[llvm] r237453 - Canonicalize min/max expressions correctly.
James Molloy
james at jamesmolloy.co.uk
Fri May 15 09:50:51 PDT 2015
Hi Alexey,
My commit appears to have caused a failure in your bot:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-autoconf/builds/3827
but the stdio makes it seem like the process got killed (out of memory?)
Could you please let me know if it was indeed my patch or if it's a glitch
in your bot? And if so how I could reproduce (or more ideally the .cpp/.sh
files in /tmp)?
Cheers,
James
On Fri, 15 May 2015 at 17:17 James Molloy <james.molloy at arm.com> wrote:
> Author: jamesm
> Date: Fri May 15 11:10:59 2015
> New Revision: 237453
>
> URL: http://llvm.org/viewvc/llvm-project?rev=237453&view=rev
> Log:
> 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.
>
> Added:
> llvm/trunk/test/Transforms/InstCombine/minmax-fold.ll
> Modified:
> llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
> llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
> llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
>
> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=237453&r1=237452&r2=237453&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
> (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Fri May
> 15 11:10:59 2015
> @@ -3970,6 +3970,19 @@ Instruction *InstCombiner::visitFCmpInst
> }
> }
>
> + // 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))
>
> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp?rev=237453&r1=237452&r2=237453&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp Fri May 15
> 11:10:59 2015
> @@ -1154,18 +1154,30 @@ Instruction *InstCombiner::visitSelectIn
> }
>
> // 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))
>
> Modified: llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp?rev=237453&r1=237452&r2=237453&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp
> (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstructionCombining.cpp Fri May
> 15 11:10:59 2015
> @@ -714,6 +714,22 @@ Instruction *InstCombiner::FoldOpIntoSel
> 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::FoldOpIntoSel
> 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).
>
> Added: llvm/trunk/test/Transforms/InstCombine/minmax-fold.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/minmax-fold.ll?rev=237453&view=auto
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/minmax-fold.ll (added)
> +++ llvm/trunk/test/Transforms/InstCombine/minmax-fold.ll Fri May 15
> 11:10:59 2015
> @@ -0,0 +1,73 @@
> +; 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
> +}
>
>
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