[llvm] [LoopIdiom] Use narrower bit widths where possible in `optimizeCRCLoopUsingClmul` (PR #210139)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -161,16 +161,17 @@ define i8 @crc8.le.tc16(i16 %msg, i8 %checksum) optsize {
 ; AES-LABEL: define i8 @crc8.le.tc16(
 ; AES-SAME: i16 [[MSG:%.*]], i8 [[CHECKSUM:%.*]]) #[[ATTR0]] {
 ; AES-NEXT:  [[ENTRY:.*:]]
-; AES-NEXT:    [[CRC_CAST:%.*]] = zext i8 [[CHECKSUM]] to i32
-; AES-NEXT:    [[DATA_CAST:%.*]] = zext i16 [[MSG]] to i32
-; AES-NEXT:    [[XOR_CRC_DATA1:%.*]] = xor i32 [[CRC_CAST]], [[DATA_CAST]]
-; AES-NEXT:    [[CRC_TCBITS:%.*]] = and i32 [[XOR_CRC_DATA1]], 65535
-; AES-NEXT:    [[CLMUL_MU:%.*]] = call i32 @llvm.clmul.i32(i32 [[CRC_TCBITS]], i32 24423)
+; AES-NEXT:    [[CRC_CAST:%.*]] = zext i8 [[CHECKSUM]] to i16
+; AES-NEXT:    [[XOR_CRC_DATA1:%.*]] = xor i16 [[CRC_CAST]], [[MSG]]
+; AES-NEXT:    [[TCBITS_CAST:%.*]] = zext i16 [[XOR_CRC_DATA1]] to i32
+; AES-NEXT:    [[CLMUL_MU:%.*]] = call i32 @llvm.clmul.i32(i32 [[TCBITS_CAST]], i32 24423)
 ; AES-NEXT:    [[QUOT_MASK:%.*]] = and i32 [[CLMUL_MU]], 65535
-; AES-NEXT:    [[CLMUL_GP:%.*]] = call i32 @llvm.clmul.i32(i32 [[QUOT_MASK]], i32 59)
-; AES-NEXT:    [[XOR_CRC_MULT:%.*]] = xor i32 [[CRC_CAST]], [[CLMUL_GP]]
-; AES-NEXT:    [[CRC_LSHR2:%.*]] = lshr i32 [[XOR_CRC_MULT]], 16
-; AES-NEXT:    [[CRC_NEXT3:%.*]] = trunc i32 [[CRC_LSHR2]] to i8
+; AES-NEXT:    [[QUOT_CAST:%.*]] = trunc i32 [[QUOT_MASK]] to i24
+; AES-NEXT:    [[CLMUL_GP:%.*]] = call i24 @llvm.clmul.i24(i24 [[QUOT_CAST]], i24 59)
+; AES-NEXT:    [[CRC_RECAST:%.*]] = zext i8 [[CHECKSUM]] to i24
+; AES-NEXT:    [[XOR_CRC_MULT:%.*]] = xor i24 [[CRC_RECAST]], [[CLMUL_GP]]
+; AES-NEXT:    [[CRC_LSHR2:%.*]] = lshr i24 [[XOR_CRC_MULT]], 16
+; AES-NEXT:    [[CRC_NEXT3:%.*]] = trunc i24 [[CRC_LSHR2]] to i8
----------------
artagnon wrote:

Equivalent to:

```llvm
%gp.cast = trunc i24 clmul.gp to i8 
xor i8 %checksum, %gp.cast
```

https://github.com/llvm/llvm-project/pull/210139