[llvm] [RISCV] Remove x7 from fastcc list. (PR #96729)

[Craig Topper via llvm-commits]

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@@ -18696,13 +18696,12 @@ static ArrayRef<MCPhysReg> getFastCCArgGPRs(const RISCVABI::ABI ABI) {
   // for save-restore libcall, so we don't use them.
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topperc wrote:

Please update the comment to indicate why we don't use X7.

https://github.com/llvm/llvm-project/pull/96729