[InstCombine] Fold (select (icmp eq (and x, y), 0), (add/xor x, y), F)

In the context of `(icmp eq (and x, y), 0)` we can replace `add`/`xor`
with `or`:
https://alive2.llvm.org/ce/z/R7CQp3

Author: goldsteinn

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -4395,5 +4395,31 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
       return replaceOperand(SI, 2, ConstantInt::get(FalseVal->getType(), 0));
   }
 
+  {
+    // (select (icmp eq (and X, Y), 0), (add/xor X, Y), F)
+    //	-> (select (icmp eq (and X, Y), 0), (or X, Y), F)
+    // And vice versa for `ne` pred.
+    CmpPredicate Pred;
+    Value *X, *Y;
+    if (match(CondVal, m_ICmp(Pred, m_And(m_Value(X), m_Value(Y)), m_Zero())) &&
+        ICmpInst::isEquality(Pred)) {
+      unsigned RepIdx;
+      Value *RepArm;
+      if (Pred == CmpInst::ICMP_EQ) {
+        RepIdx = 1;
+        RepArm = TrueVal;
+      } else {
+        RepIdx = 2;
+        RepArm = FalseVal;
+      }
+      auto ReduceToOrNoCommonBits =
+          m_CombineOr(m_c_Xor(m_Specific(X), m_Specific(Y)),
+                      m_c_Add(m_Specific(X), m_Specific(Y)));
+
+      if (RepArm->hasOneUse() && match(RepArm, ReduceToOrNoCommonBits))
+        return replaceOperand(SI, RepIdx, Builder.CreateOr(X, Y));
+    }
+  }
+
   return nullptr;
 }

llvm/test/Transforms/InstCombine/select.ll

@@ -3787,12 +3787,8 @@ entry:
 define i32 @src_and_eq_0_xor_or(i32 %x, i32 %y) {
 ; CHECK-LABEL: @src_and_eq_0_xor_or(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[AND:%.*]] = and i32 [[Y:%.*]], [[X:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[AND]], 0
-; CHECK-NEXT:    [[XOR:%.*]] = xor i32 [[Y]], [[X]]
-; CHECK-NEXT:    [[OR:%.*]] = or i32 [[Y]], [[X]]
-; CHECK-NEXT:    [[COND:%.*]] = select i1 [[CMP]], i32 [[XOR]], i32 [[OR]]
-; CHECK-NEXT:    ret i32 [[COND]]
+; CHECK-NEXT:    [[OR:%.*]] = or i32 [[Y:%.*]], [[X:%.*]]
+; CHECK-NEXT:    ret i32 [[OR]]
 ;
 entry:
   %and = and i32 %y, %x
@@ -4428,7 +4424,7 @@ define i32 @src_no_trans_select_and_eq0_xor_and(i32 %x, i32 %y) {
 ; CHECK-LABEL: @src_no_trans_select_and_eq0_xor_and(
 ; CHECK-NEXT:    [[AND:%.*]] = and i32 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    [[AND0:%.*]] = icmp eq i32 [[AND]], 0
-; CHECK-NEXT:    [[XOR:%.*]] = xor i32 [[X]], [[Y]]
+; CHECK-NEXT:    [[XOR:%.*]] = or i32 [[X]], [[Y]]
 ; CHECK-NEXT:    [[COND:%.*]] = select i1 [[AND0]], i32 [[XOR]], i32 [[AND]]
 ; CHECK-NEXT:    ret i32 [[COND]]
 ;
@@ -4461,7 +4457,7 @@ define i32 @src_no_trans_select_and_eq0_add(i32 %x, i32 %y, i32 %z) {
 ; CHECK-NEXT:    [[AND:%.*]] = and i32 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    [[AND0:%.*]] = icmp ne i32 [[AND]], 0
 ; CHECK-NEXT:    call void @use.i1(i1 [[AND0]])
-; CHECK-NEXT:    [[ADD:%.*]] = add i32 [[X]], [[Y]]
+; CHECK-NEXT:    [[ADD:%.*]] = or i32 [[X]], [[Y]]
 ; CHECK-NEXT:    [[COND:%.*]] = select i1 [[AND0]], i32 [[Z:%.*]], i32 [[ADD]]
 ; CHECK-NEXT:    ret i32 [[COND]]
 ;