[NewGVN] Update phi-of-ops def block when updating existing ValuePHI.

In case we update a ValuePHI node created earlier, we could update it
based on a different OpPHI which could be in a different block.
We need to update the TempToBlock mapping reflecting the new block,
otherwise we would end up placing the new phi node in a wrong block.

This problem is exposed by the test case in
https://bugs.llvm.org/show_bug.cgi?id=36504.

This patch fixes a slightly simpler problem than in the bug report. In
the bug's re-producer, the additional problem is that we are re-using a
ValuePHI node with to few incoming values for the new OpPHI. If this
patch makes sense, I will follow it up with a patch that creates a new
PHI node if the existing PHI node has a different number of incoming
values.

Reviewers: davide, dberlin

Reviewed By: dberlin

Differential Revision: https://reviews.llvm.org/D43770

llvm-svn: 326181

1 files changed, 1 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/NewGVN.cpp b/llvm/lib/Transforms/Scalar/NewGVN.cpp
index 5e6b58055ec..2a58d0b4383 100644
--- a/llvm/lib/Transforms/Scalar/NewGVN.cpp
+++ b/llvm/lib/Transforms/Scalar/NewGVN.cpp
@@ -2819,6 +2819,7 @@ NewGVN::makePossiblePHIOfOps(Instruction *I,
       for (auto PHIOp : Ops)
         ValuePHI->addIncoming(PHIOp.first, PHIOp.second);
     } else {
+      TempToBlock[ValuePHI] = PHIBlock;
       unsigned int i = 0;
       for (auto PHIOp : Ops) {
         ValuePHI->setIncomingValue(i, PHIOp.first);