1 files changed, 10 insertions, 5 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 71a5ae24eead..3f064cfda712 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -1219,7 +1219,7 @@ Value *InstCombinerImpl::SimplifyDemandedVectorElts(Value *V,
       for (auto I = gep_type_begin(GEP), E = gep_type_end(GEP);
            I != E; I++)
         if (I.isStruct())
-          return true;;
+          return true;
       return false;
     };
     if (mayIndexStructType(cast<GetElementPtrInst>(*I)))
@@ -1228,10 +1228,11 @@ Value *InstCombinerImpl::SimplifyDemandedVectorElts(Value *V,
     // 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
-    // merge the undef bits here since gepping with either an undef base or
-    // index results in undef.
+    // merge the undef bits here since gepping with either an poison base or
+    // index results in poison.
     for (unsigned i = 0; i < I->getNumOperands(); i++) {
-      if (match(I->getOperand(i), m_Undef())) {
+      if (i == 0 ? match(I->getOperand(i), m_Undef())
+                 : match(I->getOperand(i), m_Poison())) {
         // If the entire vector is undefined, just return this info.
         UndefElts = EltMask;
         return nullptr;
@@ -1239,7 +1240,11 @@ Value *InstCombinerImpl::SimplifyDemandedVectorElts(Value *V,
       if (I->getOperand(i)->getType()->isVectorTy()) {
         APInt UndefEltsOp(VWidth, 0);
         simplifyAndSetOp(I, i, DemandedElts, UndefEltsOp);
-        UndefElts |= UndefEltsOp;
+        // gep(x, undef) is not undef, so skip considering idx ops here
+        // Note that we could propagate poison, but we can't distinguish between
+        // undef & poison bits ATM
+        if (i == 0)
+          UndefElts |= UndefEltsOp;
       }
     }