[Attributor] Don't replace AddrSpaceCast with ConstantPointerNull

`ConstantPointerNull` represents a pointer with value 0, but it doesn’t
necessarily mean a nullptr. `ptr addrspace(x) null` is not the same as
`addrspacecast (ptr null to ptr addrspace(x))` if the nullptr in AS x is not
zero. Therefore, we can't simply replace it.

Fixes #115083.

Author: shiltian

llvm/lib/Transforms/IPO/Attributor.cpp

@@ -325,7 +325,7 @@ Value *AA::getWithType(Value &V, Type &Ty) {
   if (isa<UndefValue>(V))
     return UndefValue::get(&Ty);
   if (auto *C = dyn_cast<Constant>(&V)) {
-    if (C->isNullValue())
+    if (C->isNullValue() && !Ty.isPointerTy())
       return Constant::getNullValue(&Ty);
     if (C->getType()->isPointerTy() && Ty.isPointerTy())
       return ConstantExpr::getPointerCast(C, &Ty);

llvm/test/CodeGen/AMDGPU/addrspacecast.ll

@@ -217,7 +217,7 @@ define amdgpu_kernel void @use_flat_to_constant_addrspacecast(ptr %ptr) #0 {
 ; HSA-LABEL: {{^}}cast_0_group_to_flat_addrspacecast:
 
 ; HSA-DAG: v_mov_b32_e32 v[[LO:[0-9]+]], 0{{$}}
-; HSA-DAG: v_mov_b32_e32 v[[HI:[0-9]+]], 0{{$}}
+; HSA-DAG: v_mov_b32_e32 v[[HI:[0-9]+]], s{{[0-9]+}}
 ; HSA-DAG: v_mov_b32_e32 v[[K:[0-9]+]], 7{{$}}
 ; HSA: flat_store_dword v[[[LO]]:[[HI]]], v[[K]]
 define amdgpu_kernel void @cast_0_group_to_flat_addrspacecast() #0 {
@@ -260,7 +260,7 @@ define amdgpu_kernel void @cast_neg1_flat_to_group_addrspacecast() #0 {
 ; FIXME: Shouldn't need to enable queue ptr
 ; HSA-LABEL: {{^}}cast_0_private_to_flat_addrspacecast:
 ; HSA-DAG: v_mov_b32_e32 v[[LO:[0-9]+]], 0{{$}}
-; HSA-DAG: v_mov_b32_e32 v[[HI:[0-9]+]], 0{{$}}
+; HSA-DAG: v_mov_b32_e32 v[[HI:[0-9]+]], s{{[0-9]+}}
 ; HSA-DAG: v_mov_b32_e32 v[[K:[0-9]+]], 7{{$}}
 ; HSA: flat_store_dword v[[[LO]]:[[HI]]], v[[K]]
 define amdgpu_kernel void @cast_0_private_to_flat_addrspacecast() #0 {

llvm/test/Transforms/Attributor/do-not-replace-addrspacecast-with-constantpointernull.ll

@@ -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
+}