[llvm] r324014 - [InstCombine] allow multi-use values in canEvaluate* if all uses are in 1 inst
Chandler Carruth via llvm-commits
llvm-commits at lists.llvm.org
Sat Feb 3 19:02:47 PST 2018
On Thu, Feb 1, 2018 at 1:57 PM Sanjay Patel via llvm-commits <
llvm-commits at lists.llvm.org> wrote:
> Author: spatel
> Date: Thu Feb 1 13:55:53 2018
> New Revision: 324014
>
> URL: http://llvm.org/viewvc/llvm-project?rev=324014&view=rev
> Log:
> [InstCombine] allow multi-use values in canEvaluate* if all uses are in 1
> inst
>
> This is the enhancement suggested in D42536 to fix a shortcoming in
> regular InstCombine's canEvaluate* functionality.
> When we have multiple uses of a value, but they're all in one instruction,
> we can
> allow that expression to be narrowed or widened for the same cost as a
> single-use
> value.
>
> AFAICT, this can only matter for multiply: sub/and/or/xor/select would be
> simplified
> away if the operands are the same value; add becomes shl; shifts with a
> variable shift
> amount aren't handled.
>
FWIW, we have at least one case which is now either inf-looping or taking
dramatically longer to compile after this commit (way over 2x from what I
can tell).
We're working on building a test case, but just wanted to send a heads-up
in case others are hitting slow compiles.
>
> Differential Revision: https://reviews.llvm.org/D42739
>
> Modified:
> llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
> llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll
> llvm/trunk/test/Transforms/InstCombine/icmp-mul-zext.ll
>
> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp?rev=324014&r1=324013&r2=324014&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Thu Feb 1
> 13:55:53 2018
> @@ -185,8 +185,14 @@ Value *InstCombiner::EvaluateInDifferent
> case Instruction::Shl:
> case Instruction::UDiv:
> case Instruction::URem: {
> - Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
> - Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
> + Value *LHS, *RHS;
> + if (I->getOperand(0) == I->getOperand(1)) {
> + // Don't create an unnecessary value if the operands are repeated.
> + LHS = RHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
> + } else {
> + LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
> + RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
> + }
> Res = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS);
> break;
> }
> @@ -320,10 +326,12 @@ static bool canNotEvaluateInType(Value *
> assert(!isa<Constant>(V) && "Constant should already be handled.");
> if (!isa<Instruction>(V))
> return true;
> - // We can't extend or shrink something that has multiple uses: doing so
> would
> - // require duplicating the instruction in general, which isn't
> profitable.
> + // We can't extend or shrink something that has multiple uses -- unless
> those
> + // multiple uses are all in the same instruction -- doing so would
> require
> + // duplicating the instruction which isn't profitable.
> if (!V->hasOneUse())
> - return true;
> + if (any_of(V->users(), [&](User *U) { return U != V->user_back(); }))
> + return true;
>
> return false;
> }
>
> Modified: llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll?rev=324014&r1=324013&r2=324014&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll Thu Feb 1
> 13:55:53 2018
> @@ -49,11 +49,9 @@ define i8 @select2(i1 %cond, i8 %x, i8 %
>
> define i32 @eval_trunc_multi_use_in_one_inst(i32 %x) {
> ; CHECK-LABEL: @eval_trunc_multi_use_in_one_inst(
> -; CHECK-NEXT: [[Z:%.*]] = zext i32 [[X:%.*]] to i64
> -; CHECK-NEXT: [[A:%.*]] = add nuw nsw i64 [[Z]], 15
> -; CHECK-NEXT: [[M:%.*]] = mul i64 [[A]], [[A]]
> -; CHECK-NEXT: [[T:%.*]] = trunc i64 [[M]] to i32
> -; CHECK-NEXT: ret i32 [[T]]
> +; CHECK-NEXT: [[A:%.*]] = add i32 [[X:%.*]], 15
> +; CHECK-NEXT: [[M:%.*]] = mul i32 [[A]], [[A]]
> +; CHECK-NEXT: ret i32 [[M]]
> ;
> %z = zext i32 %x to i64
> %a = add nsw nuw i64 %z, 15
> @@ -64,11 +62,9 @@ define i32 @eval_trunc_multi_use_in_one_
>
> define i32 @eval_zext_multi_use_in_one_inst(i32 %x) {
> ; CHECK-LABEL: @eval_zext_multi_use_in_one_inst(
> -; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i16
> -; CHECK-NEXT: [[A:%.*]] = and i16 [[T]], 5
> -; CHECK-NEXT: [[M:%.*]] = mul nuw nsw i16 [[A]], [[A]]
> -; CHECK-NEXT: [[R:%.*]] = zext i16 [[M]] to i32
> -; CHECK-NEXT: ret i32 [[R]]
> +; CHECK-NEXT: [[A:%.*]] = and i32 [[X:%.*]], 5
> +; CHECK-NEXT: [[M:%.*]] = mul nuw nsw i32 [[A]], [[A]]
> +; CHECK-NEXT: ret i32 [[M]]
> ;
> %t = trunc i32 %x to i16
> %a = and i16 %t, 5
> @@ -79,12 +75,10 @@ define i32 @eval_zext_multi_use_in_one_i
>
> define i32 @eval_sext_multi_use_in_one_inst(i32 %x) {
> ; CHECK-LABEL: @eval_sext_multi_use_in_one_inst(
> -; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i16
> -; CHECK-NEXT: [[A:%.*]] = and i16 [[T]], 14
> -; CHECK-NEXT: [[M:%.*]] = mul nuw nsw i16 [[A]], [[A]]
> -; CHECK-NEXT: [[O:%.*]] = or i16 [[M]], -32768
> -; CHECK-NEXT: [[R:%.*]] = sext i16 [[O]] to i32
> -; CHECK-NEXT: ret i32 [[R]]
> +; CHECK-NEXT: [[A:%.*]] = and i32 [[X:%.*]], 14
> +; CHECK-NEXT: [[M:%.*]] = mul nuw nsw i32 [[A]], [[A]]
> +; CHECK-NEXT: [[O:%.*]] = or i32 [[M]], -32768
> +; CHECK-NEXT: ret i32 [[O]]
> ;
> %t = trunc i32 %x to i16
> %a = and i16 %t, 14
>
> Modified: llvm/trunk/test/Transforms/InstCombine/icmp-mul-zext.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp-mul-zext.ll?rev=324014&r1=324013&r2=324014&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/icmp-mul-zext.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/icmp-mul-zext.ll Thu Feb 1
> 13:55:53 2018
> @@ -55,13 +55,12 @@ lor.end:
>
> define void @PR33765(i8 %beth) {
> ; CHECK-LABEL: @PR33765(
> -; CHECK-NEXT: [[CONV:%.*]] = zext i8 [[BETH:%.*]] to i32
> +; CHECK-NEXT: [[CONV:%.*]] = zext i8 [[BETH:%.*]] to i16
> ; CHECK-NEXT: br i1 false, label [[IF_THEN9:%.*]], label [[IF_THEN9]]
> ; CHECK: if.then9:
> -; CHECK-NEXT: [[MUL:%.*]] = mul nuw nsw i32 [[CONV]], [[CONV]]
> +; CHECK-NEXT: [[MUL:%.*]] = mul nuw i16 [[CONV]], [[CONV]]
> ; CHECK-NEXT: [[TINKY:%.*]] = load i16, i16* @glob, align 2
> -; CHECK-NEXT: [[TMP1:%.*]] = trunc i32 [[MUL]] to i16
> -; CHECK-NEXT: [[CONV14:%.*]] = and i16 [[TINKY]], [[TMP1]]
> +; CHECK-NEXT: [[CONV14:%.*]] = and i16 [[TINKY]], [[MUL]]
> ; CHECK-NEXT: store i16 [[CONV14]], i16* @glob, align 2
> ; CHECK-NEXT: ret void
> ;
>
>
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