[AArch64][SME] Implement inline-asm clobbers for za/zt0

This enables specifing "za" or "zt0" to the clobber list
for inline asm. This complies with the acle SME addition to the
asm extension here:
ARM-software/acle#276

Author: MDevereau

clang/lib/Basic/Targets/AArch64.cpp

@@ -1200,7 +1200,10 @@ const char *const AArch64TargetInfo::GCCRegNames[] = {
 
     // SVE predicate-as-counter registers
     "pn0",  "pn1",  "pn2",  "pn3",  "pn4",  "pn5",  "pn6",  "pn7",  "pn8",
-    "pn9",  "pn10", "pn11", "pn12", "pn13", "pn14", "pn15"
+    "pn9",  "pn10", "pn11", "pn12", "pn13", "pn14", "pn15",
+
+    // SME registers
+    "za", "zt0",
 };
 
 ArrayRef<const char *> AArch64TargetInfo::getGCCRegNames() const {

clang/test/CodeGen/aarch64-inline-asm.c

@@ -95,3 +95,11 @@ void test_reduced_gpr_constraints(int var32, long var64) {
 // CHECK: [[ARG2:%.+]] = load i64, ptr
 // CHECK: call void asm sideeffect "add x0, x0, $0", "@3Ucj,~{x0}"(i64 [[ARG2]])
 }
+
+void test_sme_constraints(){
+  asm("movt zt0[3, mul vl], z0" : : : "za");
+// CHECK: call void asm sideeffect "movt zt0[3, mul vl], z0", "~{za}"()
+
+  asm("movt zt0[3, mul vl], z0" : : : "zt0");
+// CHECK: call void asm sideeffect "movt zt0[3, mul vl], z0", "~{zt0}"()
+}

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -10702,6 +10702,14 @@ AArch64TargetLowering::getRegForInlineAsmConstraint(
       parseConstraintCode(Constraint) != AArch64CC::Invalid)
     return std::make_pair(unsigned(AArch64::NZCV), &AArch64::CCRRegClass);
 
+  if (StringRef("{za}").equals_insensitive(Constraint)){
+    return std::make_pair(unsigned(AArch64::ZA), &AArch64::MPRRegClass);
+  }
+
+  if (StringRef("{zt0}").equals_insensitive(Constraint)){
+    return std::make_pair(unsigned(AArch64::ZT0), &AArch64::ZTRRegClass);
+  }
+
   // Use the default implementation in TargetLowering to convert the register
   // constraint into a member of a register class.
   std::pair<unsigned, const TargetRegisterClass *> Res;

llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp

@@ -507,6 +507,10 @@ bool AArch64RegisterInfo::isAsmClobberable(const MachineFunction &MF,
         MCRegisterInfo::regsOverlap(PhysReg, AArch64::X16))
     return true;
 
+  // ZA/ZT0 registers are reserved but may be permitted in the clobber list.
+  if (PhysReg.id() == AArch64::ZA || PhysReg.id() == AArch64::ZT0)
+    return true;
+
   return !isReservedReg(MF, PhysReg);
 }
 

llvm/test/CodeGen/AArch64/aarch64-za-clobber.ll

@@ -0,0 +1,16 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=aarch64-none-linux-gnu -stop-after=aarch64-isel < %s -o - | FileCheck %s
+
+define void @alpha(<vscale x 4 x i32> %x) local_unnamed_addr {
+entry:
+; CHECK: INLINEASM &"movt zt0[3, mul vl], z0", 1 /* sideeffect attdialect */, 12 /* clobber */, implicit-def early-clobber $za
+  tail call void asm sideeffect "movt zt0[3, mul vl], z0", "~{za}"()
+  ret void
+}
+
+define void @beta(<vscale x 4 x i32> %x) local_unnamed_addr {
+entry:
+; CHECK: INLINEASM &"movt zt0[3, mul vl], z0", 1 /* sideeffect attdialect */, 12 /* clobber */, implicit-def early-clobber $zt0
+  tail call void asm sideeffect "movt zt0[3, mul vl], z0", "~{zt0}"()
+  ret void
+}