[clang] Increase the default expression nesting limit (#104717)

Increase the default expression nesting limit from 256 to 1024

Fixes: #94728

Compile time with different Bracket depth

Clang version 20.0.0git
(https://github.com/AmrDeveloper/llvm-project.git
673b9e0)
Target: arm64-apple-darwin23.5.0

Bracket depth = 256, time = 0.243
Bracket depth = 512, time = 0.329
Bracket depth = 1024, time = 0.489
Bracket depth = 2048, time = 0.851

Author: AmrDeveloper

clang/docs/ReleaseNotes.rst

@@ -174,6 +174,8 @@ Deprecated Compiler Flags
 Modified Compiler Flags
 -----------------------
 
+- The compiler flag `-fbracket-depth` default value is increased from 256 to 2048.
+
 Removed Compiler Flags
 -------------------------
 

clang/include/clang/Driver/Options.td

@@ -7959,7 +7959,7 @@ def fapply_global_visibility_to_externs : Flag<["-"], "fapply-global-visibility-
   MarshallingInfoFlag<LangOpts<"SetVisibilityForExternDecls">>;
 def fbracket_depth : Separate<["-"], "fbracket-depth">,
   HelpText<"Maximum nesting level for parentheses, brackets, and braces">,
-  MarshallingInfoInt<LangOpts<"BracketDepth">, "256">;
+  MarshallingInfoInt<LangOpts<"BracketDepth">, "2048">;
 defm const_strings : BoolOption<"f", "const-strings",
   LangOpts<"ConstStrings">, DefaultFalse,
   PosFlag<SetTrue, [], [ClangOption, CC1Option], "Use">,

clang/test/Parser/parser_overflow.c

@@ -1,5 +1,5 @@
 // RUN: not %clang_cc1 %s -fsyntax-only -DHUGE 2>&1 | FileCheck %s
-// RUN: not %clang_cc1 %s -fsyntax-only 2>&1 | FileCheck %s
+// RUN: %clang_cc1 %s -fsyntax-only
 // RUN: not %clang_cc1 %s -fsyntax-only -fbracket-depth 299 2>&1 | FileCheck %s
 // RUN: %clang_cc1 %s -fsyntax-only -fbracket-depth 300
 // RUN: not %clang %s -fsyntax-only -fbracket-depth=299 2>&1 | FileCheck %s
@@ -15,5 +15,5 @@ void foo(void) {
 #endif
 }
 
-// CHECK: fatal error: bracket nesting level exceeded maximum of {{256|299}}
+// CHECK: fatal error: bracket nesting level exceeded maximum of {{2048|299}}
 // CHECK: note: use -fbracket-depth=N to increase maximum nesting level