[AMDGPU] Consider FLAT instructions for VMEM hazard detection

In general, "Flat instructions look at the per-workitem address and
determine for each work item if the target memory address is in global,
private or scratch memory." (RDNA2 ISA) That means that FLAT
instructions need to be considered for VMEM hazards even without
"specific segment". It should not be needed for DMA VMEM/FLAT
instructions, though.

Author: ro-i

llvm/lib/Target/AMDGPU/GCNHazardRecognizer.cpp

@@ -1424,9 +1424,9 @@ static bool shouldRunLdsBranchVmemWARHazardFixup(const MachineFunction &MF,
   bool HasVmem = false;
   for (auto &MBB : MF) {
     for (auto &MI : MBB) {
-      HasLds |= SIInstrInfo::isDS(MI);
-      HasVmem |=
-          SIInstrInfo::isVMEM(MI) || SIInstrInfo::isSegmentSpecificFLAT(MI);
+      HasLds |= SIInstrInfo::isDS(MI) || SIInstrInfo::isLDSDMA(MI);
+      HasVmem |= (SIInstrInfo::isVMEM(MI) || SIInstrInfo::isFLAT(MI)) &&
+                 !SIInstrInfo::isLDSDMA(MI);
       if (HasLds && HasVmem)
         return true;
     }
@@ -1448,9 +1448,10 @@ bool GCNHazardRecognizer::fixLdsBranchVmemWARHazard(MachineInstr *MI) {
   assert(!ST.hasExtendedWaitCounts());
 
   auto IsHazardInst = [](const MachineInstr &MI) {
-    if (SIInstrInfo::isDS(MI))
+    if (SIInstrInfo::isDS(MI) || SIInstrInfo::isLDSDMA(MI))
       return 1;
-    if (SIInstrInfo::isVMEM(MI) || SIInstrInfo::isSegmentSpecificFLAT(MI))
+    if ((SIInstrInfo::isVMEM(MI) || SIInstrInfo::isFLAT(MI)) &&
+        !SIInstrInfo::isLDSDMA(MI))
       return 2;
     return 0;
   };

llvm/test/CodeGen/AMDGPU/lds-branch-vmem-hazard.mir

@@ -269,11 +269,15 @@ body:            |
     S_ENDPGM 0
 ...
 
-# GCN-LABEL: name: no_hazard_lds_branch_flat
+# FLAT_* instructions "look at the per-workitem address and determine for each
+# work item if the target memory address is in global, private or scratch
+# memory" (RDNA2 ISA)
+# GCN-LABEL: name: hazard_lds_branch_flat
 # GCN:      bb.1:
+# GFX10-NEXT: S_WAITCNT_VSCNT undef $sgpr_null, 0
 # GCN-NEXT: FLAT_LOAD_DWORD
 ---
-name:            no_hazard_lds_branch_flat
+name:            hazard_lds_branch_flat
 body:            |
   bb.0:
     successors: %bb.1