[PATCH] D51922: [NewGVN] Apply SimplifySelectInst if any of the options is undef.

[Florian Hahn via Phabricator via llvm-commits]

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

The Simplify* functions expect undefs to be replaced as we go along, to
avoid the same undef use being used with different values.

See PR33165 for an extensive discussion of the issue.


https://reviews.llvm.org/D51922

Files:
  lib/Transforms/Scalar/NewGVN.cpp
  test/Transforms/NewGVN/pr33165.ll


Index: test/Transforms/NewGVN/pr33165.ll
===================================================================
--- /dev/null
+++ test/Transforms/NewGVN/pr33165.ll
@@ -0,0 +1,24 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -newgvn -S < %s | FileCheck %s
+
+define i2 @t1(i2, i1) {
+; CHECK-LABEL: @t1(
+; CHECK-NEXT:    [[A:%.*]] = xor i2 [[TMP0:%.*]], -1
+; CHECK-NEXT:    ret i2 [[A]]
+;
+  %a = xor i2 %0, -1
+  %b = select i1 %1, i2 %a, i2 undef
+  %c = and i2 %a, %b
+  ret i2 %c
+}
+
+define i2 @t2(i2, i1) {
+; CHECK-LABEL: @t2(
+; CHECK-NEXT:    [[A:%.*]] = xor i2 [[TMP0:%.*]], -1
+; CHECK-NEXT:    ret i2 [[A]]
+;
+  %a = xor i2 %0, -1
+  %b = select i1 %1, i2 undef, i2 %a
+  %c = and i2 %a, %b
+  ret i2 %c
+}
Index: lib/Transforms/Scalar/NewGVN.cpp
===================================================================
--- lib/Transforms/Scalar/NewGVN.cpp
+++ lib/Transforms/Scalar/NewGVN.cpp
@@ -1151,7 +1151,9 @@
       return SimplifiedE;
   } else if (isa<SelectInst>(I)) {
     if (isa<Constant>(E->getOperand(0)) ||
-        E->getOperand(1) == E->getOperand(2)) {
+        E->getOperand(1) == E->getOperand(2) ||
+        isa<UndefValue>(E->getOperand(1)) ||
+        isa<UndefValue>(E->getOperand(2))) {
       assert(E->getOperand(1)->getType() == I->getOperand(1)->getType() &&
              E->getOperand(2)->getType() == I->getOperand(2)->getType());
       Value *V = SimplifySelectInst(E->getOperand(0), E->getOperand(1),


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