[AArch64] Initial compiler support for SVE unwind on Windows. (#138609)

Most bits of this are straightforward: when we emit SVE instructions in
the prologue/epilogue, emit corresponding opcodes.

The unfortunately nasty bit is the handling of the frame pointer in
functions that use the SVE calling convention. If we have SVE callee
saves, and need to restore the stack pointer from the frame pointer,
it's impossible to encode callee saves that happen after the frame
pointer. So this patch rearranges the stack to put SVE callee saves
first. This isn't really that complicated on its own, but it leads to a
lot of tricky conditionals (see FPAfterSVECalleeSaves).

Author: efriedma-quic

llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp

@@ -3273,6 +3273,32 @@ void AArch64AsmPrinter::emitInstruction(const MachineInstr *MI) {
                                      -MI->getOperand(2).getImm());
     return;
 
+  case AArch64::SEH_AllocZ:
+    assert(MI->getOperand(0).getImm() >= 0 &&
+           "AllocZ SEH opcode offset must be non-negative");
+    assert(MI->getOperand(0).getImm() <= 255 &&
+           "AllocZ SEH opcode offset must fit into 8 bits");
+    TS->emitARM64WinCFIAllocZ(MI->getOperand(0).getImm());
+    return;
+
+  case AArch64::SEH_SaveZReg:
+    assert(MI->getOperand(1).getImm() >= 0 &&
+           "SaveZReg SEH opcode offset must be non-negative");
+    assert(MI->getOperand(1).getImm() <= 255 &&
+           "SaveZReg SEH opcode offset must fit into 8 bits");
+    TS->emitARM64WinCFISaveZReg(MI->getOperand(0).getImm(),
+                                MI->getOperand(1).getImm());
+    return;
+
+  case AArch64::SEH_SavePReg:
+    assert(MI->getOperand(1).getImm() >= 0 &&
+           "SavePReg SEH opcode offset must be non-negative");
+    assert(MI->getOperand(1).getImm() <= 255 &&
+           "SavePReg SEH opcode offset must fit into 8 bits");
+    TS->emitARM64WinCFISavePReg(MI->getOperand(0).getImm(),
+                                MI->getOperand(1).getImm());
+    return;
+
   case AArch64::BLR:
   case AArch64::BR: {
     recordIfImportCall(MI);

llvm/lib/Target/AArch64/AArch64CallingConvention.td

@@ -606,6 +606,9 @@ def CSR_Win_AArch64_Arm64EC_Thunk : CalleeSavedRegs<(add (sequence "Q%u", 6, 15)
 def CSR_AArch64_AAVPCS : CalleeSavedRegs<(add X19, X20, X21, X22, X23, X24,
                                           X25, X26, X27, X28, LR, FP,
                                           (sequence "Q%u", 8, 23))>;
+def CSR_Win_AArch64_AAVPCS : CalleeSavedRegs<(add X19, X20, X21, X22, X23, X24,
+                                              X25, X26, X27, X28, FP, LR,
+                                              (sequence "Q%u", 8, 23))>;
 
 // Functions taking SVE arguments or returning an SVE type
 // must (additionally) preserve full Z8-Z23 and predicate registers P4-P15
@@ -619,6 +622,11 @@ def CSR_Darwin_AArch64_SVE_AAPCS : CalleeSavedRegs<(add (sequence "Z%u", 8, 23),
                                                         LR, FP, X19, X20, X21, X22,
                                                         X23, X24, X25, X26, X27, X28)>;
 
+def CSR_Win_AArch64_SVE_AAPCS : CalleeSavedRegs<(add (sequence "P%u", 4, 15),
+                                                     (sequence "Z%u", 8, 23),
+                                                     X19, X20, X21, X22, X23, X24,
+                                                     X25, X26, X27, X28, FP, LR)>;
+
 // SME ABI support routines such as __arm_tpidr2_save/restore preserve most registers.
 def CSR_AArch64_SME_ABI_Support_Routines_PreserveMost_From_X0
                           : CalleeSavedRegs<(add (sequence "Z%u", 0, 31),