[CGP] Fix the rematerialization of gc.relocates

If we want to substitute the relocation of derived pointer with gep of base then
we must ensure that relocation of base dominates the relocation of derived pointer.

Currently only check for basic block is present. However it is possible that both
relocation are in the same basic block but relocation of derived pointer is defined
earlier.

The patch moves the relocation of base pointer right before relocation of derived
pointer in this case.

Reviewers: sanjoy,artagnon,igor-laevsky,reames
Reviewed By: reames
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D36462

llvm-svn: 311067

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index df900d65cf2..6d0043ba9e0 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -948,6 +948,21 @@ static bool
 simplifyRelocatesOffABase(GCRelocateInst *RelocatedBase,
                           const SmallVectorImpl<GCRelocateInst *> &Targets) {
   bool MadeChange = false;
+  // We must ensure the relocation of derived pointer is defined after
+  // relocation of base pointer. If we find a relocation corresponding to base
+  // defined earlier than relocation of base then we move relocation of base
+  // right before found relocation. We consider only relocation in the same
+  // basic block as relocation of base. Relocations from other basic block will
+  // be skipped by optimization and we do not care about them.
+  for (auto R = RelocatedBase->getParent()->getFirstInsertionPt();
+       &*R != RelocatedBase; ++R)
+    if (auto RI = dyn_cast<GCRelocateInst>(R))
+      if (RI->getStatepoint() == RelocatedBase->getStatepoint())
+        if (RI->getBasePtrIndex() == RelocatedBase->getBasePtrIndex()) {
+          RelocatedBase->moveBefore(RI);
+          break;
+        }
+
   for (GCRelocateInst *ToReplace : Targets) {
     assert(ToReplace->getBasePtrIndex() == RelocatedBase->getBasePtrIndex() &&
            "Not relocating a derived object of the original base object");