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

[Chen Zheng via llvm-commits]

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@@ -750,25 +750,21 @@ entry:
 define <2 x double> @testDoubleImm1(<2 x double> %a, double %b) {
 ; CHECK-64-LABEL: testDoubleImm1:
 ; CHECK-64:       # %bb.0: # %entry
-; CHECK-64-NEXT:    # kill: def $f1 killed $f1 def $vsl1
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chenzheng1030 wrote:

> However, I'm not sure if the implicit-def is necessary here or not.

Maybe the implicit-def is still necessary at least for the case where the other part of the super register is not allocatable, i.e., once f1 is defined, the vsl1 should also be defined as the phony part can not be allocated.

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