[llvm] [AMDGPU] Simplify and improve codegen for llvm.amdgcn.set.inactive (PR #107889)

[Jay Foad via llvm-commits]

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@@ -145,15 +137,16 @@ define amdgpu_kernel void @set_inactive_scc(ptr addrspace(1) %out, i32 %in, <4 x
 define amdgpu_kernel void @set_inactive_f32(ptr addrspace(1) %out, float %in) {
 ; GCN-LABEL: set_inactive_f32:
 ; GCN:       ; %bb.0:
-; GCN-NEXT:    s_load_dword s6, s[2:3], 0x2c
+; GCN-NEXT:    s_load_dword s4, s[2:3], 0x2c
 ; GCN-NEXT:    s_load_dwordx2 s[0:1], s[2:3], 0x24
-; GCN-NEXT:    s_or_saveexec_b64 s[4:5], -1
+; GCN-NEXT:    s_or_saveexec_b64 s[2:3], -1
 ; GCN-NEXT:    v_mov_b32_e32 v0, 0x40400000
+; GCN-NEXT:    s_mov_b64 exec, s[2:3]
 ; GCN-NEXT:    s_mov_b32 s2, -1
-; GCN-NEXT:    s_mov_b64 exec, s[4:5]
 ; GCN-NEXT:    s_waitcnt lgkmcnt(0)
-; GCN-NEXT:    v_mov_b32_e32 v0, s6
-; GCN-NEXT:    s_mov_b64 exec, -1
+; GCN-NEXT:    v_mov_b32_e32 v1, s4
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jayfoad wrote:

This v_mov_b32 is an extra instruction due to constant bus restrictions in v_cndmask_b32 but these go away in GFX10+, and it is a pretty minor penalty anyway.

https://github.com/llvm/llvm-project/pull/107889