| Issue |
130006
|
| Summary |
Move MCSymbolRefExpr::VK_AMDGPU_ to AMDGPUMCExpr::
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
MaskRay
|
`MCSymbolRefExpr::VariantKind` isn't ideal for encoding relocation operators because:
* other expressions, like MCConstantExpr (e.g., PPC `4@l`) and MCBinaryExpr (e.g., PPC `(a+1)@l`), also need it
* semantics become unclear (e.g., folding expressions with `@`).
* The generic interface `MCSymbolRefExpr` offers no target-specific extension point. Any target-specific logic will pollute the generic interface.
`MCTargetExpr` subclasses, as used by AArch64 and RISC-V, offer a cleaner approach.
(MIPS, while also uses `MCTargetExpr`, has significant tech debt.)
Ideally, limit `MCTargetExpr` to top-level use to encode one single relocation and avoid its inclusion as a subexpression.
`AMDMCExpr::VariantKind` is already present. Should just move more `VK_AMDGPU_*` there. @arsenm
Similar issue for VE: #130003
---
AArch64 is a good model where the `VariantKind` information is incoded as `AArch64MCExpr` (derived from `MCTargetExpr`)
```
// llvm/lib/Target/AArch64/AArch64MCInstLower.cpp
Expr = AArch64MCExpr::create(Expr, RefKind, Ctx);
// llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
ImmVal = AArch64MCExpr::create(ImmVal, RefKind, getContext());
```
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