[Local] Promote an utility that could be used elsewhere. NFCI.

llvm-svn: 348804

llvm/include/llvm/Transforms/Utils/Local.h

@@ -174,6 +174,12 @@ bool RecursivelyDeleteDeadPHINode(PHINode *PN,
 bool SimplifyInstructionsInBlock(BasicBlock *BB,
                                  const TargetLibraryInfo *TLI = nullptr);
 
+/// Replace all the uses of an SSA value in @llvm.dbg intrinsics with
+/// undef. This is useful for signaling that a variable, e.g. has been
+/// found dead and hence it's unavailable at a given program point.
+/// Returns true if the dbg values have been changed.
+bool replaceDbgUsesWithUndef(Instruction *I);
+
 //===----------------------------------------------------------------------===//
 //  Control Flow Graph Restructuring.
 //

llvm/lib/Transforms/Scalar/Reassociate.cpp

@@ -789,13 +789,7 @@ void ReassociatePass::RewriteExprTree(BinaryOperator *I,
       // Discard any debug info related to the expressions that has changed (we
       // can leave debug infor related to the root, since the result of the
       // expression tree should be the same even after reassociation).
-      SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
-      findDbgUsers(DbgUsers, ExpressionChanged);
-      for (auto *DII : DbgUsers) {
-        Value *Undef = UndefValue::get(ExpressionChanged->getType());
-        DII->setOperand(0, MetadataAsValue::get(DII->getContext(),
-                                                ValueAsMetadata::get(Undef)));
-      }
+      replaceDbgUsesWithUndef(ExpressionChanged);
 
       ExpressionChanged->moveBefore(I);
       ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->user_begin());

llvm/lib/Transforms/Utils/Local.cpp

@@ -476,6 +476,17 @@ void llvm::RecursivelyDeleteTriviallyDeadInstructions(
   }
 }
 
+bool llvm::replaceDbgUsesWithUndef(Instruction *I) {
+  SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
+  findDbgUsers(DbgUsers, I);
+  for (auto *DII : DbgUsers) {
+    Value *Undef = UndefValue::get(I->getType());
+    DII->setOperand(0, MetadataAsValue::get(DII->getContext(),
+                                            ValueAsMetadata::get(Undef)));
+  }
+  return !DbgUsers.empty();
+}
+
 /// areAllUsesEqual - Check whether the uses of a value are all the same.
 /// This is similar to Instruction::hasOneUse() except this will also return
 /// true when there are no uses or multiple uses that all refer to the same