[PATCH] D51168: [NewGVN] Make sure we do not add a user to itself.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: davide, efriedma, mcrosier.
Herald added a subscriber: Prazek.

If we simplify an instruction to itself, we do not need to add a user to
itself. For congruence classes with a defining expression, we already
use a similar logic.

Fixes PR38259.


https://reviews.llvm.org/D51168

Files:
  lib/Transforms/Scalar/NewGVN.cpp
  test/Transforms/NewGVN/simp-to-self.ll


Index: test/Transforms/NewGVN/simp-to-self.ll
===================================================================
--- /dev/null
+++ test/Transforms/NewGVN/simp-to-self.ll
@@ -0,0 +1,27 @@
+; RUN: opt -S < %s -newgvn | FileCheck %s
+
+; CHECK-LABEL: for.cond:
+; CHECK-NEXT:    %lv = load i32, i32* bitcast (i64* @a to i32*)
+; CHECK-NEXT:    %bf.clear = and i32 %lv, -131072
+; CHECK-NEXT:    %bf.set = or i32 1, %bf.clear
+; CHECK-NEXT:    br i1 %bc, label %for.cond, label %exit
+ at a = external global i64
+
+define void @fn1(i1 %bc) {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond1.1, %entry
+  %tmp = phi i1 [ undef, %entry ], [ 1, %for.cond ]
+  %conv = zext i1 %tmp to i32
+  %lv = load i32, i32* bitcast (i64* @a to i32*)
+  %bf.clear = and i32 %lv, -131072
+  %bf.set = or i32 %conv, %bf.clear
+  %bf.clear.1 = and i32 %bf.set, -131072
+  %bf.set.1 = or i32 1, %bf.clear.1
+  br i1 %bc, label %for.cond, label %exit
+
+exit:                              ; preds = %for.cond1
+  store i32 %bf.set.1, i32* bitcast (i64* @a to i32*)
+  ret void
+}
Index: lib/Transforms/Scalar/NewGVN.cpp
===================================================================
--- lib/Transforms/Scalar/NewGVN.cpp
+++ lib/Transforms/Scalar/NewGVN.cpp
@@ -1087,9 +1087,13 @@
   CongruenceClass *CC = ValueToClass.lookup(V);
   if (CC) {
     if (CC->getLeader() && CC->getLeader() != I) {
-      // Don't add temporary instructions to the user lists.
-      if (!AllTempInstructions.count(I))
-        addAdditionalUsers(V, I);
+      // If we simplified to something else, we need to communicate
+      // that we're users of the value we simplified to.
+      if (I != V) {
+        // Don't add temporary instructions to the user lists.
+        if (!AllTempInstructions.count(I))
+          addAdditionalUsers(V, I);
+      }
       return createVariableOrConstant(CC->getLeader());
     }
     if (CC->getDefiningExpr()) {


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