AMDGPU/GlobalISel: Legalize atomicrmw fmin/fmax

We only handled the easy LDS case before. Handle the other address spaces
with the more complicated legality logic.

Author: arsenm

llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp

@@ -1670,10 +1670,22 @@ AMDGPULegalizerInfo::AMDGPULegalizerInfo(const GCNSubtarget &ST_,
   if (ST.hasAtomicFlatPkAdd16Insts())
     Atomic.legalFor({{V2F16, FlatPtr}, {V2BF16, FlatPtr}});
 
-  // FIXME: Handle flat, global and buffer cases.
-  getActionDefinitionsBuilder({G_ATOMICRMW_FMIN, G_ATOMICRMW_FMAX})
+
+  // Most of the legalization work here is done by AtomicExpand. We could
+  // probably use a simpler legality rule that just assumes anything is OK.
+  auto &AtomicFMinFMax =
+    getActionDefinitionsBuilder({G_ATOMICRMW_FMIN, G_ATOMICRMW_FMAX})
     .legalFor({{F32, LocalPtr}, {F64, LocalPtr}});
 
+  if (ST.hasAtomicFMinFMaxF32GlobalInsts())
+    AtomicFMinFMax.legalFor({{F32, GlobalPtr},{F32, BufferFatPtr}});
+  if (ST.hasAtomicFMinFMaxF64GlobalInsts())
+    AtomicFMinFMax.legalFor({{F64, GlobalPtr}, {F64, BufferFatPtr}});
+  if (ST.hasAtomicFMinFMaxF32FlatInsts())
+    AtomicFMinFMax.legalFor({F32, FlatPtr});
+  if (ST.hasAtomicFMinFMaxF64FlatInsts())
+    AtomicFMinFMax.legalFor({F64, FlatPtr});
+
   // BUFFER/FLAT_ATOMIC_CMP_SWAP on GCN GPUs needs input marshalling, and output
   // demarshalling
   getActionDefinitionsBuilder(G_ATOMIC_CMPXCHG)