[llvm] [RISCV] Support floating point registers with -fzero-call-used-regs (PR #204929)

[Sam Elliott via llvm-commits]

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@@ -24,6 +25,7 @@ CCAssignFn RetCC_RISCV;
 namespace RISCV {
 
 ArrayRef<MCPhysReg> getArgGPRs(const RISCVABI::ABI ABI);
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lenary wrote:

This is probably something for a follow-up NFC: can we align the signatures here so `getArgGPRs` takes a `const RISCVSubtarget &` too? I think one is available at all call-sites.

https://github.com/llvm/llvm-project/pull/204929