AMDGPU: Expand remaining system atomic operations (llvm#122137)

System scope atomics need to use cmpxchg loops if we know
nothing about the allocation the address is from.
aea5980 started this, this
expands the set to cover the remaining integer operations.

Don't expand xchg and add, those theoretically should work over PCIe.
This is a pre-commit which will introduce performance regressions.
Subsequent changes will add handling of new atomicrmw metadata, which
will avoid the expansion.

Note this still isn't conservative enough; we do need to expand
some device scope atomics if the memory is in fine-grained remote
memory.

Author: arsenm

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -17840,26 +17840,39 @@ SITargetLowering::shouldExpandAtomicRMWInIR(AtomicRMWInst *RMW) const {
 
   auto Op = RMW->getOperation();
   switch (Op) {
-  case AtomicRMWInst::Xchg: {
+  case AtomicRMWInst::Xchg:
     // PCIe supports add and xchg for system atomics.
     return isAtomicRMWLegalXChgTy(RMW)
                ? TargetLowering::AtomicExpansionKind::None
                : TargetLowering::AtomicExpansionKind::CmpXChg;
-  }
   case AtomicRMWInst::Add:
-  case AtomicRMWInst::And:
-  case AtomicRMWInst::UIncWrap:
-  case AtomicRMWInst::UDecWrap:
+    // PCIe supports add and xchg for system atomics.
     return atomicSupportedIfLegalIntType(RMW);
   case AtomicRMWInst::Sub:
+  case AtomicRMWInst::And:
   case AtomicRMWInst::Or:
-  case AtomicRMWInst::Xor: {
-    // Atomic sub/or/xor do not work over PCI express, but atomic add
-    // does. InstCombine transforms these with 0 to or, so undo that.
-    if (HasSystemScope && AMDGPU::isFlatGlobalAddrSpace(AS)) {
-      if (Constant *ConstVal = dyn_cast<Constant>(RMW->getValOperand());
-          ConstVal && ConstVal->isNullValue())
-        return AtomicExpansionKind::Expand;
+  case AtomicRMWInst::Xor:
+  case AtomicRMWInst::Max:
+  case AtomicRMWInst::Min:
+  case AtomicRMWInst::UMax:
+  case AtomicRMWInst::UMin:
+  case AtomicRMWInst::UIncWrap:
+  case AtomicRMWInst::UDecWrap: {
+    if (AMDGPU::isFlatGlobalAddrSpace(AS) ||
+        AS == AMDGPUAS::BUFFER_FAT_POINTER) {
+      // Always expand system scope atomics.
+      if (HasSystemScope && !Subtarget->hasEmulatedSystemScopeAtomics()) {
+        if (Op == AtomicRMWInst::Sub || Op == AtomicRMWInst::Or ||
+            Op == AtomicRMWInst::Xor) {
+          // Atomic sub/or/xor do not work over PCI express, but atomic add
+          // does. InstCombine transforms these with 0 to or, so undo that.
+          if (Constant *ConstVal = dyn_cast<Constant>(RMW->getValOperand());
+              ConstVal && ConstVal->isNullValue())
+            return AtomicExpansionKind::Expand;
+        }
+
+        return AtomicExpansionKind::CmpXChg;
+      }
     }
 
     return atomicSupportedIfLegalIntType(RMW);
@@ -18014,18 +18027,6 @@ SITargetLowering::shouldExpandAtomicRMWInIR(AtomicRMWInst *RMW) const {
 
     return AtomicExpansionKind::CmpXChg;
   }
-  case AtomicRMWInst::Min:
-  case AtomicRMWInst::Max:
-  case AtomicRMWInst::UMin:
-  case AtomicRMWInst::UMax: {
-    if (AMDGPU::isFlatGlobalAddrSpace(AS) ||
-        AS == AMDGPUAS::BUFFER_FAT_POINTER) {
-      if (HasSystemScope && !Subtarget->hasEmulatedSystemScopeAtomics())
-        return AtomicExpansionKind::CmpXChg;
-    }
-
-    return atomicSupportedIfLegalIntType(RMW);
-  }
   case AtomicRMWInst::Nand:
   case AtomicRMWInst::FSub:
   default: