[llvm] [PowerPC] Add phony subregisters to cover the high half of the VSX registers. (PR #94628)

[Chen Zheng via llvm-commits]

================
@@ -168,17 +181,19 @@ foreach Index = 0-31 in {
                  DwarfRegNum<[!add(Index, 77), !add(Index, 77)]>;
 }
 
+let CoveredBySubRegs = 1 in {
 // Vector registers
 foreach Index = 0-31 in {
-  def V#Index : VR<!cast<VF>("VF"#Index), "v"#Index>,
-                DwarfRegNum<[!add(Index, 77), !add(Index, 77)]>;
+  def V#Index : VR<!cast<VF>("VF"#Index), !cast<VF>("VFH"#Index), "v"#Index>,
+                DwarfRegNum<[!add(Index, 77)]>;
----------------
chenzheng1030 wrote:

Why we remove the second `!add(Index, 77)`? I think it is still needed for 32/64 bit?

https://github.com/llvm/llvm-project/pull/94628