[llvm] [AMDGPU] Allow casts between the Global and Constant Addr Spaces in isValidAddrSpaceCast (PR #112493)

[Matt Arsenault via llvm-commits]

================
@@ -174,24 +174,45 @@ class GCNTTIImpl final : public BasicTTIImplBase<GCNTTIImpl> {
   bool isAlwaysUniform(const Value *V) const;
 
   bool isValidAddrSpaceCast(unsigned FromAS, unsigned ToAS) const {
-    if (ToAS == AMDGPUAS::FLAT_ADDRESS) {
-      switch (FromAS) {
+    // Address space casts must cast between different address spaces.
+    if (FromAS == ToAS)
+      return false;
+
+    if (FromAS == AMDGPUAS::FLAT_ADDRESS ||
+        FromAS == AMDGPUAS::GLOBAL_ADDRESS ||
+        FromAS == AMDGPUAS::CONSTANT_ADDRESS ||
+        FromAS > AMDGPUAS::MAX_AMDGPU_ADDRESS) {
----------------
arsenm wrote:

Use AMDGPU::isFlatGlobalAddrSpace instead of repeating it 

https://github.com/llvm/llvm-project/pull/112493