[llvm] [SROA] Unfold gep of index select (PR #80983)

[Arthur Eubanks via llvm-commits]

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@@ -158,11 +158,20 @@ bb:
 
 define i32 @test_select_idx_memcpy(i1 %c, ptr %p) {
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aeubanks wrote:

the two large memcpys and their corresponding allocas are now dead and will be removed later

https://github.com/llvm/llvm-project/pull/80983