[llvm] [Attributor] Don't replace `addrspacecast (ptr null to ptr addrspace(x))` with `ptr addrspace(x) null` (PR #126779)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,34 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=attributor %s -o - | FileCheck %s
+
+define i32 @bar(ptr %p0, ptr addrspace(5) %p5) {
+; CHECK-LABEL: define i32 @bar(
+; CHECK-SAME: ptr nofree readonly captures(none) [[P0:%.*]], ptr addrspace(5) nofree readonly [[P5:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    [[ICMP:%.*]] = icmp eq ptr addrspace(5) [[P5]], addrspacecast (ptr null to ptr addrspace(5))
+; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[ICMP]], ptr [[P0]], ptr null
+; CHECK-NEXT:    [[LOAD:%.*]] = load i32, ptr [[SELECT]], align 4
+; CHECK-NEXT:    ret i32 [[LOAD]]
+;
+  %icmp = icmp eq ptr addrspace(5) %p5, addrspacecast (ptr null to ptr addrspace(5))
+  %select = select i1 %icmp, ptr %p0, ptr null
+  %load = load i32, ptr %select, align 4
+  ret i32 %load
+}
+
+define i32 @foo(ptr %p0, ptr %p1, <2 x ptr addrspace(5)> %ptrvec) {
+; CHECK-LABEL: define i32 @foo(
+; CHECK-SAME: ptr nofree readonly captures(none) [[P0:%.*]], ptr nofree noundef nonnull readonly align 16 captures(none) dereferenceable(16) [[P1:%.*]], <2 x ptr addrspace(5)> [[PTRVEC:%.*]]) #[[ATTR0]] {
+; CHECK-NEXT:    [[LOADVEC:%.*]] = load <2 x ptr addrspace(5)>, ptr [[P1]], align 16
+; CHECK-NEXT:    [[ICMPVEC:%.*]] = icmp eq <2 x ptr addrspace(5)> [[LOADVEC]], <ptr addrspace(5) addrspacecast (ptr null to ptr addrspace(5)), ptr addrspace(5) addrspacecast (ptr null to ptr addrspace(5))>
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arsenm wrote:

I'm surprised this didn't fold to a a vector `addrspacecast (<2 x ptr> zeroinitializer) to <2 x ptr addrspace(5)>`, can you check this form too 

https://github.com/llvm/llvm-project/pull/126779