[AArch64] Add validation for Global Register Variable.

Fixes: #76426

Author: DanielKristofKiss

clang/lib/Basic/Targets/AArch64.cpp

@@ -221,6 +221,18 @@ bool AArch64TargetInfo::validateTarget(DiagnosticsEngine &Diags) const {
   return true;
 }
 
+bool AArch64TargetInfo::validateGlobalRegisterVariable(
+    StringRef RegName, unsigned RegSize, bool &HasSizeMismatch) const {
+  if ((RegName == "sp") || RegName.starts_with("x")) {
+    HasSizeMismatch = RegSize != 64;
+    return true;
+  } else if (RegName.starts_with("w")) {
+    HasSizeMismatch = RegSize != 32;
+    return true;
+  }
+  return false;
+}
+
 bool AArch64TargetInfo::validateBranchProtection(StringRef Spec, StringRef,
                                                  BranchProtectionInfo &BPI,
                                                  StringRef &Err) const {

clang/lib/Basic/Targets/AArch64.h

@@ -202,6 +202,9 @@ class LLVM_LIBRARY_VISIBILITY AArch64TargetInfo : public TargetInfo {
   bool hasBitIntType() const override { return true; }
 
   bool validateTarget(DiagnosticsEngine &Diags) const override;
+
+  bool validateGlobalRegisterVariable(StringRef RegName, unsigned RegSize,
+                                      bool &HasSizeMismatch) const override;
 };
 
 class LLVM_LIBRARY_VISIBILITY AArch64leTargetInfo : public AArch64TargetInfo {

clang/test/Driver/aarch64-fixed-register-global.c

@@ -0,0 +1,12 @@
+// Check that -ffixed register handled for globals.
+// Regression test for #76426
+// RUN: %clang --target=aarch64-none-gnu -ffixed-x15 -### %s 2>&1 | FileCheck %s
+// CHECK-NOT: fatal error: error in backend: Invalid register name "x15".
+register int i1 __asm__("x15");
+
+int foo() {
+  return i1;
+}
+int main() {
+  return foo();
+}

clang/test/Sema/aarch64-fixed-global-register.c

@@ -0,0 +1,4 @@
+// RUN: %clang_cc1 -triple aarch64-unknown-none-gnu %s -verify -fsyntax-only
+
+register char i1 __asm__ ("x15"); // expected-error {{size of register 'x15' does not match variable size}}
+register long long l2 __asm__ ("w14"); // expected-error {{size of register 'w14' does not match variable size}}