diff options
Diffstat (limited to 'lib/Transforms/InstCombine/InstCombineVectorOps.cpp')
| -rw-r--r-- | lib/Transforms/InstCombine/InstCombineVectorOps.cpp | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/lib/Transforms/InstCombine/InstCombineVectorOps.cpp index de8a3ac..5624305 100644 --- a/lib/Transforms/InstCombine/InstCombineVectorOps.cpp +++ b/lib/Transforms/InstCombine/InstCombineVectorOps.cpp @@ -614,11 +614,16 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) { // we are absolutely afraid of producing a shuffle mask not in the input // program, because the code gen may not be smart enough to turn a merged // shuffle into two specific shuffles: it may produce worse code. As such, - // we only merge two shuffles if the result is either a splat or one of the - // input shuffle masks. In this case, merging the shuffles just removes - // one instruction, which we know is safe. This is good for things like + // we only merge two shuffles if the result is a splat, one of the input + // input shuffle masks, or if there's only one input to the shuffle. + // In this case, merging the shuffles just removes one instruction, which + // we know is safe. This is good for things like // turning: (splat(splat)) -> splat, or // merge(V[0..n], V[n+1..2n]) -> V[0..2n] + // + // FIXME: This is almost certainly far, far too conservative. We should + // have a better model. Perhaps a TargetTransformInfo hook to ask whether + // a shuffle is considered OK? ShuffleVectorInst* LHSShuffle = dyn_cast<ShuffleVectorInst>(LHS); ShuffleVectorInst* RHSShuffle = dyn_cast<ShuffleVectorInst>(RHS); if (LHSShuffle) @@ -743,8 +748,10 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) { } // If the result mask is equal to one of the original shuffle masks, - // or is a splat, do the replacement. - if (isSplat || newMask == LHSMask || newMask == RHSMask || newMask == Mask) { + // or is a splat, do the replacement. Similarly, if there is only one + // input vector, go ahead and do the folding. + if (isSplat || newMask == LHSMask || newMask == RHSMask || newMask == Mask || + isa<UndefValue>(RHS)) { SmallVector<Constant*, 16> Elts; Type *Int32Ty = Type::getInt32Ty(SVI.getContext()); for (unsigned i = 0, e = newMask.size(); i != e; ++i) { |