[llvm] [DAG] Fold build_vector(build_pair()) patterns. (PR #88261)

[Matt Arsenault via llvm-commits]

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@@ -197,14 +185,8 @@ define amdgpu_ps void @buffer_ptr_atomic_fadd_v2f16_offen_no_rtn(<2 x half> %val
   ; GFX908-NEXT:   [[COPY4:%[0-9]+]]:sgpr_32 = COPY $sgpr1
   ; GFX908-NEXT:   [[COPY5:%[0-9]+]]:sgpr_32 = COPY $sgpr0
   ; GFX908-NEXT:   [[COPY6:%[0-9]+]]:vgpr_32 = COPY $vgpr0
-  ; GFX908-NEXT:   [[REG_SEQUENCE:%[0-9]+]]:sgpr_64 = REG_SEQUENCE [[COPY3]], %subreg.sub0, [[COPY2]], %subreg.sub1
-  ; GFX908-NEXT:   [[COPY7:%[0-9]+]]:sreg_32 = COPY [[REG_SEQUENCE]].sub1
-  ; GFX908-NEXT:   [[COPY8:%[0-9]+]]:sreg_32 = COPY [[REG_SEQUENCE]].sub0
-  ; GFX908-NEXT:   [[REG_SEQUENCE1:%[0-9]+]]:sgpr_64 = REG_SEQUENCE [[COPY5]], %subreg.sub0, [[COPY4]], %subreg.sub1
-  ; GFX908-NEXT:   [[COPY9:%[0-9]+]]:sreg_32 = COPY [[REG_SEQUENCE1]].sub1
-  ; GFX908-NEXT:   [[COPY10:%[0-9]+]]:sreg_32 = COPY [[REG_SEQUENCE1]].sub0
-  ; GFX908-NEXT:   [[REG_SEQUENCE2:%[0-9]+]]:sgpr_128 = REG_SEQUENCE killed [[COPY10]], %subreg.sub0, killed [[COPY9]], %subreg.sub1, killed [[COPY8]], %subreg.sub2, killed [[COPY7]], %subreg.sub3
-  ; GFX908-NEXT:   BUFFER_ATOMIC_PK_ADD_F16_OFFEN [[COPY6]], [[COPY1]], killed [[REG_SEQUENCE2]], [[COPY]], 0, 0, implicit $exec :: (volatile dereferenceable load store (s32) on %ir.rsrc, align 1, addrspace 8)
+  ; GFX908-NEXT:   [[REG_SEQUENCE:%[0-9]+]]:sgpr_128 = REG_SEQUENCE [[COPY5]], %subreg.sub0, [[COPY4]], %subreg.sub1, [[COPY3]], %subreg.sub2, [[COPY2]], %subreg.sub3
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arsenm wrote:

These are all nice simplifications 

https://github.com/llvm/llvm-project/pull/88261