| Issue |
144869
|
| Summary |
SystemZ `esrl` instruction doesn't disassemble `%r0`
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
Rot127
|
The SystemZ disassembler doesn't decode `%r0` registers if they are part of an address.
```
echo "0xc6,0x00,0x00,0x00,0x00,0x05" | llvm-mc --disassemble --triple=s390x --show-encoding
.text
exrl 0, 0xa # encoding: [0xc6,0x00,A,A,A,A]
# fixup A - offset: 2, value: 12, kind: FK_390_PC32D
```
It should be `exrl %r0, 0xa`.
It does work the other way around though:
```
echo "exrl %r0, 0xa" | llvm-mc --assemble --triple=s390x --show-encoding
.text
.Ltmp0:
exrl %r0, .Ltmp0+10 # encoding: [0xc6,0x00,A,A,A,A]
# fixup A - offset: 2, value: (.Ltmp0+10)+2, kind: FK_390_PC32DBL
```
This might due to https://github.com/llvm/llvm-project/issues/44437.
Debugging shows that it happens due to these lines:
https://github.com/llvm/llvm-project/blob/1c35fe4e6b2596d153da82b23d04a3779fb12730/llvm/lib/Target/SystemZ/Disassembler/SystemZDisassembler.cpp#L87-L89
The given register table in `Regs` contains a the valid register id of `r0`, but here it ignores it.
It possibly was supposed to be?
```diff
{
assert(RegNo < Size && "Invalid register");
- if (IsAddr && RegNo == 0) {
+ if (IsAddr && Regs[RegNo] == 0) {
RegNo = SystemZ::NoRegister;
} else {
```
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