[RS4GC] Look through vector bitcasts when looking for base pointer

Summary:
 In RS4GC it is possible that a base pointer is contained in a vector that
has undergone a bitcast from one element-pointertype to another. We teach
RS4GC how to look through bitcasts of vector types when looking for a base
pointer.

Reviewers: anna

Reviewed By: anna

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D38849

llvm-svn: 315694

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp b/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
index 4b8ddb7cc24..1ca77cfec32 100644
--- a/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
+++ b/llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
@@ -421,6 +421,11 @@ findBaseDefiningValueOfVector(Value *I) {
   if (auto *GEP = dyn_cast<GetElementPtrInst>(I))
     return findBaseDefiningValue(GEP->getPointerOperand());
 
+  // If the pointer comes through a bitcast of a vector of pointers to
+  // a vector of another type of pointer, then look through the bitcast
+  if (auto *BC = dyn_cast<BitCastInst>(I))
+    return findBaseDefiningValue(BC->getOperand(0));
+
   // A PHI or Select is a base defining value.  The outer findBasePointer
   // algorithm is responsible for constructing a base value for this BDV.
   assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&