[clang] [llvm] [AMDGPU] Add initial support for VGPR as memory (PR #205435)

[Matt Arsenault via llvm-commits]

================
@@ -319,6 +319,11 @@ def warn_stack_protection_ignore_attribute : Warning<
   "'stack_protector_ignore' attribute ignored due to "
   "'-fstack-protector-all' option">, InGroup<IgnoredAttributes>;
 
+def warn_amdgpu_vgpr_not_guaranteed_at_O0 : Warning<
+  "%0 is not guaranteed to keep the variable in vector registers at -O0; "
+  "it may fall back to scratch memory">,
----------------
arsenm wrote:

This is a design flaw. It can't be guaranteed at any optimization level. It either needs to be an explicit, mandatory allocation, or there's no point 

https://github.com/llvm/llvm-project/pull/205435