[InstCombine] fold logical and/or to xor

(A | B) & ~(A & B) --> A ^ B https://alive2.llvm.org/ce/z/qpFMns We already have the equivalent fold for real logic instructions, but this pattern may occur with selects too. This is part of solving issue #58313.
llvm · Oct 13, 2022 · d85505a · d85505a
1 parent b78306c
commit d85505a
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Showing 2 changed files with 9 additions and 11 deletions.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2774,6 +2774,11 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
         match(TrueVal, m_Specific(B)) && match(FalseVal, m_Zero()))
       return replaceOperand(SI, 0, A);
 
+    // ~(A & B) & (A | B) --> A ^ B
+    if (match(&SI, m_c_LogicalAnd(m_Not(m_LogicalAnd(m_Value(A), m_Value(B))),
+                                  m_c_LogicalOr(m_Deferred(A), m_Deferred(B)))))
+      return BinaryOperator::CreateXor(A, B);
+
     Value *C;
     // select (~a | c), a, b -> and a, (or c, freeze(b))
     if (match(CondVal, m_c_Or(m_Not(m_Specific(TrueVal)), m_Value(C))) &&

diff --git a/llvm/test/Transforms/InstCombine/logical-select.ll b/llvm/test/Transforms/InstCombine/logical-select.ll
@@ -932,10 +932,7 @@ define i8 @sext_cond_extra_uses(i1 %cmp, i8 %a, i8 %b) {
 
 define i1 @xor_commute0(i1 %x, i1 %y) {
 ; CHECK-LABEL: @xor_commute0(
-; CHECK-NEXT:    [[AND:%.*]] = select i1 [[X:%.*]], i1 [[Y:%.*]], i1 false
-; CHECK-NEXT:    [[OR:%.*]] = select i1 [[X]], i1 true, i1 [[Y]]
-; CHECK-NEXT:    [[NAND:%.*]] = xor i1 [[AND]], true
-; CHECK-NEXT:    [[AND2:%.*]] = select i1 [[NAND]], i1 [[OR]], i1 false
+; CHECK-NEXT:    [[AND2:%.*]] = xor i1 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    ret i1 [[AND2]]
 ;
   %and = select i1 %x, i1 %y, i1 false
@@ -948,10 +945,9 @@ define i1 @xor_commute0(i1 %x, i1 %y) {
 define i1 @xor_commute1(i1 %x, i1 %y) {
 ; CHECK-LABEL: @xor_commute1(
 ; CHECK-NEXT:    [[AND:%.*]] = select i1 [[X:%.*]], i1 [[Y:%.*]], i1 false
-; CHECK-NEXT:    [[OR:%.*]] = select i1 [[Y]], i1 true, i1 [[X]]
 ; CHECK-NEXT:    [[NAND:%.*]] = xor i1 [[AND]], true
 ; CHECK-NEXT:    call void @use1(i1 [[NAND]])
-; CHECK-NEXT:    [[AND2:%.*]] = select i1 [[NAND]], i1 [[OR]], i1 false
+; CHECK-NEXT:    [[AND2:%.*]] = xor i1 [[X]], [[Y]]
 ; CHECK-NEXT:    ret i1 [[AND2]]
 ;
   %and = select i1 %x, i1 %y, i1 false
@@ -970,7 +966,7 @@ define i1 @xor_commute2(i1 %x, i1 %y) {
 ; CHECK-NEXT:    call void @use1(i1 [[OR]])
 ; CHECK-NEXT:    [[NAND:%.*]] = xor i1 [[AND]], true
 ; CHECK-NEXT:    call void @use1(i1 [[NAND]])
-; CHECK-NEXT:    [[AND2:%.*]] = select i1 [[OR]], i1 [[NAND]], i1 false
+; CHECK-NEXT:    [[AND2:%.*]] = xor i1 [[X]], [[Y]]
 ; CHECK-NEXT:    ret i1 [[AND2]]
 ;
   %and = select i1 %x, i1 %y, i1 false
@@ -985,10 +981,7 @@ define i1 @xor_commute2(i1 %x, i1 %y) {
 
 define <2 x i1> @xor_commute3(<2 x i1> %x, <2 x i1> %y) {
 ; CHECK-LABEL: @xor_commute3(
-; CHECK-NEXT:    [[AND:%.*]] = select <2 x i1> [[X:%.*]], <2 x i1> [[Y:%.*]], <2 x i1> zeroinitializer
-; CHECK-NEXT:    [[OR:%.*]] = select <2 x i1> [[Y]], <2 x i1> <i1 true, i1 true>, <2 x i1> [[X]]
-; CHECK-NEXT:    [[NAND:%.*]] = xor <2 x i1> [[AND]], <i1 true, i1 true>
-; CHECK-NEXT:    [[AND2:%.*]] = select <2 x i1> [[OR]], <2 x i1> [[NAND]], <2 x i1> zeroinitializer
+; CHECK-NEXT:    [[AND2:%.*]] = xor <2 x i1> [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    ret <2 x i1> [[AND2]]
 ;
   %and = select <2 x i1> %x, <2 x i1> %y, <2 x i1> <i1 false, i1 false>