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Reapply r237539 with a fix for the Chromium build. 

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.

llvm-svn: 237821
This commit is contained in:
James Molloy 2015-05-20 18:41:25 +00:00
parent 6091208331
commit 2b21a7cf36
7 changed files with 184 additions and 9 deletions
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11
llvm/lib/Analysis/ValueTracking.cpp
View File

@ -3394,8 +3394,15 @@ static Constant *lookThroughCast(ICmpInst *CmpI, Value *V1, Value *V2,
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))

9
llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@ -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<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))

13
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -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<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))

24
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -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<Instruction>(LHS),SPF2,LHS2,RHS2,
SI, SPF, RHS))

7
llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
View File

@ -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,

17
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -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<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);
@ -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).

112
llvm/test/Transforms/InstCombine/minmax-fold.ll Normal file
View File

@ -0,0 +1,112 @@
; 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
}