[AArch64][SME] Disable GlobalISel/FastISel for SME functions.

This patch ensures that GlobalISel and FastISel fall back to regular DAG ISel when:
* A function requires streaming-mode to be enabled at the start/end of the function.
  This happens when the function has no streaming interface, but does have a streaming body.
* A function requires a lazy-save to be committed at the start of the function.
  This happens if the function has the `aarch64_pstate_za_new` attribute.
* A call to a function requires a change in streaming-mode.
* A call to a function requires a lazy-save buffer to be set up.

Patch by @CarolineConcatto

Reviewed By: david-arm

Differential Revision: https://reviews.llvm.org/D136361

Author: sdesmalen-arm

llvm/lib/Target/AArch64/AArch64FastISel.cpp

@@ -5032,6 +5032,8 @@ bool AArch64FastISel::selectAtomicCmpXchg(const AtomicCmpXchgInst *I) {
 }
 
 bool AArch64FastISel::fastSelectInstruction(const Instruction *I) {
+  if (TLI.fallBackToDAGISel(*I))
+    return false;
   switch (I->getOpcode()) {
   default:
     break;
@@ -5114,5 +5116,10 @@ bool AArch64FastISel::fastSelectInstruction(const Instruction *I) {
 
 FastISel *AArch64::createFastISel(FunctionLoweringInfo &FuncInfo,
                                         const TargetLibraryInfo *LibInfo) {
+
+  SMEAttrs CallerAttrs(*FuncInfo.Fn);
+  if (CallerAttrs.hasZAState() ||
+      (!CallerAttrs.hasStreamingInterface() && CallerAttrs.hasStreamingBody()))
+    return nullptr;
   return new AArch64FastISel(FuncInfo, LibInfo);
 }

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -22054,6 +22054,15 @@ bool AArch64TargetLowering::fallBackToDAGISel(const Instruction &Inst) const {
       return true;
   }
 
+  // Checks to allow the use of SME instructions
+  if (auto *Base = dyn_cast<CallBase>(&Inst)) {
+    auto CallerAttrs = SMEAttrs(*Inst.getFunction());
+    auto CalleeAttrs = SMEAttrs(*Base);
+    if (CallerAttrs.requiresSMChange(CalleeAttrs,
+                                     /*BodyOverridesInterface=*/false) ||
+        CallerAttrs.requiresLazySave(CalleeAttrs))
+      return true;
+  }
   return false;
 }
 

llvm/lib/Target/AArch64/GISel/AArch64CallLowering.cpp

@@ -537,6 +537,12 @@ bool AArch64CallLowering::fallBackToDAGISel(const MachineFunction &MF) const {
     LLVM_DEBUG(dbgs() << "Falling back to SDAG because we don't support no-NEON\n");
     return true;
   }
+
+  SMEAttrs Attrs(F);
+  if (Attrs.hasNewZAInterface() ||
+      (!Attrs.hasStreamingInterface() && Attrs.hasStreamingBody()))
+    return true;
+
   return false;
 }