[CombToAIG] Use string substitution in a test, NFC

Author: uenoku

test/Conversion/CombToAIG/comb-to-aig-arith.mlir

@@ -34,11 +34,11 @@ hw.module @sub(in %lhs: i4, in %rhs: i4, out out: i4) {
 // ALLOW_ADD-NEXT:   %[[EXT_0:.+]] = comb.extract %lhs from 0 : (i2) -> i1
 // ALLOW_ADD-NEXT:   %[[EXT_1:.+]] = comb.extract %lhs from 1 : (i2) -> i1
 // ALLOW_ADD-NEXT:   %c0_i2 = hw.constant 0 : i2
-// ALLOW_ADD-NEXT:   %[[MUX_0:.+]] = comb.mux %0, %rhs, %c0_i2 : i2
-// ALLOW_ADD-NEXT:   %[[MUX_1:.+]] = comb.mux %1, %rhs, %c0_i2 : i2
-// ALLOW_ADD-NEXT:   %[[EXT_MUX_1:.+]] = comb.extract %3 from 0 : (i2) -> i1
+// ALLOW_ADD-NEXT:   %[[MUX_0:.+]] = comb.mux %[[EXT_0]], %rhs, %c0_i2 : i2
+// ALLOW_ADD-NEXT:   %[[MUX_1:.+]] = comb.mux %[[EXT_1]], %rhs, %c0_i2 : i2
+// ALLOW_ADD-NEXT:   %[[EXT_MUX_1:.+]] = comb.extract %[[MUX_1]] from 0 : (i2) -> i1
 // ALLOW_ADD-NEXT:   %false = hw.constant false
-// ALLOW_ADD-NEXT:   %[[SHIFT:.+]] = comb.concat %4, %false : i1, i1
+// ALLOW_ADD-NEXT:   %[[SHIFT:.+]] = comb.concat %[[EXT_MUX_1]], %false : i1, i1
 // ALLOW_ADD-NEXT:   %[[ADD:.+]] = comb.add bin %[[MUX_0]], %[[SHIFT]] : i2
 // ALLOW_ADD-NEXT:   hw.output %[[ADD]] : i2
 // ALLOW_ADD-NEXT: }