[PATCH] D56305: [AArch64] Support reserving arbitrary general purpose registers

[Tri Vo via Phabricator via cfe-commits]

trong added inline comments.
Herald added a project: LLVM.


================
Comment at: clang/lib/Driver/ToolChains/Arch/AArch64.cpp:318
 
+  if (Args.hasArg(options::OPT_ffixed_x0))
+    Features.push_back("+reserve-x0");
----------------
phosek wrote:
> trong wrote:
> > What happens (should happen) if we reserve x0 and compile a function with a return value?
> Clang throws `error: AArch64 doesn't support function calls if any of the argument registers is reserved.` as for any other argument register.
Yes, if x0 is reserved, it can't be used to pass arguments. But what happens if x0 is used to return a value? For example:
```
int foo() {
    return 1;
}
```
It would be helpful if compiling `foo()` with x0 reserved threw an error.


Repository:
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  https://reviews.llvm.org/D56305/new/

https://reviews.llvm.org/D56305