[InstCombine] Fold xor of bittests intto bittest of xor'd values

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

@@ -4150,9 +4150,6 @@ Value *InstCombinerImpl::foldXorOfICmps(ICmpInst *LHS, ICmpInst *RHS,
     }
   }
 
-  // TODO: This can be generalized to compares of non-signbits using
-  // decomposeBitTestICmp(). It could be enhanced more by using (something like)
-  // foldLogOpOfMaskedICmps().
   const APInt *LC, *RC;
   if (match(LHS1, m_APInt(LC)) && match(RHS1, m_APInt(RC)) &&
       LHS0->getType() == RHS0->getType() &&
@@ -4200,6 +4197,21 @@ Value *InstCombinerImpl::foldXorOfICmps(ICmpInst *LHS, ICmpInst *RHS,
           }
         }
     }
+
+    // Fold (icmp eq/ne (X & Pow2), 0) ^ (icmp eq/ne (Y & Pow2), 0) into
+    // (icmp eq/ne ((X ^ Y) & Pow2), 0)
+    Value *X, *Y;
+    const APInt *Mask;
+    if (ICmpInst::isEquality(PredL) && ICmpInst::isEquality(PredR) &&
+        LC->isZero() && RC->isZero() && LHS->hasOneUse() && RHS->hasOneUse() &&
+        match(LHS0, m_And(m_Value(X), m_Power2(Mask))) &&
+        match(RHS0, m_And(m_Value(Y), m_SpecificInt(*Mask)))) {
+      Value *Xor = Builder.CreateXor(X, Y);
+      Value *And = Builder.CreateAnd(Xor, *Mask);
+      return Builder.CreateICmp(PredL == PredR ? ICmpInst::ICMP_NE
+                                               : ICmpInst::ICMP_EQ,
+                                And, ConstantInt::getNullValue(Xor->getType()));
+    }
   }
 
   // Instead of trying to imitate the folds for and/or, decompose this 'xor'

llvm/test/Transforms/InstCombine/xor-icmps.ll

@@ -322,12 +322,10 @@ define i1 @xor_icmp_to_icmp_add_multiuse2(i32 %a) {
 
 define i1 @test_xor_of_bittest_ne_ne(i8 %x, i8 %y) {
 ; CHECK-LABEL: @test_xor_of_bittest_ne_ne(
-; CHECK-NEXT:    [[MASK1:%.*]] = and i8 [[X:%.*]], 2
-; CHECK-NEXT:    [[CMP1:%.*]] = icmp ne i8 [[MASK1]], 0
-; CHECK-NEXT:    [[MASK2:%.*]] = and i8 [[Y:%.*]], 2
+; CHECK-NEXT:    [[Y:%.*]] = xor i8 [[X:%.*]], [[Y1:%.*]]
+; CHECK-NEXT:    [[MASK2:%.*]] = and i8 [[Y]], 2
 ; CHECK-NEXT:    [[CMP2:%.*]] = icmp ne i8 [[MASK2]], 0
-; CHECK-NEXT:    [[XOR:%.*]] = xor i1 [[CMP1]], [[CMP2]]
-; CHECK-NEXT:    ret i1 [[XOR]]
+; CHECK-NEXT:    ret i1 [[CMP2]]
 ;
   %mask1 = and i8 %x, 2
   %cmp1 = icmp ne i8 %mask1, 0
@@ -339,11 +337,9 @@ define i1 @test_xor_of_bittest_ne_ne(i8 %x, i8 %y) {
 
 define i1 @test_xor_of_bittest_eq_eq(i8 %x, i8 %y) {
 ; CHECK-LABEL: @test_xor_of_bittest_eq_eq(
-; CHECK-NEXT:    [[MASK1:%.*]] = and i8 [[X:%.*]], 2
-; CHECK-NEXT:    [[CMP1:%.*]] = icmp eq i8 [[MASK1]], 0
-; CHECK-NEXT:    [[MASK2:%.*]] = and i8 [[Y:%.*]], 2
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp eq i8 [[MASK2]], 0
-; CHECK-NEXT:    [[XOR:%.*]] = xor i1 [[CMP1]], [[CMP2]]
+; CHECK-NEXT:    [[Y:%.*]] = xor i8 [[X:%.*]], [[Y1:%.*]]
+; CHECK-NEXT:    [[MASK2:%.*]] = and i8 [[Y]], 2
+; CHECK-NEXT:    [[XOR:%.*]] = icmp ne i8 [[MASK2]], 0
 ; CHECK-NEXT:    ret i1 [[XOR]]
 ;
   %mask1 = and i8 %x, 2
@@ -356,12 +352,10 @@ define i1 @test_xor_of_bittest_eq_eq(i8 %x, i8 %y) {
 
 define i1 @test_xor_of_bittest_ne_eq(i8 %x, i8 %y) {
 ; CHECK-LABEL: @test_xor_of_bittest_ne_eq(
-; CHECK-NEXT:    [[MASK1:%.*]] = and i8 [[X:%.*]], 2
-; CHECK-NEXT:    [[CMP1:%.*]] = icmp ne i8 [[MASK1]], 0
-; CHECK-NEXT:    [[MASK2:%.*]] = and i8 [[Y:%.*]], 2
+; CHECK-NEXT:    [[Y:%.*]] = xor i8 [[X:%.*]], [[Y1:%.*]]
+; CHECK-NEXT:    [[MASK2:%.*]] = and i8 [[Y]], 2
 ; CHECK-NEXT:    [[CMP2:%.*]] = icmp eq i8 [[MASK2]], 0
-; CHECK-NEXT:    [[XOR:%.*]] = xor i1 [[CMP1]], [[CMP2]]
-; CHECK-NEXT:    ret i1 [[XOR]]
+; CHECK-NEXT:    ret i1 [[CMP2]]
 ;
   %mask1 = and i8 %x, 2
   %cmp1 = icmp ne i8 %mask1, 0
@@ -373,12 +367,10 @@ define i1 @test_xor_of_bittest_ne_eq(i8 %x, i8 %y) {
 
 define i1 @test_xor_of_bittest_eq_ne(i8 %x, i8 %y) {
 ; CHECK-LABEL: @test_xor_of_bittest_eq_ne(
-; CHECK-NEXT:    [[MASK1:%.*]] = and i8 [[X:%.*]], 2
+; CHECK-NEXT:    [[X:%.*]] = xor i8 [[X1:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[MASK1:%.*]] = and i8 [[X]], 2
 ; CHECK-NEXT:    [[CMP1:%.*]] = icmp eq i8 [[MASK1]], 0
-; CHECK-NEXT:    [[MASK2:%.*]] = and i8 [[Y:%.*]], 2
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp ne i8 [[MASK2]], 0
-; CHECK-NEXT:    [[XOR:%.*]] = xor i1 [[CMP1]], [[CMP2]]
-; CHECK-NEXT:    ret i1 [[XOR]]
+; CHECK-NEXT:    ret i1 [[CMP1]]
 ;
   %mask1 = and i8 %x, 2
   %cmp1 = icmp eq i8 %mask1, 0
@@ -392,11 +384,11 @@ define i1 @test_xor_of_bittest_ne_ne_multiuse1(i8 %x, i8 %y) {
 ; CHECK-LABEL: @test_xor_of_bittest_ne_ne_multiuse1(
 ; CHECK-NEXT:    [[MASK1:%.*]] = and i8 [[X:%.*]], 2
 ; CHECK-NEXT:    call void @usei8(i8 [[MASK1]])
-; CHECK-NEXT:    [[CMP1:%.*]] = icmp ne i8 [[MASK1]], 0
 ; CHECK-NEXT:    [[MASK2:%.*]] = and i8 [[Y:%.*]], 2
 ; CHECK-NEXT:    call void @usei8(i8 [[MASK2]])
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp ne i8 [[MASK2]], 0
-; CHECK-NEXT:    [[XOR:%.*]] = xor i1 [[CMP1]], [[CMP2]]
+; CHECK-NEXT:    [[TMP1:%.*]] = xor i8 [[X]], [[Y]]
+; CHECK-NEXT:    [[TMP2:%.*]] = and i8 [[TMP1]], 2
+; CHECK-NEXT:    [[XOR:%.*]] = icmp ne i8 [[TMP2]], 0
 ; CHECK-NEXT:    ret i1 [[XOR]]
 ;
   %mask1 = and i8 %x, 2