[llvm] [AMDGPU] Legalize 64bit elements for BUILD_VECTOR on gfx942 (PR #145052)

[Janek van Oirschot via llvm-commits]

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@@ -87,6 +87,7 @@ define void @v_shuffle_v3i64_v4i64__1_u_u(ptr addrspace(1) inreg %ptr) {
 ; GFX942-NEXT:    ;;#ASMSTART
 ; GFX942-NEXT:    ; def v[0:7]
 ; GFX942-NEXT:    ;;#ASMEND
+; GFX942-NEXT:    global_store_dwordx2 v8, v[0:1], s[0:1] offset:16
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JanekvO wrote:

Have been looking into this, seems like legalization has opaqued the undef elements so dagcombine can't reach. Working on a patch that propagates build_vector undef elements through bitcast for extract_vector_elt.

https://github.com/llvm/llvm-project/pull/145052