Make sure if we're truncating a constant that would then be sign extended
that the sign extension of the truncated constant is the same as the
original constant.
> 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@237821
91177308-0d34-0410-b5e6-
96231b3b80d8
return nullptr;
*CastOp = CI->getOpcode();
- if ((isa<SExtInst>(CI) && CmpI->isSigned()) ||
- (isa<ZExtInst>(CI) && CmpI->isUnsigned()))
+ if (isa<SExtInst>(CI) && CmpI->isSigned()) {
+ Constant *T = ConstantExpr::getTrunc(C, CI->getSrcTy());
+ // This is only valid if the truncated value can be sign-extended
+ // back to the original value.
+ if (ConstantExpr::getSExt(T, C->getType()) == C)
+ return T;
+ return nullptr;
+ }
+ if (isa<ZExtInst>(CI) && CmpI->isUnsigned())
return ConstantExpr::getTrunc(C, CI->getSrcTy());
if (isa<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<SelectInst>(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))
}
}
+ // 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<SelectInst>(*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<Constant>(Op1)) {
if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
}
// 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<Instruction>(LHS),SPF2,LHS2,RHS2,
SI, SPF, RHS))
//===----------------------------------------------------------------------===//
#include "InstCombineInternal.h"
+#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
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,
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<CmpInst>(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);
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).
--- /dev/null
+; 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
+}
+
+; Ensure this doesn't get converted to a min/max.
+; CHECK-LABEL: @t9
+; CHECK-NEXT: icmp
+; CHECK-NEXT: sext
+; CHECK-NEXT: 4294967295
+; CHECK-NEXT: ret
+define i64 @t9(i32 %a) {
+ %1 = icmp sgt i32 %a, -1
+ %2 = sext i32 %a to i64
+ %3 = select i1 %1, i64 %2, i64 4294967295
+ ret i64 %3
+}
projects / llvm / commitdiff