RISC-V: Use symbolic instructions on inline assembly (part 2) #1936
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While many intrinsics use `.insn` to generate raw machine code from numbers, all ratified instructions can be symbolic using `.option` directives. By saving the assembler environment with `.option push` then modifying the architecture with `.option arch`, we can temporarily enable certain extensions (as we use `.option pop` immediately after the target instruction, surrounding environment is completely intact in this commit; *almost* completely intact in general). This commit modifies the `pause` *hint* intrinsic to use symbolic *instruction* because we want to expose it even if the Zihintpause extension is unavailable on the target.
While many intrinsics use `.insn` to generate raw machine code from numbers, all ratified instructions can be now symbolic. This is the part two (after the `pause` intrinsic) and uses a different way to use symbolic instructions. Normally, intrinsics require corresponding extensions and this commit uses newly added Rust target features `h` and `svinval` (both representing supervisor-mode extensions), along with the `#[target_feature(enable = ...)]` attribute. Note: `hinval.vvma` and `hinval.gvma` instructions are a part of the Svinval extension (the H extension is not directly required by LLVM) but denoted to require both `h` and `svinval` to show semantic context (they are useful only when the H extension is present and according to the documentation, they are provided only if the hypervisor extension is enabled).
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While many intrinsics use
.insnto generate raw machine code from numbers, all ratified instructions can be now symbolic.This is the part two (after the
pauseintrinsic) and uses a different way to use symbolic instructions.Normally, intrinsics require corresponding extensions and this commit uses newly added Rust target features
handsvinval(both representing supervisor-mode extensions), along with the#[target_feature(enable = ...)]attribute.Note
hinval.vvmaandhinval.gvmainstructions are a part of the Svinval extension (the H extension is not directly required by LLVM) but denoted to require bothhandsvinvalto show semantic context (they are useful only when the H extension is present and according to the documentation, they are provided only if the hypervisor extension is enabled).This is the part two after #1927 (currently, this is the superset of it) and requires some Rust compiler changes (adding target features
handsvinval; so CI should fail as of this writing).