone. + %1 = icmp slt i32 %a, 5 + %2 = zext i32 %a to i64 + %3 = select i1 %1, i64 5, i64 %2 + ret i64 %3 +} + +; CHECK-LABEL: @t6 +; CHECK-NEXT: icmp +; CHECK-NEXT: select +; CHECK-NEXT: sitofp +define float @t6(i32 %a) { + %1 = icmp slt i32 %a, 0 + %2 = select i1 %1, i32 %a, i32 0 + %3 = sitofp i32 %2 to float + ret float %3 +} + +; CHECK-LABEL: @t7 +; CHECK-NEXT: icmp +; CHECK-NEXT: select +; CHECK-NEXT: trunc +define i16 @t7(i32 %a) { + %1 = icmp slt i32 %a, -32768 + %2 = trunc i32 %a to i16 + %3 = select i1 %1, i16 %2, i16 -32768 + ret i16 %3 +} + +; Just check for no infinite loop. InstSimplify liked to +; "simplify" -32767 by removing all the sign bits, +; which led to a canonicalization fight between different +; parts of instcombine. +define i32 @t8(i64 %a, i32 %b) { + %1 = icmp slt i64 %a, -32767 + %2 = select i1 %1, i64 %a, i64 -32767 + %3 = trunc i64 %2 to i32 + %4 = icmp slt i32 %b, 42 + %5 = select i1 %4, i32 42, i32 %3 + %6 = icmp ne i32 %5, %b + %7 = zext i1 %6 to i32 + ret i32 %7 +} -- 2.40.0