Reland "[lldb][AArch64] Invalidate SVG prior to reconfiguring ZA regdef (#66768)""

This reverts commit 8d80a45.

The pointer to the invalidates lists needs to be non-const. Though in this case
I don't think it's ever modified.

Also I realised that the invalidate list was being set on svg not vg.
Should be the other way around.

Author: DavidSpickett

lldb/source/Plugins/Process/Utility/RegisterInfoPOSIX_arm64.cpp

@@ -374,6 +374,17 @@ void RegisterInfoPOSIX_arm64::AddRegSetSME() {
       std::make_pair(sme_regnum, m_dynamic_reg_infos.size());
   m_dynamic_reg_sets.push_back(g_reg_set_sme_arm64);
   m_dynamic_reg_sets.back().registers = m_sme_regnum_collection.data();
+
+  // When vg is written during streaming mode, svg will also change, as vg and
+  // svg in this state are both showing the streaming vector length.
+  // We model this as vg invalidating svg. In non-streaming mode this doesn't
+  // happen but to keep things simple we will invalidate svg anyway.
+  //
+  // This must be added now, rather than when vg is defined because SME is a
+  // dynamic set that may or may not be present.
+  static uint32_t vg_invalidates[] = {sme_regnum + 1 /*svg*/,
+                                      LLDB_INVALID_REGNUM};
+  m_dynamic_reg_infos[GetRegNumSVEVG()].invalidate_regs = vg_invalidates;
 }
 
 uint32_t RegisterInfoPOSIX_arm64::ConfigureVectorLengthSVE(uint32_t sve_vq) {

lldb/source/Plugins/Process/gdb-remote/GDBRemoteRegisterContext.cpp

@@ -783,6 +783,11 @@ void GDBRemoteRegisterContext::AArch64Reconfigure() {
   std::optional<uint64_t> svg_reg_value;
   const RegisterInfo *svg_reg_info = m_reg_info_sp->GetRegisterInfo("svg");
   if (svg_reg_info) {
+    // When vg is written it is automatically made invalid. Writing vg will also
+    // change svg if we're in streaming mode but it will not be made invalid
+    // so do this manually so the following read gets the latest svg value.
+    SetRegisterIsValid(svg_reg_info, false);
+
     uint32_t svg_reg_num = svg_reg_info->kinds[eRegisterKindLLDB];
     uint64_t reg_value = ReadRegisterAsUnsigned(svg_reg_num, fail_value);
     if (reg_value != fail_value && reg_value <= 32)

lldb/test/API/commands/register/register/aarch64_za_register/za_dynamic_resize/TestZAThreadedDynamic.py

@@ -125,11 +125,13 @@ def za_test_impl(self, enable_za):
                 self.runCmd("thread select %d" % (idx + 1))
                 self.check_za_register(4, 2)
                 self.runCmd("register write vg 2")
+                self.check_disabled_za_register(2)
 
             elif stopped_at_line_number == thY_break_line1:
                 self.runCmd("thread select %d" % (idx + 1))
                 self.check_za_register(2, 3)
                 self.runCmd("register write vg 4")
+                self.check_disabled_za_register(4)
 
         self.runCmd("thread continue 2")
         self.runCmd("thread continue 3")