[llvm] [Attributor] Don't replace `AddrSpaceCast` with `ConstantPointerNull` (PR #126779)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,18 @@
+; 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:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp eq ptr addrspace(5) [[P5]], addrspacecast (ptr null to ptr addrspace(5))
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[TMP0]], ptr [[P0]], ptr null
+; CHECK-NEXT:    [[TMP2:%.*]] = load i32, ptr [[TMP1]], align 4
+; CHECK-NEXT:    ret i32 [[TMP2]]
+;
+entry:
+  %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
+}
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arsenm wrote:

Also add another test with a differently typed null 

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