[llvm] [clang] [PowerPC] Make "ca" aliased to "xer" (PR #77557)

[Kai Luo via cfe-commits]

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@@ -782,6 +782,8 @@ ArrayRef<const char *> PPCTargetInfo::getGCCRegNames() const {
 const TargetInfo::GCCRegAlias PPCTargetInfo::GCCRegAliases[] = {
     // While some of these aliases do map to different registers
     // they still share the same register name.
+    // Strictly speaking, "ca" is a subregister of "xer". However currently we
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bzEq wrote:

> If that happens, would we have to add those other fields and then specify them as proper subregs of XER?

I think so. However, existing instructions look not using other fields like OV and OV32.

> does GCC support on PowerPC?

Currently, GCC looks only support `xer` and `ca`. See https://godbolt.org/z/6qWqc3Pdd. I have tried using `ov`, hit CE.

https://github.com/llvm/llvm-project/pull/77557