[PATCH] D33226: [NewGVN] Replace predicate info leftovers

[Davide Italiano via Phabricator via llvm-commits]

davide created this revision.
Herald added a subscriber: Prazek.

For those watching, we were leaving some `ssa.copy` around and those arrived to the backend where we failed to lower.
The comment in the code contains the whole story, for those interested :)


https://reviews.llvm.org/D33226

Files:
  include/llvm/Transforms/Utils/PredicateInfo.h
  lib/Transforms/Scalar/NewGVN.cpp


Index: lib/Transforms/Scalar/NewGVN.cpp
===================================================================
--- lib/Transforms/Scalar/NewGVN.cpp
+++ lib/Transforms/Scalar/NewGVN.cpp
@@ -2779,6 +2779,29 @@

   Changed |= eliminateInstructions(F);

+  // Replace predicate info `ssa.copy` leftovers with their arguments, and
+  // mark for deletion.
+  // We replace a `ssa.copy` intrinsic in `eliminateInstructions` if the
+  // following two invariants hold:
+  // 1) The `ssa.copy` will be at least to its argument. We guarantee this
+  // by returning a variable consisting of the argument as the value number
+  // if we don't find anything using predicate info.
+  // 2) This will generate a congruence class that is either constant or has
+  // at least two members. In the latter case the argument should dominate
+  // all the uses and thus should be used to replace the operand.
+  // In some weird cases where the CFG is strange, 2) doesn't hold, so here
+  // we walk the map of predicate info finding instructions with at least one
+  // use.
+  auto &PredMap = PredInfo->getPredicateMap();
+  for (auto &P : PredMap) {
+    Value *Op = const_cast<Value *>(P.first);
+    auto *I = dyn_cast<Instruction>(Op);
+    if (I && !I->use_empty()) {
+      I->replaceAllUsesWith(I->getOperand(0));
+      markInstructionForDeletion(I);
+    }
+  }
+
   // Delete all instructions marked for deletion.
   for (Instruction *ToErase : InstructionsToErase) {
     if (!ToErase->use_empty())
Index: include/llvm/Transforms/Utils/PredicateInfo.h
===================================================================
--- include/llvm/Transforms/Utils/PredicateInfo.h
+++ include/llvm/Transforms/Utils/PredicateInfo.h
@@ -220,6 +220,10 @@
     return PredicateMap.lookup(V);
   }

+  DenseMap<const Value *, const PredicateBase *> &getPredicateMap() {
+    return PredicateMap;
+  }
+
 protected:
   // Used by PredicateInfo annotater, dumpers, and wrapper pass.
   friend class PredicateInfoAnnotatedWriter;


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