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[InstCombine] shrink truncated splat shuffle (2nd try) 

This was committed at r297155 and reverted at r297166 because of an
over-reaching clang test. That should be fixed with r297189.

This is one part of solving a recent bug report:
http://lists.llvm.org/pipermail/llvm-dev/2017-February/110293.html

This keeps with our general approach: changing arbitrary shuffles is off-limts,
but changing splat is ok. The transform is very similar to the existing
shrinkBitwiseLogic() canonicalization.

Differential Revision: https://reviews.llvm.org/D30123

llvm-svn: 297232
This commit is contained in:
Sanjay Patel 2017-03-07 21:45:16 +00:00
parent 7993cc5eed
commit 53fa17a014
2 changed files with 24 additions and 6 deletions
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20
llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@ -463,6 +463,23 @@ Instruction *InstCombiner::shrinkBitwiseLogic(TruncInst &Trunc) {
return BinaryOperator::Create(LogicOp->getOpcode(), NarrowOp0, NarrowC);
}
/// Try to narrow the width of a splat shuffle. This could be generalized to any
/// shuffle with a constant operand, but we limit the transform to avoid
/// creating a shuffle type that targets may not be able to lower effectively.
static Instruction *shrinkSplatShuffle(TruncInst &Trunc,
InstCombiner::BuilderTy &Builder) {
auto *Shuf = dyn_cast<ShuffleVectorInst>(Trunc.getOperand(0));
if (Shuf && Shuf->hasOneUse() && isa<UndefValue>(Shuf->getOperand(1)) &&
Shuf->getMask()->getSplatValue()) {
// trunc (shuf X, Undef, SplatMask) --> shuf (trunc X), Undef, SplatMask
Constant *NarrowUndef = UndefValue::get(Trunc.getType());
Value *NarrowOp = Builder.CreateTrunc(Shuf->getOperand(0), Trunc.getType());
return new ShuffleVectorInst(NarrowOp, NarrowUndef, Shuf->getMask());
}
return nullptr;
}
Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
if (Instruction *Result = commonCastTransforms(CI))
return Result;
@ -554,6 +571,9 @@ Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
if (Instruction *I = shrinkBitwiseLogic(CI))
return I;
if (Instruction *I = shrinkSplatShuffle(CI, *Builder))
return I;
if (Src->hasOneUse() && isa<IntegerType>(SrcTy) &&
shouldChangeType(SrcTy, DestTy)) {
// Transform "trunc (shl X, cst)" -> "shl (trunc X), cst" so long as the

10
llvm/test/Transforms/InstCombine/trunc.ll
View File

@ -478,13 +478,12 @@ define <4 x i8> @wide_shuf(<4 x i32> %x) {
ret <4 x i8> %trunc
}
; FIXME:
; trunc (shuffle X, undef, SplatMask) --> shuffle (trunc X), undef, SplatMask
define <4 x i8> @wide_splat1(<4 x i32> %x) {
; CHECK-LABEL: @wide_splat1(
; CHECK-NEXT: [[SHUF:%.*]] = shufflevector <4 x i32> %x, <4 x i32> undef, <4 x i32> <i32 2, i32 2, i32 2, i32 2>
; CHECK-NEXT: [[TRUNC:%.*]] = trunc <4 x i32> [[SHUF]] to <4 x i8>
; CHECK-NEXT: [[TMP1:%.*]] = trunc <4 x i32> %x to <4 x i8>
; CHECK-NEXT: [[TRUNC:%.*]] = shufflevector <4 x i8> [[TMP1]], <4 x i8> undef, <4 x i32> <i32 2, i32 2, i32 2, i32 2>
; CHECK-NEXT: ret <4 x i8> [[TRUNC]]
;
%shuf = shufflevector <4 x i32> %x, <4 x i32> undef, <4 x i32> <i32 2, i32 2, i32 2, i32 2>
@ -492,14 +491,13 @@ define <4 x i8> @wide_splat1(<4 x i32> %x) {
ret <4 x i8> %trunc
}
; FIXME:
; Test weird types.
; trunc (shuffle X, undef, SplatMask) --> shuffle (trunc X), undef, SplatMask
define <3 x i31> @wide_splat2(<3 x i33> %x) {
; CHECK-LABEL: @wide_splat2(
; CHECK-NEXT: [[SHUF:%.*]] = shufflevector <3 x i33> %x, <3 x i33> undef, <3 x i32> <i32 1, i32 1, i32 1>
; CHECK-NEXT: [[TRUNC:%.*]] = trunc <3 x i33> [[SHUF]] to <3 x i31>
; CHECK-NEXT: [[TMP1:%.*]] = trunc <3 x i33> %x to <3 x i31>
; CHECK-NEXT: [[TRUNC:%.*]] = shufflevector <3 x i31> [[TMP1]], <3 x i31> undef, <3 x i32> <i32 1, i32 1, i32 1>
; CHECK-NEXT: ret <3 x i31> [[TRUNC]]
;
%shuf = shufflevector <3 x i33> %x, <3 x i33> undef, <3 x i32> <i32 1, i32 1, i32 1>