[PATCH] D23920: [StatepointsForGC] Identify PHI values for rematerialization

[Anna Thomas via llvm-commits]

anna created this revision.
anna added reviewers: sanjoy, reames.
anna added a subscriber: llvm-commits.

While walking the use chain for identifying rematerializable values in RS4GC,
add the case where the current value and base value are the same PHI nodes.

This will aid rematerialization instead of adding gc.relocate.

https://reviews.llvm.org/D23920

Files:
  lib/Transforms/Scalar/RewriteStatepointsForGC.cpp

Index: lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
===================================================================
--- lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
+++ lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
@@ -1813,6 +1813,20 @@
                                                   CI->getOperand(0), BaseValue);
   }
 
+  // PHI nodes that have the same incoming values, and belonging to the same
+  // basic blocks are essentially the same SSA value.
+  if (PHINode *PhiCurr = dyn_cast<PHINode>(CurrentValue))
+    if (PHINode *PhiBase = dyn_cast<PHINode>(BaseValue)) {
+      int phiNum = PhiCurr->getNumIncomingValues();
+      if (phiNum != PhiBase->getNumIncomingValues() ||
+          PhiCurr->getParent() != PhiBase->getParent())
+        return false;
+      for (unsigned i = 0; i < phiNum; i++)
+        if (PhiCurr->getIncomingValue(i) != PhiBase->getIncomingValue(i))
+          return false;
+      return true;
+    }
+
   // Not supported instruction in the chain
   return false;
 }


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