AMDGPU: Start selecting buffer fat pointer atomicrmw fmin/fmax (#95593)

Author: arsenm

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -16104,7 +16104,8 @@ SITargetLowering::shouldExpandAtomicRMWInIR(AtomicRMWInst *RMW) const {
         return ReportUnsafeHWInst(AtomicExpansionKind::None);
       if (Subtarget->hasAtomicFMinFMaxF64FlatInsts() && Ty->isDoubleTy())
         return ReportUnsafeHWInst(AtomicExpansionKind::None);
-    } else if (AMDGPU::isExtendedGlobalAddrSpace(AS)) {
+    } else if (AMDGPU::isExtendedGlobalAddrSpace(AS) ||
+               AS == AMDGPUAS::BUFFER_FAT_POINTER) {
       if (Subtarget->hasAtomicFMinFMaxF32GlobalInsts() && Ty->isFloatTy())
         return ReportUnsafeHWInst(AtomicExpansionKind::None);
       if (Subtarget->hasAtomicFMinFMaxF64GlobalInsts() && Ty->isDoubleTy())