[InstCombine] Limit a vector demanded elts rule which was producing invalid IR.

The demanded elts rules introduced for GEPs in https://reviews.llvm.org/rL356293 replaced vector constants with undefs (by design).  It turns out that the LangRef disallows such cases when indexing structs.  The right fix is probably to relax the langref requirement, and update other passes to expect the result, but for the moment, limit the transform to avoid compiler crashes.

This should fix https://bugs.llvm.org/show_bug.cgi?id=41624.

llvm-svn: 359633

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 1d52938d1f8..42406e27e35 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -1169,6 +1169,18 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
   default: break;
 
   case Instruction::GetElementPtr: {
+    // The LangRef requires that struct geps have all constant indices.  As
+    // such, we can't convert any operand to partial undef.
+    auto mayIndexStructType = [](GetElementPtrInst &GEP) {
+      for (auto I = gep_type_begin(GEP), E = gep_type_end(GEP);
+           I != E; I++)
+        if (I.isStruct())
+          return true;;
+      return false;
+    };
+    if (mayIndexStructType(cast<GetElementPtrInst>(*I)))
+      break;
+    
     // Conservatively track the demanded elements back through any vector
     // operands we may have.  We know there must be at least one, or we
     // wouldn't have a vector result to get here. Note that we intentionally