[llvm] r324014 - [InstCombine] allow multi-use values in canEvaluate* if all uses are in 1 inst
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Mon Feb 5 06:28:49 PST 2018
Thanks for letting me know. Sounds like an inf-loop.
Since this patch is duplicating a transform that occurs in
-aggressive-instcombine, it's possible that the bug already exists apart
from this change, but might take the benign form of a transform reversal
across passes, or it might be masked in that case.
On Sat, Feb 3, 2018 at 8:02 PM, Chandler Carruth <chandlerc at gmail.com>
wrote:
> 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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>
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