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Canonicalize min/max expressions correctly.
This patch introduces a canonical form for min/max idioms where one operand is extended or truncated. This often happens when the other operand is a constant. For example: %1 = icmp slt i32 %a, i32 0 %2 = sext i32 %a to i64 %3 = select i1 %1, i64 %2, i64 0 Would now be canonicalized into: %1 = icmp slt i32 %a, i32 0 %2 = select i1 %1, i32 %a, i32 0 %3 = sext i32 %2 to i64 This builds upon a patch posted by David Majenemer (https://www.marc.info/?l=llvm-commits&m=143008038714141&w=2). That pass passively stopped instcombine from ruining canonical patterns. This patch additionally actively makes instcombine canonicalize too. Canonicalization of expressions involving a change in type from int->fp or fp->int are not yet implemented. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237453 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -3970,6 +3970,19 @@ Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
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}
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}
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// Test if the FCmpInst instruction is used exclusively by a select as
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// part of a minimum or maximum operation. If so, refrain from doing
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// any other folding. This helps out other analyses which understand
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// non-obfuscated minimum and maximum idioms, such as ScalarEvolution
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// and CodeGen. And in this case, at least one of the comparison
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// operands has at least one user besides the compare (the select),
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// which would often largely negate the benefit of folding anyway.
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if (I.hasOneUse())
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if (SelectInst *SI = dyn_cast<SelectInst>(*I.user_begin()))
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if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) ||
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(SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1))
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return nullptr;
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// Handle fcmp with constant RHS
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if (Constant *RHSC = dyn_cast<Constant>(Op1)) {
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if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
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@ -1154,18 +1154,30 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
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}
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// See if we can fold the select into one of our operands.
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if (SI.getType()->isIntegerTy()) {
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if (SI.getType()->isIntOrIntVectorTy()) {
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if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
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return FoldI;
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Value *LHS, *RHS, *LHS2, *RHS2;
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SelectPatternFlavor SPF = matchSelectPattern(&SI, LHS, RHS);
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Instruction::CastOps CastOp;
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SelectPatternFlavor SPF = matchSelectPattern(&SI, LHS, RHS, &CastOp);
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// MAX(MAX(a, b), a) -> MAX(a, b)
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// MIN(MIN(a, b), a) -> MIN(a, b)
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// MAX(MIN(a, b), a) -> a
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// MIN(MAX(a, b), a) -> a
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if (SPF) {
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// Canonicalize so that type casts are outside select patterns.
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if (LHS->getType()->getPrimitiveSizeInBits() !=
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SI.getType()->getPrimitiveSizeInBits()) {
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CmpInst::Predicate Pred = getICmpPredicateForMinMax(SPF);
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Value *Cmp = Builder->CreateICmp(Pred, LHS, RHS);
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Value *NewSI = Builder->CreateCast(CastOp,
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Builder->CreateSelect(Cmp, LHS, RHS),
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SI.getType());
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return ReplaceInstUsesWith(SI, NewSI);
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}
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// MAX(MAX(a, b), a) -> MAX(a, b)
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// MIN(MIN(a, b), a) -> MIN(a, b)
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// MAX(MIN(a, b), a) -> a
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// MIN(MAX(a, b), a) -> a
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if (SelectPatternFlavor SPF2 = matchSelectPattern(LHS, LHS2, RHS2))
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if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
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SI, SPF, RHS))
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@ -714,6 +714,22 @@ Instruction *InstCombiner::FoldOpIntoSelect(Instruction &Op, SelectInst *SI) {
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return nullptr;
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}
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// Test if a CmpInst instruction is used exclusively by a select as
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// part of a minimum or maximum operation. If so, refrain from doing
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// any other folding. This helps out other analyses which understand
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// non-obfuscated minimum and maximum idioms, such as ScalarEvolution
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// and CodeGen. And in this case, at least one of the comparison
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// operands has at least one user besides the compare (the select),
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// which would often largely negate the benefit of folding anyway.
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if (auto *CI = dyn_cast<CmpInst>(SI->getCondition())) {
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if (CI->hasOneUse()) {
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Value *Op0 = CI->getOperand(0), *Op1 = CI->getOperand(1);
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if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) ||
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(SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1))
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return nullptr;
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}
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}
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Value *SelectTrueVal = FoldOperationIntoSelectOperand(Op, TV, this);
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Value *SelectFalseVal = FoldOperationIntoSelectOperand(Op, FV, this);
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@ -723,7 +739,6 @@ Instruction *InstCombiner::FoldOpIntoSelect(Instruction &Op, SelectInst *SI) {
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return nullptr;
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}
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/// FoldOpIntoPhi - Given a binary operator, cast instruction, or select which
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/// has a PHI node as operand #0, see if we can fold the instruction into the
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/// PHI (which is only possible if all operands to the PHI are constants).
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73
test/Transforms/InstCombine/minmax-fold.ll
Normal file
73
test/Transforms/InstCombine/minmax-fold.ll
Normal file
@ -0,0 +1,73 @@
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; RUN: opt -S -instcombine < %s | FileCheck %s
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; CHECK-LABEL: @t1
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; CHECK-NEXT: icmp
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; CHECK-NEXT: select
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; CHECK-NEXT: sext
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define i64 @t1(i32 %a) {
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; This is the canonical form for a type-changing min/max.
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%1 = icmp slt i32 %a, 5
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%2 = select i1 %1, i32 %a, i32 5
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%3 = sext i32 %2 to i64
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ret i64 %3
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}
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; CHECK-LABEL: @t2
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; CHECK-NEXT: icmp
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; CHECK-NEXT: select
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; CHECK-NEXT: sext
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define i64 @t2(i32 %a) {
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; Check this is converted into canonical form, as above.
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%1 = icmp slt i32 %a, 5
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%2 = sext i32 %a to i64
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%3 = select i1 %1, i64 %2, i64 5
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ret i64 %3
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}
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; CHECK-LABEL: @t3
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; CHECK-NEXT: icmp
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; CHECK-NEXT: select
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; CHECK-NEXT: zext
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define i64 @t3(i32 %a) {
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; Same as @t2, with flipped operands and zext instead of sext.
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%1 = icmp ult i32 %a, 5
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%2 = zext i32 %a to i64
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%3 = select i1 %1, i64 5, i64 %2
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ret i64 %3
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}
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; CHECK-LABEL: @t4
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; CHECK-NEXT: icmp
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; CHECK-NEXT: select
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; CHECK-NEXT: trunc
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define i32 @t4(i64 %a) {
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; Same again, with trunc.
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%1 = icmp slt i64 %a, 5
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%2 = trunc i64 %a to i32
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%3 = select i1 %1, i32 %2, i32 5
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ret i32 %3
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}
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; CHECK-LABEL: @t5
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; CHECK-NEXT: icmp
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; CHECK-NEXT: zext
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; CHECK-NEXT: select
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define i64 @t5(i32 %a) {
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; Same as @t3, but with mismatched signedness between icmp and zext.
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; InstCombine should leave this alone.
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%1 = icmp slt i32 %a, 5
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%2 = zext i32 %a to i64
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%3 = select i1 %1, i64 5, i64 %2
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ret i64 %3
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}
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; CHECK-LABEL: @t6
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; CHECK-NEXT: icmp
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; CHECK-NEXT: select
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; CHECK-NEXT: sitofp
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define float @t6(i32 %a) {
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%1 = icmp slt i32 %a, 0
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%2 = select i1 %1, i32 %a, i32 0
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%3 = sitofp i32 %2 to float
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ret float %3
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}
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