[InstCombine] Fix worklist management in select fold (#77738)

`InstCombine` uses `Worklist` to manage change history. `setOperand`,
which was previously used to change the `Select` Instruction, does not,
so it is `run` twice, which causes an `LLVM ERROR`.

This problem is resolved by changing `setOperand` to `replaceOperand` as
the change history will be registered in the Worklist.

Fixes #77553.

Author: ParkHanbum

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

@@ -1704,11 +1704,11 @@ Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
   if (CmpRHS != CmpLHS && isa<Constant>(CmpRHS) && !isa<Constant>(CmpLHS)) {
     if (CmpLHS == TrueVal && Pred == ICmpInst::ICMP_EQ) {
       // Transform (X == C) ? X : Y -> (X == C) ? C : Y
-      SI.setOperand(1, CmpRHS);
+      replaceOperand(SI, 1, CmpRHS);
       Changed = true;
     } else if (CmpLHS == FalseVal && Pred == ICmpInst::ICMP_NE) {
       // Transform (X != C) ? Y : X -> (X != C) ? Y : C
-      SI.setOperand(2, CmpRHS);
+      replaceOperand(SI, 2, CmpRHS);
       Changed = true;
     }
   }

llvm/test/Transforms/InstCombine/select.ll

@@ -3658,3 +3658,17 @@ loop:
 exit:
   ret i32 %rem
 }
+
+; (X == C) ? X : Y -> (X == C) ? C : Y
+; Fixed #77553
+define i32 @src_select_xxory_eq0_xorxy_y(i32 %x, i32 %y) {
+; CHECK-LABEL: @src_select_xxory_eq0_xorxy_y(
+; CHECK-NEXT:    [[XOR0:%.*]] = icmp eq i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[COND:%.*]] = select i1 [[XOR0]], i32 0, i32 [[Y]]
+; CHECK-NEXT:    ret i32 [[COND]]
+;
+  %xor = xor i32 %x, %y
+  %xor0 = icmp eq i32 %xor, 0
+  %cond = select i1 %xor0, i32 %xor, i32 %y
+  ret i32 %cond
+}