[InstCombine][SSE] Add DemandedElts support for PSHUFB instructions

Simplify a pshufb shuffle mask based on the elements of the mask that are actually demanded.

Differential Revision: https://reviews.llvm.org/D28745

llvm-svn: 292101

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 8b930bd95df..95100d074b4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -1472,6 +1472,16 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
       break;
     }
 
+    case Intrinsic::x86_ssse3_pshuf_b_128:
+    case Intrinsic::x86_avx2_pshuf_b:
+    case Intrinsic::x86_avx512_pshuf_b_512: {
+      Value *Op1 = II->getArgOperand(1);
+      TmpV = SimplifyDemandedVectorElts(Op1, DemandedElts, UndefElts,
+                                        Depth + 1);
+      if (TmpV) { II->setArgOperand(1, TmpV); MadeChange = true; }
+      break;
+    }
+
     // SSE4A instructions leave the upper 64-bits of the 128-bit result
     // in an undefined state.
     case Intrinsic::x86_sse4a_extrq: