[llvm] [CodeGen] Fix handling dead redefs in finalizeBundle (PR #157427)

[Matt Arsenault via llvm-commits]

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@@ -8,7 +8,7 @@
 # The arguments to the call must become implicit arguments, because the branch
 # only expects to get 1 explicit operand which is the branch target.
 
-# CHECK:    BUNDLE implicit-def $lr, implicit-def $sp, implicit $sp, implicit $x0, implicit $w1 {
+# CHECK:    BUNDLE implicit-def dead $lr, implicit-def $sp, implicit $sp, implicit $x0, implicit $w1 {
 # CHECK:      BL @_setjmp, csr_aarch64_aapcs, implicit-def $lr, implicit $sp, implicit $x0, implicit $w1, implicit-def dead $lr, implicit $sp, implicit-def $sp
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arsenm wrote:

There's a definite lack of rules about how to interpret dead flags. In particular I don't know what dead means when you have aliasing register defs with mixed dead flags 

https://github.com/llvm/llvm-project/pull/157427