Make RecursivelyDeleteDeadPHINode delete a phi node that has no users and add a

test for that. With this change, test/CodeGen/X86/codegen-dce.ll no longer finds
any instructions to DCE, so delete the test.

Also renamed J and JP to I and IP in RecursivelyDeleteDeadPHINode.

llvm-svn: 126088

llvm/lib/Transforms/Utils/Local.cpp

@@ -283,6 +283,11 @@ static bool areAllUsesEqual(Instruction *I) {
 /// delete it.  If that makes any of its operands trivially dead, delete them
 /// too, recursively.  Return true if the PHI node is actually deleted.
 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
+  if (PN->use_empty()) {
+    PN->eraseFromParent();
+    return true;
+  }
+
   // We can remove a PHI if it is on a cycle in the def-use graph
   // where each node in the cycle has degree one, i.e. only one use,
   // and is an instruction with no side effects.
@@ -292,16 +297,16 @@ bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
   bool Changed = false;
   SmallPtrSet<PHINode *, 4> PHIs;
   PHIs.insert(PN);
-  for (Instruction *J = cast<Instruction>(*PN->use_begin());
-       areAllUsesEqual(J) && !J->mayHaveSideEffects();
-       J = cast<Instruction>(*J->use_begin()))
+  for (Instruction *I = cast<Instruction>(*PN->use_begin());
+       areAllUsesEqual(I) && !I->mayHaveSideEffects();
+       I = cast<Instruction>(*I->use_begin()))
     // If we find a PHI more than once, we're on a cycle that
     // won't prove fruitful.
-    if (PHINode *JP = dyn_cast<PHINode>(J))
-      if (!PHIs.insert(JP)) {
+    if (PHINode *IP = dyn_cast<PHINode>(I))
+      if (!PHIs.insert(IP)) {
         // Break the cycle and delete the PHI and its operands.
-        JP->replaceAllUsesWith(UndefValue::get(JP->getType()));
-        (void)RecursivelyDeleteTriviallyDeadInstructions(JP);
+        IP->replaceAllUsesWith(UndefValue::get(IP->getType()));
+        (void)RecursivelyDeleteTriviallyDeadInstructions(IP);
         Changed = true;
         break;
       }

llvm/test/CodeGen/X86/codegen-dce.ll

@@ -1,43 +0,0 @@
-; RUN: llc < %s -march=x86 -stats |& grep {codegen-dce} | grep {Number of dead instructions deleted}
-
-	%struct.anon = type { [3 x double], double, %struct.node*, [64 x %struct.bnode*], [64 x %struct.bnode*] }
-	%struct.bnode = type { i16, double, [3 x double], i32, i32, [3 x double], [3 x double], [3 x double], double, %struct.bnode*, %struct.bnode* }
-	%struct.node = type { i16, double, [3 x double], i32, i32 }
-
-define i32 @main(i32 %argc, i8** nocapture %argv) nounwind {
-entry:
-	%0 = malloc %struct.anon		; <%struct.anon*> [#uses=2]
-	%1 = getelementptr %struct.anon* %0, i32 0, i32 2		; <%struct.node**> [#uses=1]
-	br label %bb14.i
-
-bb14.i:		; preds = %bb14.i, %entry
-	%i8.0.reg2mem.0.i = phi i32 [ 0, %entry ], [ %2, %bb14.i ]		; <i32> [#uses=1]
-	%2 = add i32 %i8.0.reg2mem.0.i, 1		; <i32> [#uses=2]
-	%exitcond74.i = icmp eq i32 %2, 32		; <i1> [#uses=1]
-	br i1 %exitcond74.i, label %bb32.i, label %bb14.i
-
-bb32.i:		; preds = %bb32.i, %bb14.i
-	%tmp.0.reg2mem.0.i = phi i32 [ %indvar.next63.i, %bb32.i ], [ 0, %bb14.i ]		; <i32> [#uses=1]
-	%indvar.next63.i = add i32 %tmp.0.reg2mem.0.i, 1		; <i32> [#uses=2]
-	%exitcond64.i = icmp eq i32 %indvar.next63.i, 64		; <i1> [#uses=1]
-	br i1 %exitcond64.i, label %bb47.loopexit.i, label %bb32.i
-
-bb.i.i:		; preds = %bb47.loopexit.i
-	unreachable
-
-stepsystem.exit.i:		; preds = %bb47.loopexit.i
-	store %struct.node* null, %struct.node** %1, align 4
-	br label %bb.i6.i
-
-bb.i6.i:		; preds = %bb.i6.i, %stepsystem.exit.i
-	br i1 false, label %bb107.i.i, label %bb.i6.i
-
-bb107.i.i:		; preds = %bb107.i.i, %bb.i6.i
-	%q_addr.0.i.i.in = phi %struct.bnode** [ null, %bb107.i.i ], [ %3, %bb.i6.i ]		; <%struct.bnode**> [#uses=0]
-	br label %bb107.i.i
-
-bb47.loopexit.i:		; preds = %bb32.i
-	%3 = getelementptr %struct.anon* %0, i32 0, i32 4, i32 0		; <%struct.bnode**> [#uses=1]
-	%4 = icmp eq %struct.node* null, null		; <i1> [#uses=1]
-	br i1 %4, label %stepsystem.exit.i, label %bb.i.i
-}

llvm/unittests/Transforms/Utils/Local.cpp

@@ -42,6 +42,11 @@ TEST(Local, RecursivelyDeleteDeadPHINodes) {
   EXPECT_EQ(&bb0->front(), br0);
   EXPECT_EQ(&bb1->front(), br1);
 
+  builder.SetInsertPoint(bb0);
+  phi = builder.CreatePHI(Type::getInt32Ty(C));
+
+  EXPECT_TRUE(RecursivelyDeleteDeadPHINode(phi));
+
   bb0->dropAllReferences();
   bb1->dropAllReferences();
   delete bb0;