[PATCH] D48535: [InstCombine] (A + 1) + (B ^ -1) --> A - B

[Gil Rapaport via Phabricator via llvm-commits]

gilr updated this revision to Diff 152684.
gilr added a comment.

Impl. Sanjay comments.
Thanks for taking the time guys!


https://reviews.llvm.org/D48535

Files:
  lib/Transforms/InstCombine/InstCombineAddSub.cpp
  test/Transforms/InstCombine/add.ll


Index: test/Transforms/InstCombine/add.ll
===================================================================
--- test/Transforms/InstCombine/add.ll
+++ test/Transforms/InstCombine/add.ll
@@ -780,3 +780,40 @@
   %value = add <2 x i32> <i32 123, i32 333>, %A
   ret <2 x i32> %value
 }
+
+; E = (A + 1) + ~B = A - B
+define i32 @add_not_increment(i32 %A, i32 %B) {
+; CHECK-LABEL: @add_not_increment(
+; CHECK-NEXT:    [[E:%.*]] = sub i32 %A, %B
+; CHECK-NEXT:    ret i32 [[E]]
+;
+  %C = xor i32 %B, -1
+  %D = add i32 %A, 1
+  %E = add i32 %D, %C
+  ret i32 %E
+}
+
+; E = (A + 1) + ~B = A - B
+define <2 x i32> @add_not_increment_vec(<2 x i32> %A, <2 x i32> %B) {
+; CHECK-LABEL: @add_not_increment_vec(
+; CHECK-NEXT:    [[E:%.*]] = sub <2 x i32> %A, %B
+; CHECK-NEXT:    ret <2 x i32> [[E]]
+;
+  %C = xor <2 x i32> %B, <i32 -1, i32 -1>
+  %D = add <2 x i32> %A, <i32 1, i32 1>
+  %E = add <2 x i32> %D, %C
+  ret <2 x i32> %E
+}
+
+; E = ~B + (1 + A) = A - B
+define i32 @add_not_increment_commuted(i32 %A, i32 %B) {
+; CHECK-LABEL: @add_not_increment_commuted(
+; CHECK-NEXT:    [[E:%.*]] = sub i32 %A, %B
+; CHECK-NEXT:    ret i32 [[E]]
+;
+  %C = xor i32 %B, -1
+  %D = add i32 %A, 1
+  %E = add i32 %C, %D
+  ret i32 %E
+}
+
Index: lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1212,6 +1212,11 @@
   if (Value *V = checkForNegativeOperand(I, Builder))
     return replaceInstUsesWith(I, V);
 
+  // (A + 1) + ~B --> A - B
+  // ~B + (A + 1) --> A - B
+  if (match(&I, m_c_BinOp(m_Add(m_Value(A), m_One()), m_Not(m_Value(B)))))
+    return BinaryOperator::CreateSub(A, B);
+
   // X % C0 + (( X / C0 ) % C1) * C0 => X % (C0 * C1)
   if (Value *V = SimplifyAddWithRemainder(I)) return replaceInstUsesWith(I, V);
 


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