From b789165e6bd13757da0243618757211d9530e078 Mon Sep 17 00:00:00 2001
From: Florian Hahn <florian.hahn@arm.com>
Date: Thu, 19 Apr 2018 15:05:47 +0000
Subject: [NewGVN] Add ops as dependency if we cannot find a leader for
 ValueOp.

If those operands change, we might find a leader for ValueOp, which
could enable new phi-of-op creation.

This fixes a case where we missed creating a phi-of-ops node. With D43865
and this patch, bootstrapping clang/llvm works with -enable-newgvn, whereas
without it, the "value changed after iteration" assertion is triggered.

Reviewers: dberlin, davide

Reviewed By: dberlin

Differential Revision: https://reviews.llvm.org/D42180

llvm-svn: 330334
---
 llvm/lib/Transforms/Scalar/NewGVN.cpp | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

(limited to 'llvm/lib/Transforms')

diff --git a/llvm/lib/Transforms/Scalar/NewGVN.cpp b/llvm/lib/Transforms/Scalar/NewGVN.cpp
index e82f69a8aa9..3de8d170bcd 100644
--- a/llvm/lib/Transforms/Scalar/NewGVN.cpp
+++ b/llvm/lib/Transforms/Scalar/NewGVN.cpp
@@ -2753,6 +2753,7 @@ NewGVN::makePossiblePHIOfOps(Instruction *I,
         // Clone the instruction, create an expression from it that is
         // translated back into the predecessor, and see if we have a leader.
         Instruction *ValueOp = I->clone();
+        SmallPtrSet<Value *, 4> CurrentDeps;
         if (MemAccess)
           TempToMemory.insert({ValueOp, MemAccess});
         bool SafeForPHIOfOps = true;
@@ -2764,7 +2765,7 @@ NewGVN::makePossiblePHIOfOps(Instruction *I,
           if (isa<PHINode>(Op)) {
             Op = Op->DoPHITranslation(PHIBlock, PredBB);
             if (Op != OrigOp && Op != I)
-              Deps.insert(Op);
+              CurrentDeps.insert(Op);
           } else if (auto *ValuePHI = RealToTemp.lookup(Op)) {
             if (getBlockForValue(ValuePHI) == PHIBlock)
               Op = ValuePHI->getIncomingValueForBlock(PredBB);
@@ -2783,8 +2784,16 @@ NewGVN::makePossiblePHIOfOps(Instruction *I,
                                     : findLeaderForInst(ValueOp, Visited,
                                                         MemAccess, I, PredBB);
         ValueOp->deleteValue();
-        if (!FoundVal)
+        if (!FoundVal) {
+          // We failed to find a leader for the current ValueOp, but this might
+          // change in case of the translated operands change.
+          if (SafeForPHIOfOps)
+            for (auto Dep : CurrentDeps)
+              addAdditionalUsers(Dep, I);
+
           return nullptr;
+        }
+        Deps.insert(CurrentDeps.begin(), CurrentDeps.end());
       } else {
         DEBUG(dbgs() << "Skipping phi of ops operand for incoming block "
                      << getBlockName(PredBB)
-- 
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