[llvm] [AMDGPU][GISEL] Marking G_DYN_STACKALLOC AlwaysUniform in uniformity analysis (PR #200390)

[Abhinav Garg via llvm-commits]

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@@ -55,3 +55,25 @@ body:             |
     %1:vgpr_32 = COPY $sgpr1
     S_ENDPGM 0
 ...
+
+# G_DYN_STACKALLOC result is always uniform. The returned value is computed
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abhigargrepo wrote:

always-uniform-gmir.mir test file has a comment "_This file is Generic MIR translation of test/Analysis/UniformityAnalysis/AMDGPU/always_uniform.ll test file_"
Actually I tried to add test in that file first but found always-uniform.mir to be better place.

https://github.com/llvm/llvm-project/pull/200390