[clang] [Clang][Sema] Process warnings conditionally (PR #120591)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Dmitry Chestnykh (chestnykh)

<details>
<summary>Changes</summary>

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
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) {

``````````

</details>


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