[llvm] 5b78303 - [InstCombine] Fold `a & ~(a ^ b)` to `x & y`

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2020-12-24T21:20:49+03:00
New Revision: 5b78303433c0778a839e89d20daa57fbc037d0c7

URL: https://github.com/llvm/llvm-project/commit/5b78303433c0778a839e89d20daa57fbc037d0c7
DIFF: https://github.com/llvm/llvm-project/commit/5b78303433c0778a839e89d20daa57fbc037d0c7.diff

LOG: [InstCombine] Fold `a & ~(a ^ b)` to `x & y`

```
----------------------------------------
define i32 @and_xor_not_common_op(i32 %a, i32 %b) {
%0:
  %b2 = xor i32 %b, 4294967295
  %t2 = xor i32 %a, %b2
  %t4 = and i32 %t2, %a
  ret i32 %t4
}
=>
define i32 @and_xor_not_common_op(i32 %a, i32 %b) {
%0:
  %t4 = and i32 %a, %b
  ret i32 %t4
}
Transformation seems to be correct!
```

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
    llvm/test/Transforms/InstCombine/and-xor-or.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 6b5fd571ecf5..3c0cdaf6e843 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1883,6 +1883,13 @@ Instruction *InstCombinerImpl::visitAnd(BinaryOperator &I) {
     if (match(Op0, m_OneUse(m_c_Xor(m_Specific(Op1), m_Value(B)))))
       return BinaryOperator::CreateAnd(Op1, Builder.CreateNot(B));
 
+    // A & ~(A ^ B) --> A & B
+    if (match(Op1, m_Not(m_c_Xor(m_Specific(Op0), m_Value(B)))))
+      return BinaryOperator::CreateAnd(Op0, B);
+    // ~(A ^ B) & A --> A & B
+    if (match(Op0, m_Not(m_c_Xor(m_Specific(Op1), m_Value(B)))))
+      return BinaryOperator::CreateAnd(Op1, B);
+
     // (A ^ B) & ((B ^ C) ^ A) -> (A ^ B) & ~C
     if (match(Op0, m_Xor(m_Value(A), m_Value(B))))
       if (match(Op1, m_Xor(m_Xor(m_Specific(B), m_Value(C)), m_Specific(A))))

diff  --git a/llvm/test/Transforms/InstCombine/and-xor-or.ll b/llvm/test/Transforms/InstCombine/and-xor-or.ll
index 4a27e3f00c89..4cb88d0766ba 100644
--- a/llvm/test/Transforms/InstCombine/and-xor-or.ll
+++ b/llvm/test/Transforms/InstCombine/and-xor-or.ll
@@ -116,9 +116,7 @@ define i32 @and_xor_not_common_op_extrause(i32 %a, i32 %b, i32* %dst) {
 
 define i32 @and_not_xor_common_op(i32 %a, i32 %b) {
 ; CHECK-LABEL: @and_not_xor_common_op(
-; CHECK-NEXT:    [[B2:%.*]] = xor i32 [[B:%.*]], [[A:%.*]]
-; CHECK-NEXT:    [[T2:%.*]] = xor i32 [[B2]], -1
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[T2]], [[A]]
+; CHECK-NEXT:    [[T4:%.*]] = and i32 [[A:%.*]], [[B:%.*]]
 ; CHECK-NEXT:    ret i32 [[T4]]
 ;
   %b2 = xor i32 %b, %a
@@ -131,9 +129,7 @@ declare i32 @gen32()
 define i32 @and_not_xor_common_op_commutative(i32 %b) {
 ; CHECK-LABEL: @and_not_xor_common_op_commutative(
 ; CHECK-NEXT:    [[A:%.*]] = call i32 @gen32()
-; CHECK-NEXT:    [[B2:%.*]] = xor i32 [[A]], [[B:%.*]]
-; CHECK-NEXT:    [[T2:%.*]] = xor i32 [[B2]], -1
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[A]], [[T2]]
+; CHECK-NEXT:    [[T4:%.*]] = and i32 [[A]], [[B:%.*]]
 ; CHECK-NEXT:    ret i32 [[T4]]
 ;
   %a = call i32 @gen32()