[clang] [clang][AArch64] Avoid a crash when a non-reserved register is used (PR #117419)

[Daniel Kiss via cfe-commits]

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@@ -232,13 +232,23 @@ bool AArch64TargetInfo::validateTarget(DiagnosticsEngine &Diags) const {
 
 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")) {
+  if (RegName.starts_with("w")) {
     HasSizeMismatch = RegSize != 32;
     return true;
   }
+  if (RegName == "sp") {
+    HasSizeMismatch = RegSize != 64;
+    return true;
+  }
+  if (RegName.starts_with("x")) {
+    HasSizeMismatch = RegSize != 64;
+    // Check if the register is reserved. See also
+    // AArch64TargetLowering::getRegisterByName().
+    return RegName == "x0" ||
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DanielKristofKiss wrote:

maybe add a test case for x0 too?

https://github.com/llvm/llvm-project/pull/117419