[llvm] 07ecdd9 - [IR][PatternMatch] `m_Not`: do not apply inner matcher unless `Not` matched

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2022-12-17T05:18:54+03:00
New Revision: 07ecdd9b1a8af51f07d5f4dfe46845c801482a39

URL: https://github.com/llvm/llvm-project/commit/07ecdd9b1a8af51f07d5f4dfe46845c801482a39
DIFF: https://github.com/llvm/llvm-project/commit/07ecdd9b1a8af51f07d5f4dfe46845c801482a39.diff

LOG: [IR][PatternMatch] `m_Not`: do not apply inner matcher unless `Not` matched

This is consistent with how other commutative matchers operate,
and i assumed that is how this one worked, alas it did not,
and thus `foldNestedSelects()` was miscompiling stuff.

Added: 
    

Modified: 
    llvm/include/llvm/IR/PatternMatch.h
    llvm/test/Transforms/InstCombine/D139275_c4001580.ll
    llvm/unittests/IR/PatternMatch.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/IR/PatternMatch.h b/llvm/include/llvm/IR/PatternMatch.h
index efb50a6b58c2..9dc8cf90fd98 100644
--- a/llvm/include/llvm/IR/PatternMatch.h
+++ b/llvm/include/llvm/IR/PatternMatch.h
@@ -2295,10 +2295,12 @@ m_NSWNeg(const ValTy &V) {
 }
 
 /// Matches a 'Not' as 'xor V, -1' or 'xor -1, V'.
+/// NOTE: we first match the 'Not' (by matching '-1'),
+/// and only then match the inner matcher!
 template <typename ValTy>
-inline BinaryOp_match<ValTy, cst_pred_ty<is_all_ones>, Instruction::Xor, true>
+inline BinaryOp_match<cst_pred_ty<is_all_ones>, ValTy, Instruction::Xor, true>
 m_Not(const ValTy &V) {
-  return m_c_Xor(V, m_AllOnes());
+  return m_c_Xor(m_AllOnes(), V);
 }
 
 template <typename ValTy> struct NotForbidUndef_match {

diff  --git a/llvm/test/Transforms/InstCombine/D139275_c4001580.ll b/llvm/test/Transforms/InstCombine/D139275_c4001580.ll
index 378d87153a16..9eb2e9138584 100644
--- a/llvm/test/Transforms/InstCombine/D139275_c4001580.ll
+++ b/llvm/test/Transforms/InstCombine/D139275_c4001580.ll
@@ -5,8 +5,10 @@
 ; FIXME: this is a miscompile.
 define i8 @D139275_c4001580(i1 %c0, i1 %c1, i1 %c2, i8 %inner.sel.trueval, i8 %inner.sel.falseval, i8 %outer.sel.trueval) {
 ; CHECK-LABEL: @D139275_c4001580(
-; CHECK-NEXT:    [[INNER_SEL:%.*]] = select i1 [[C2:%.*]], i8 [[OUTER_SEL_TRUEVAL:%.*]], i8 [[INNER_SEL_TRUEVAL:%.*]]
-; CHECK-NEXT:    [[OUTER_SEL:%.*]] = select i1 [[C1:%.*]], i8 [[INNER_SEL]], i8 [[INNER_SEL_FALSEVAL:%.*]]
+; CHECK-NEXT:    [[INNER_COND:%.*]] = xor i1 [[C0:%.*]], [[C1:%.*]]
+; CHECK-NEXT:    [[OUTER_COND:%.*]] = and i1 [[C2:%.*]], [[C1]]
+; CHECK-NEXT:    [[INNER_SEL:%.*]] = select i1 [[INNER_COND]], i8 [[INNER_SEL_TRUEVAL:%.*]], i8 [[INNER_SEL_FALSEVAL:%.*]]
+; CHECK-NEXT:    [[OUTER_SEL:%.*]] = select i1 [[OUTER_COND]], i8 [[OUTER_SEL_TRUEVAL:%.*]], i8 [[INNER_SEL]]
 ; CHECK-NEXT:    ret i8 [[OUTER_SEL]]
 ;
   %inner.cond = xor i1 %c0, %c1

diff  --git a/llvm/unittests/IR/PatternMatch.cpp b/llvm/unittests/IR/PatternMatch.cpp
index ab35df016cdd..6c0395131eb9 100644
--- a/llvm/unittests/IR/PatternMatch.cpp
+++ b/llvm/unittests/IR/PatternMatch.cpp
@@ -550,6 +550,20 @@ TEST_F(PatternMatchTest, Power2) {
   EXPECT_TRUE(m_NegatedPower2().match(CNegIntMin));
 }
 
+TEST_F(PatternMatchTest, Not) {
+  Value *C1 = IRB.getInt32(1);
+  Value *C2 = IRB.getInt32(2);
+  Value *C3 = IRB.getInt32(3);
+  Instruction *Not = BinaryOperator::CreateXor(C1, C2);
+
+  // When `m_Not` does not match the `not` itself,
+  // it should not try to apply the inner matcher.
+  Value *Val = C3;
+  EXPECT_FALSE(m_Not(m_Value(Val)).match(Not));
+  EXPECT_EQ(Val, C3);
+  Not->deleteValue();
+}
+
 TEST_F(PatternMatchTest, CommutativeDeferredValue) {
   Value *X = IRB.getInt32(1);
   Value *Y = IRB.getInt32(2);