[llvm] [AMDGPU] Implement getAddrSpaceCastPreservedPtrMask (PR #182658)

[via llvm-commits]

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@@ -207,6 +207,30 @@ class GCNTTIImpl final : public BasicTTIImplBase<GCNTTIImpl> {
     return AMDGPUAS::FLAT_ADDRESS;
   }
 
+  APInt getAddrSpaceCastPreservedPtrMask(unsigned SrcAS,
+                                         unsigned DstAS) const override {
+    // Only handle casts from flat (generic) address space.
+    if (SrcAS != AMDGPUAS::FLAT_ADDRESS)
+      return BaseT::getAddrSpaceCastPreservedPtrMask(SrcAS, DstAS);
+
+    unsigned FlatPtrSize = DL.getPointerSizeInBits(AMDGPUAS::FLAT_ADDRESS);
+
+    // For global, addresses in flat and global address spaces are the same -
+    // no conversion is needed. Global memory regions are architecturally
+    // separate from the private/local aperture regions (which are 2^32-aligned
+    // and use specific high-address ranges), so all 64 bits are preserved.
+    if (DstAS == AMDGPUAS::GLOBAL_ADDRESS)
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addmisol wrote:

Yeah sure, will add these 
Also confirmed in the [doc](https://llvm.org/docs/AMDGPUUsage.html)

https://github.com/llvm/llvm-project/pull/182658