[PATCH] D50301: [InstCombine] De Morgan: sink 'not' into 'xor' (PR38446)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri updated this revision to Diff 159652.
lebedev.ri marked 4 inline comments as done.
lebedev.ri added a comment.

Limit transform to only the free-to-invert cases.


Repository:
  rL LLVM

https://reviews.llvm.org/D50301

Files:
  lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  test/Transforms/InstCombine/demorgan-sink-not-into-xor.ll


Index: test/Transforms/InstCombine/demorgan-sink-not-into-xor.ll
===================================================================
--- test/Transforms/InstCombine/demorgan-sink-not-into-xor.ll
+++ test/Transforms/InstCombine/demorgan-sink-not-into-xor.ll
@@ -23,9 +23,8 @@
 define i1 @positive_easyinvert(i16 %x, i8 %y) {
 ; CHECK-LABEL: @positive_easyinvert(
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt i16 [[X:%.*]], 0
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp slt i8 [[Y:%.*]], 0
-; CHECK-NEXT:    [[TMP3:%.*]] = xor i1 [[TMP2]], [[TMP1]]
-; CHECK-NEXT:    [[TMP4:%.*]] = xor i1 [[TMP3]], true
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp sgt i8 [[Y:%.*]], -1
+; CHECK-NEXT:    [[TMP4:%.*]] = xor i1 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i1 [[TMP4]]
 ;
   %tmp1 = icmp slt i16 %x, 0
@@ -38,9 +37,8 @@
 define i1 @positive_easyinvert0(i8 %y) {
 ; CHECK-LABEL: @positive_easyinvert0(
 ; CHECK-NEXT:    [[TMP1:%.*]] = call i1 @gen1()
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp slt i8 [[Y:%.*]], 0
-; CHECK-NEXT:    [[TMP3:%.*]] = xor i1 [[TMP2]], [[TMP1]]
-; CHECK-NEXT:    [[TMP4:%.*]] = xor i1 [[TMP3]], true
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp sgt i8 [[Y:%.*]], -1
+; CHECK-NEXT:    [[TMP4:%.*]] = xor i1 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i1 [[TMP4]]
 ;
   %tmp1 = call i1 @gen1()
@@ -53,9 +51,8 @@
 define i1 @positive_easyinvert1(i8 %y) {
 ; CHECK-LABEL: @positive_easyinvert1(
 ; CHECK-NEXT:    [[TMP1:%.*]] = call i1 @gen1()
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp slt i8 [[Y:%.*]], 0
-; CHECK-NEXT:    [[TMP3:%.*]] = xor i1 [[TMP1]], [[TMP2]]
-; CHECK-NEXT:    [[TMP4:%.*]] = xor i1 [[TMP3]], true
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp sgt i8 [[Y:%.*]], -1
+; CHECK-NEXT:    [[TMP4:%.*]] = xor i1 [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret i1 [[TMP4]]
 ;
   %tmp1 = call i1 @gen1()
Index: lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2452,6 +2452,30 @@
   return nullptr;
 }
 
+// Transform
+//   ~(x ^ y)
+// into:
+//   (~x) ^ y
+// or into
+//   x ^ (~y)
+static Instruction *sinkNotIntoXor(BinaryOperator &I,
+                                   InstCombiner::BuilderTy &Builder) {
+  Value *X, *Y;
+  if (!match(&I, m_Not(m_OneUse(m_Xor(m_Value(X), m_Value(Y))))))
+    return nullptr;
+
+  // We only want to do the transform if it is free to do.
+  if (IsFreeToInvert(X, X->hasOneUse())) {
+    // Ok, good.
+  } else if (IsFreeToInvert(Y, Y->hasOneUse())) {
+    std::swap(X, Y);
+  } else
+    return nullptr;
+
+  Value *NotX = Builder.CreateNot(X, X->getName() + ".not");
+  return BinaryOperator::CreateXor(NotX, Y, I.getName() + ".demorgan");
+}
+
 // FIXME: We use commutative matchers (m_c_*) for some, but not all, matches
 // here. We should standardize that construct where it is needed or choose some
 // other way to ensure that commutated variants of patterns are not missed.
@@ -2777,5 +2801,8 @@
     }
   }
 
+  if (Instruction *NewXor = sinkNotIntoXor(I, Builder))
+    return NewXor;
+
   return nullptr;
 }


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