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

Relanding the patch with a fix for a test failure on build bots that do
not build LLVM for AArch64.

Fixes #76426, #109778 (for AArch64)

The previous patch for this issue, #94271, generated an error message if
a register and a global variable did not have the same size. This patch
checks if the register is reserved.

Author: igorkudrin

clang/lib/Basic/Targets/AArch64.cpp

@@ -232,14 +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")) {
+  if (RegName == "sp") {
     HasSizeMismatch = RegSize != 64;
     return true;
-  } else if (RegName.starts_with("w")) {
-    HasSizeMismatch = RegSize != 32;
-    return true;
   }
-  return false;
+  if (RegName.starts_with("w"))
+    HasSizeMismatch = RegSize != 32;
+  else if (RegName.starts_with("x"))
+    HasSizeMismatch = RegSize != 64;
+  else
+    return false;
+  StringRef RegNum = RegName.drop_front();
+  // Check if the register is reserved. See also
+  // AArch64TargetLowering::getRegisterByName().
+  return RegNum == "0" ||
+         (RegNum == "18" &&
+          llvm::AArch64::isX18ReservedByDefault(getTriple())) ||
+         getTargetOpts().FeatureMap.lookup(("reserve-x" + RegNum).str());
 }
 
 bool AArch64TargetInfo::validateBranchProtection(StringRef Spec, StringRef,

clang/test/CodeGen/AArch64/fixed-register-global.c

@@ -0,0 +1,23 @@
+/// Check that -ffixed register handled for globals.
+/// Regression test for #76426, #109778
+// REQUIRES: aarch64-registered-target
+
+// RUN: %clang -c --target=aarch64-none-gnu -ffixed-x15 %s 2>&1 | count 0
+
+// RUN: not %clang -c --target=aarch64-none-gnu %s 2>&1 | \
+// RUN:   FileCheck %s --check-prefix=ERR_INVREG
+// ERR_INVREG: error: register 'x15' unsuitable for global register variables on this target
+
+// RUN: not %clang -c --target=aarch64-none-gnu -ffixed-x15 -DTYPE=short %s 2>&1 | \
+// RUN:   FileCheck %s --check-prefix=ERR_SIZE
+// ERR_SIZE: error: size of register 'x15' does not match variable size
+
+#ifndef TYPE
+#define TYPE long
+#endif
+
+register TYPE x15 __asm__("x15");
+
+TYPE foo() {
+  return x15;
+}

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

@@ -1,4 +1,13 @@
-// RUN: %clang_cc1 -triple aarch64-unknown-none-gnu %s -verify -fsyntax-only
+// RUN: %clang_cc1 -triple aarch64-unknown-none-gnu %s -target-feature +reserve-x4 -target-feature +reserve-x15 -verify -verify=no_x18 -fsyntax-only
+// RUN: %clang_cc1 -triple aarch64-unknown-android %s -target-feature +reserve-x4 -target-feature +reserve-x15 -verify -fsyntax-only
 
+register int w0 __asm__ ("w0");
+register long x0 __asm__ ("x0");
 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}}
+register long long l2 __asm__ ("w15"); // expected-error {{size of register 'w15' does not match variable size}}
+register int w3 __asm__ ("w3"); // expected-error {{register 'w3' unsuitable for global register variables on this target}}
+register long x3 __asm__ ("x3"); // expected-error {{register 'x3' unsuitable for global register variables on this target}}
+register int w4 __asm__ ("w4");
+register long x4 __asm__ ("x4");
+register int w18 __asm__ ("w18"); // no_x18-error {{register 'w18' unsuitable for global register variables on this target}}
+register long x18 __asm__ ("x18"); // no_x18-error {{register 'x18' unsuitable for global register variables on this target}}