[llvm] DAG: Fix vector_shuffle -> splat fold defining undef lanes (PR #123596)

[Simon Pilgrim via llvm-commits]

================
@@ -141,8 +141,10 @@ define <3 x i1> @test_urem_vec(<3 x i11> %X) nounwind {
 ; SSE2-NEXT:    pmuludq %xmm1, %xmm0
 ; SSE2-NEXT:    pshufd {{.*#+}} xmm2 = xmm0[0,2,2,3]
 ; SSE2-NEXT:    pshufd {{.*#+}} xmm1 = xmm1[1,1,1,1]
-; SSE2-NEXT:    pmuludq {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm1
-; SSE2-NEXT:    pshufd {{.*#+}} xmm1 = xmm1[0,2,2,3]
+; SSE2-NEXT:    movl $1463, %eax # imm = 0x5B7
+; SSE2-NEXT:    movd %eax, %xmm3
+; SSE2-NEXT:    pmuludq %xmm1, %xmm3
+; SSE2-NEXT:    pshufd {{.*#+}} xmm1 = xmm3[0,2,2,3]
----------------
RKSimon wrote:

not so worried about this - these already turn up quite often

https://github.com/llvm/llvm-project/pull/123596