[HWArith] Make hwarith.icmp result an i1 (#7413)

As discussed in #7406. Resolves #7406.

docs/Dialects/HWArith/RationaleHWArith.md

@@ -483,19 +483,18 @@ can be simplified to:
 %4 = hwarith.icmp lt %0, %1 : si3, ui5
 ```
 
-Note that the result of the comparison is *always* of type `ui1`, regardless of
-the operands. So if the `i1` type is needed, the result must be cast
-accordingly.
+Note that the result of the comparison is *always* of type `i1` since the
+logical result is a boolean, which doesn't have signedness semantics.
 
 #### Overview
 
 |   | LHS type | RHS type | Comparison type                          | Result type |
 | - | :------- | :------- | :--------------------------------------- | :---------- |
-|(U)| `ui<a>`  | `ui<b>`  | `ui<r>`, *r* = max(*a*, *b*)             | `ui1`       |
-|(S)| `si<a>`  | `si<b>`  | `si<r>`, *r* = max(*a*, *b*)             | `ui1`       |
-|(M)| `ui<a>`  | `si<b>`  | `si<r>`, *r* = *a* + 1 **if** *a* ≥ *b*  | `ui1`       |
-|   |          |          | `si<r>`, *r* = *b* **if** *a* < *b*      | `ui1`       |
-|(M)| `si<a>`  | `ui<b>`  | Same as `ui<b> si<a>`                    | `ui1`       |
+|(U)| `ui<a>`  | `ui<b>`  | `ui<r>`, *r* = max(*a*, *b*)             | `i1`        |
+|(S)| `si<a>`  | `si<b>`  | `si<r>`, *r* = max(*a*, *b*)             | `i1`        |
+|(M)| `ui<a>`  | `si<b>`  | `si<r>`, *r* = *a* + 1 **if** *a* ≥ *b*  | `i1`        |
+|   |          |          | `si<r>`, *r* = *b* **if** *a* < *b*      | `i1`        |
+|(M)| `si<a>`  | `ui<b>`  | Same as `ui<b> si<a>`                    | `i1`        |
 
 #### Examples
 ```mlir

include/circt/Dialect/HWArith/HWArithOps.td

@@ -227,16 +227,16 @@ def ICmpOp : HWArithOp<"icmp", [Pure]> {
   let description = [{
     The `icmp` operation compares two integers using a predicate. If the
     predicate is true, returns 1, otherwise returns 0. This operation always
-    returns a one bit wide result of type `ui1`. Both operand types may be
+    returns a one bit wide result of type `i1`. Both operand types may be
     signed or unsigned scalar integer types of arbitrary bitwidth.
 
     | LHS type | RHS type | Comparison type                          | Result type |
     | :------- | :------- | :--------------------------------------- | :---------- |
-    | `ui<a>`  | `ui<b>`  | `ui<r>`, *r* = max(*a*, *b*)             | `ui1`       |
-    | `si<a>`  | `si<b>`  | `si<r>`, *r* = max(*a*, *b*)             | `ui1`       |
-    | `ui<a>`  | `si<b>`  | `si<r>`, *r* = *a* + 1 **if** *a* ≥ *b*  | `ui1`       |
-    |          |          | `si<r>`, *r* = *b* **if** *a* < *b*      | `ui1`       |
-    | `si<a>`  | `ui<b>`  | Same as `ui<b> si<a>`                    | `ui1`       |
+    | `ui<a>`  | `ui<b>`  | `ui<r>`, *r* = max(*a*, *b*)             | `i1`        |
+    | `si<a>`  | `si<b>`  | `si<r>`, *r* = max(*a*, *b*)             | `i1`        |
+    | `ui<a>`  | `si<b>`  | `si<r>`, *r* = *a* + 1 **if** *a* ≥ *b*  | `i1`        |
+    |          |          | `si<r>`, *r* = *b* **if** *a* < *b*      | `i1`        |
+    | `si<a>`  | `ui<b>`  | Same as `ui<b> si<a>`                    | `i1`        |
 
     Examples:
     ```mlir
@@ -248,7 +248,7 @@ def ICmpOp : HWArithOp<"icmp", [Pure]> {
 
   let arguments = (ins ICmpPredicate:$predicate,
                    HWArithIntegerType:$lhs, HWArithIntegerType:$rhs);
-  let results = (outs UI1:$result);
+  let results = (outs I1:$result);
 
   let assemblyFormat = "$predicate $lhs `,` $rhs  attr-dict `:` type($lhs) `,` type($rhs)";
 }

test/Conversion/HWArithToHW/test_basic.mlir

@@ -243,13 +243,8 @@ hw.module @icmp(in %op0: i32, in %op1: i32, out sisi: i1, out siui: i1, out uisi
 // CHECK:   %[[UIUI_OUT:.*]] = comb.icmp ult %op0, %op1 : i32
   %uiui = hwarith.icmp lt %op0Unsigned, %op1Unsigned : ui32, ui32
 
-  %sisiOut = hwarith.cast %sisi : (ui1) -> i1
-  %siuiOut = hwarith.cast %siui : (ui1) -> i1
-  %uisiOut = hwarith.cast %uisi : (ui1) -> i1
-  %uiuiOut = hwarith.cast %uiui : (ui1) -> i1
-
 // CHECK:   hw.output %[[SISI_OUT]], %[[SIUI_OUT]], %[[UISI_OUT]], %[[UIUI_OUT]] : i1, i1, i1, i1
-  hw.output %sisiOut, %siuiOut, %uisiOut, %uiuiOut : i1, i1, i1, i1
+  hw.output %sisi, %siui, %uisi, %uiui: i1, i1, i1, i1
 }
 
 // -----
@@ -285,13 +280,8 @@ hw.module @icmp_mixed_width(in %op0: i5, in %op1: i7, out sisi: i1, out siui: i1
 // CHECK:   %[[UIUI_OUT:.*]] = comb.icmp ult %[[OP0_PADDED]], %op1 : i7
   %uiui = hwarith.icmp lt %op0Unsigned, %op1Unsigned : ui5, ui7
 
-  %sisiOut = hwarith.cast %sisi : (ui1) -> i1
-  %siuiOut = hwarith.cast %siui : (ui1) -> i1
-  %uisiOut = hwarith.cast %uisi : (ui1) -> i1
-  %uiuiOut = hwarith.cast %uiui : (ui1) -> i1
-
 // CHECK:   hw.output %[[SISI_OUT]], %[[SIUI_OUT]], %[[UISI_OUT]], %[[UIUI_OUT]] : i1, i1, i1, i1
-  hw.output %sisiOut, %siuiOut, %uisiOut, %uiuiOut : i1, i1, i1, i1
+  hw.output %sisi, %siui, %uisi, %uiui: i1, i1, i1, i1
 }
 
 // -----

test/Dialect/HWArith/basic.mlir

@@ -33,6 +33,4 @@ hw.module @test1() {
   %12 = hwarith.cast %11 : (si10) -> i9
   // CHECK: %13 = hwarith.icmp eq %5, %10 : ui2, si9
   %13 = hwarith.icmp eq %5, %10 : ui2, si9
-  // CHECK: %14 = hwarith.cast %13 : (ui1) -> i1
-  %14 = hwarith.cast %13 : (ui1) -> i1
 }