[Clang][Sema] Process warnings conditionally

[chestnykh]

There are a few functions that emit warnings related to positional arguments in format strings. These functions use getLocationOfByte() which has O(n) complexity and may lead to silent hang of compilation in some cases. But such warnings is not widely used and actually don't emit if user didn't pass the appropriate -W... flag, so if the flag is not passed dont make the call to EmitFormatDiagnostic for such diags.

Fix #120462

[llvmbot]

@llvm/pr-subscribers-clang

Author: Dmitry Chestnykh (chestnykh)

Changes

There are a few functions that emit warnings related to positional arguments in format strings. These functions use getLocationOfByte() which has O(n) complexity and may lead to silent hang of compilation in some cases. But such warnings is not widely used and actually don't emit if user didn't pass the appropriate -W... flag, so if the flag is not passed dont make the call to EmitFormatDiagnostic for such diags.

Fix #120462

---

Full diff: https://github.com/llvm/llvm-project/pull/120591.diff

1 Files Affected:

• (modified) clang/lib/Sema/SemaChecking.cpp (+18-12)

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index be5d3694aec152..a745250988feeb 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -6612,27 +6612,33 @@ void CheckFormatHandler::HandleNonStandardConversionSpecifier(
 
 void CheckFormatHandler::HandlePosition(const char *startPos,
                                         unsigned posLen) {
-  EmitFormatDiagnostic(S.PDiag(diag::warn_format_non_standard_positional_arg),
-                               getLocationOfByte(startPos),
-                               /*IsStringLocation*/true,
-                               getSpecifierRange(startPos, posLen));
+  if (!S.getDiagnostics().isIgnored(diag::warn_format_non_standard_positional_arg, SourceLocation())) {
+    EmitFormatDiagnostic(S.PDiag(diag::warn_format_non_standard_positional_arg),
+                                getLocationOfByte(startPos),
+                                /*IsStringLocation*/true,
+                                getSpecifierRange(startPos, posLen));
+  }
 }
 
 void CheckFormatHandler::HandleInvalidPosition(
     const char *startSpecifier, unsigned specifierLen,
     analyze_format_string::PositionContext p) {
-  EmitFormatDiagnostic(
-      S.PDiag(diag::warn_format_invalid_positional_specifier) << (unsigned)p,
-      getLocationOfByte(startSpecifier), /*IsStringLocation*/ true,
-      getSpecifierRange(startSpecifier, specifierLen));
+  if (!S.getDiagnostics().isIgnored(diag::warn_format_invalid_positional_specifier, SourceLocation())) {
+    EmitFormatDiagnostic(
+        S.PDiag(diag::warn_format_invalid_positional_specifier) << (unsigned)p,
+        getLocationOfByte(startSpecifier), /*IsStringLocation*/ true,
+        getSpecifierRange(startSpecifier, specifierLen));
+  }
 }
 
 void CheckFormatHandler::HandleZeroPosition(const char *startPos,
                                             unsigned posLen) {
-  EmitFormatDiagnostic(S.PDiag(diag::warn_format_zero_positional_specifier),
-                               getLocationOfByte(startPos),
-                               /*IsStringLocation*/true,
-                               getSpecifierRange(startPos, posLen));
+  if (!S.getDiagnostics().isIgnored(diag::warn_format_zero_positional_specifier, SourceLocation())) {
+    EmitFormatDiagnostic(S.PDiag(diag::warn_format_zero_positional_specifier),
+                                getLocationOfByte(startPos),
+                                /*IsStringLocation*/true,
+                                getSpecifierRange(startPos, posLen));
+  }
 }
 
 void CheckFormatHandler::HandleNullChar(const char *nullCharacter) {

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[cor3ntin]

We do not use braces for if statements with a single child statement
LGTM otherwise

[cor3ntin]

Thanks!