[InstSimplify] Simplify the expression (a^c)&(a^~c) to zero and (a^c) | (a^~c) to minus one (#76637)

Changes the InstSimplify pass of the LLVM optimizer, such that the
aforementioned expression is reduced to zero if c2==~c1.
Alive2: https://alive2.llvm.org/ce/z/xkQiid
Fixes #75692.

Author: ChipsSpectre

llvm/lib/Analysis/InstructionSimplify.cpp

@@ -2204,6 +2204,13 @@ static Value *simplifyAndInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
       match(Op1, m_c_Xor(m_Specific(Or), m_Specific(Y))))
     return Constant::getNullValue(Op0->getType());
 
+  const APInt *C1;
+  Value *A;
+  // (A ^ C) & (A ^ ~C) -> 0
+  if (match(Op0, m_Xor(m_Value(A), m_APInt(C1))) &&
+      match(Op1, m_Xor(m_Specific(A), m_SpecificInt(~*C1))))
+    return Constant::getNullValue(Op0->getType());
+
   if (Op0->getType()->isIntOrIntVectorTy(1)) {
     if (std::optional<bool> Implied = isImpliedCondition(Op0, Op1, Q.DL)) {
       // If Op0 is true implies Op1 is true, then Op0 is a subset of Op1.
@@ -2473,6 +2480,11 @@ static Value *simplifyOrInst(Value *Op0, Value *Op1, const SimplifyQuery &Q,
     if (Value *V = threadBinOpOverPHI(Instruction::Or, Op0, Op1, Q, MaxRecurse))
       return V;
 
+  // (A ^ C) | (A ^ ~C) -> -1, i.e. all bits set to one.
+  if (match(Op0, m_Xor(m_Value(A), m_APInt(C1))) &&
+      match(Op1, m_Xor(m_Specific(A), m_SpecificInt(~*C1))))
+    return Constant::getAllOnesValue(Op0->getType());
+
   if (Op0->getType()->isIntOrIntVectorTy(1)) {
     if (std::optional<bool> Implied =
             isImpliedCondition(Op0, Op1, Q.DL, false)) {

llvm/test/Transforms/InstCombine/and-xor-merge.ll

@@ -40,3 +40,42 @@ define i32 @PR38781(i32 %a, i32 %b) {
   %and = and i32 %b.lobit.not, %a.lobit.not
   ret i32 %and
 }
+
+; (a ^ 4) & (a ^ ~4) -> 0
+define i32 @PR75692_1(i32 %x) {
+; CHECK-LABEL: @PR75692_1
+; CHECK-NEXT:  ret i32 0
+;
+  %t2 = xor i32 %x, 4
+  %t3 = xor i32 %x, -5
+  %t4 = and i32 %t2, %t3
+  ret i32 %t4
+}
+
+; (a ^ 4) & (a ^ 3) is not zero
+define i32 @PR75692_2(i32 %x) {
+; CHECK-LABEL: @PR75692_2
+; CHECK-NEXT:  %t2 = xor i32 %x, 4
+; CHECK-NEXT:  %t3 = xor i32 %x, -4
+; CHECK-NEXT:  %t4 = and i32 %t2, %t3
+; CHECK-NEXT:  ret i32 %t4
+;
+  %t2 = xor i32 %x, 4
+  %t3 = xor i32 %x, -4
+  %t4 = and i32 %t2, %t3
+  ret i32 %t4
+}
+
+; (a ^ 4) & (b ^ ~4) is not zero, since a != b is possible
+define i32 @PR75692_3(i32 %x, i32 %y) {
+; CHECK-LABEL: @PR75692_3
+; CHECK-NEXT:  %t2 = xor i32 %x, 4
+; CHECK-NEXT:  %t3 = xor i32 %y, -5
+; CHECK-NEXT:  %t4 = and i32 %t2, %t3
+; CHECK-NEXT:  ret i32 %t4
+;
+  %t2 = xor i32 %x, 4
+  %t3 = xor i32 %y, -5
+  %t4 = and i32 %t2, %t3
+  ret i32 %t4
+}

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

@@ -1055,3 +1055,42 @@ define i8 @or_nand_xor_common_op_commute3_use3(i8 %x, i8 %y, i8 %z) {
   %r = or i8 %xor, %nand
   ret i8 %r
 }
+
+; (a ^ 4) & (a ^ ~4) -> -1
+define i32 @PR75692_1(i32 %x) {
+; CHECK-LABEL: @PR75692_1(
+; CHECK-NEXT:  ret i32 -1
+;
+  %t2 = xor i32 %x, 4
+  %t3 = xor i32 %x, -5
+  %t4 = or i32 %t2, %t3
+  ret i32 %t4
+}
+
+; (a ^ 4) & (a ^ 3) is not -1
+define i32 @PR75692_2(i32 %x) {
+; CHECK-LABEL: @PR75692_2
+; CHECK-NEXT:  %t2 = xor i32 %x, 4
+; CHECK-NEXT:  %t3 = xor i32 %x, -4
+; CHECK-NEXT:  %t4 = or i32 %t2, %t3
+; CHECK-NEXT:  ret i32 %t4
+;
+  %t2 = xor i32 %x, 4
+  %t3 = xor i32 %x, -4
+  %t4 = or i32 %t2, %t3
+  ret i32 %t4
+}
+
+; (a ^ 4) & (b ^ ~4) is not -1, since a != b is possible
+define i32 @PR75692_3(i32 %x, i32 %y) {
+; CHECK-LABEL: @PR75692_3
+; CHECK-NEXT:  %t2 = xor i32 %x, 4
+; CHECK-NEXT:  %t3 = xor i32 %y, -5
+; CHECK-NEXT:  %t4 = or i32 %t2, %t3
+; CHECK-NEXT:  ret i32 %t4
+;
+  %t2 = xor i32 %x, 4
+  %t3 = xor i32 %y, -5
+  %t4 = or i32 %t2, %t3
+  ret i32 %t4
+}