Handle GEPs with all-zero indices in the same way we handle pointer-pointer bitcasts. Also, fix a potentia infinite loop.

This brings FastDSE to parity with old DSE on 175.vpr.

llvm-svn: 39839

1 files changed, 12 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/FastDSE.cpp b/llvm/lib/Transforms/Scalar/FastDSE.cpp
index 13e61366477..901a735e3c0 100644
--- a/llvm/lib/Transforms/Scalar/FastDSE.cpp
+++ b/llvm/lib/Transforms/Scalar/FastDSE.cpp
@@ -60,9 +60,18 @@ namespace {
       assert(isa<PointerType>(v->getType()) && "Translating a non-pointer type?");
       
       // See through pointer-to-pointer bitcasts
-      while (BitCastInst* C = dyn_cast<BitCastInst>(v))
-        if (isa<PointerType>(C->getSrcTy()))
-          v = C->getOperand(0);
+      while (isa<BitCastInst>(v) || isa<GetElementPtrInst>(v))
+        if (BitCastInst* C = dyn_cast<BitCastInst>(v)) {
+          if (isa<PointerType>(C->getSrcTy()))
+            v = C->getOperand(0);
+          else
+            break;
+        } else if (GetElementPtrInst* G = dyn_cast<GetElementPtrInst>(v)) {
+          if (G->hasAllZeroIndices())
+            v = G->getOperand(0);
+          else
+            break;
+        }
     }
 
     // getAnalysisUsage - We require post dominance frontiers (aka Control