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

This reverts commit 8fc6fca.

Author: igorkudrin

clang/lib/Basic/Targets/AArch64.cpp

@@ -232,23 +232,14 @@ bool AArch64TargetInfo::validateTarget(DiagnosticsEngine &Diags) const {
 
 bool AArch64TargetInfo::validateGlobalRegisterVariable(
     StringRef RegName, unsigned RegSize, bool &HasSizeMismatch) const {
-  if (RegName == "sp") {
+  if ((RegName == "sp") || RegName.starts_with("x")) {
     HasSizeMismatch = RegSize != 64;
     return true;
-  }
-  if (RegName.starts_with("w"))
+  } else 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());
+    return true;
+  }
+  return false;
 }
 
 bool AArch64TargetInfo::validateBranchProtection(StringRef Spec, StringRef,

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

@@ -1,13 +1,4 @@
-// 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
+// RUN: %clang_cc1 -triple aarch64-unknown-none-gnu %s -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__ ("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}}
+register long long l2 __asm__ ("w14"); // expected-error {{size of register 'w14' does not match variable size}}