[clang-tidy] fix bugprone-narrowing-conversions false positive for conditional expression
#139474
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@llvm/pr-subscribers-clang-tidy @llvm/pr-subscribers-clang-tools-extra Author: Andrey (AndreyG) ChangesLet's consider the following code from the issue #139467: void test(int cond, char c) {
char ret = cond > 0 ? ':' : c;
}Initializer of So it could be seen that Full diff: https://github.com/llvm/llvm-project/pull/139474.diff 3 Files Affected:
diff --git a/clang-tools-extra/clang-tidy/bugprone/NarrowingConversionsCheck.cpp b/clang-tools-extra/clang-tidy/bugprone/NarrowingConversionsCheck.cpp
index bafcd402ca851..9e53bfe83e03e 100644
--- a/clang-tools-extra/clang-tidy/bugprone/NarrowingConversionsCheck.cpp
+++ b/clang-tools-extra/clang-tidy/bugprone/NarrowingConversionsCheck.cpp
@@ -554,15 +554,23 @@ bool NarrowingConversionsCheck::handleConditionalOperator(
// We have an expression like so: `output = cond ? lhs : rhs`
// From the point of view of narrowing conversion we treat it as two
// expressions `output = lhs` and `output = rhs`.
- handleBinaryOperator(Context, CO->getLHS()->getExprLoc(), Lhs,
- *CO->getLHS());
- handleBinaryOperator(Context, CO->getRHS()->getExprLoc(), Lhs,
- *CO->getRHS());
+ handleConditionalOperatorArgument(Context, Lhs, CO->getLHS());
+ handleConditionalOperatorArgument(Context, Lhs, CO->getRHS());
return true;
}
return false;
}
+void NarrowingConversionsCheck::handleConditionalOperatorArgument(
+ const ASTContext &Context, const Expr &Lhs, const Expr *Arg) {
+ if (const auto *ICE = llvm::dyn_cast<ImplicitCastExpr>(Arg)) {
+ if (!Arg->getIntegerConstantExpr(Context)) {
+ Arg = ICE->getSubExpr();
+ }
+ }
+ handleBinaryOperator(Context, Arg->getExprLoc(), Lhs, *Arg);
+}
+
void NarrowingConversionsCheck::handleImplicitCast(
const ASTContext &Context, const ImplicitCastExpr &Cast) {
if (Cast.getExprLoc().isMacroID())
diff --git a/clang-tools-extra/clang-tidy/bugprone/NarrowingConversionsCheck.h b/clang-tools-extra/clang-tidy/bugprone/NarrowingConversionsCheck.h
index 20403f920b925..ebddbc2869675 100644
--- a/clang-tools-extra/clang-tidy/bugprone/NarrowingConversionsCheck.h
+++ b/clang-tools-extra/clang-tidy/bugprone/NarrowingConversionsCheck.h
@@ -85,6 +85,8 @@ class NarrowingConversionsCheck : public ClangTidyCheck {
bool handleConditionalOperator(const ASTContext &Context, const Expr &Lhs,
const Expr &Rhs);
+ void handleConditionalOperatorArgument(const ASTContext &Context, const Expr &Lhs,
+ const Expr *Arg);
void handleImplicitCast(const ASTContext &Context,
const ImplicitCastExpr &Cast);
diff --git a/clang-tools-extra/test/clang-tidy/checkers/bugprone/narrowing-conversions-conditional-expressions.c b/clang-tools-extra/test/clang-tidy/checkers/bugprone/narrowing-conversions-conditional-expressions.c
new file mode 100644
index 0000000000000..754d6425b07cd
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/bugprone/narrowing-conversions-conditional-expressions.c
@@ -0,0 +1,6 @@
+// RUN: %check_clang_tidy %s bugprone-narrowing-conversions %t -- --
+
+char test(int cond, char c) {
+ char ret = cond > 0 ? ':' : c;
+ return ret;
+}
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Please mention changes in Release Notes. |
vbvictor
reviewed
May 12, 2025
Comment on lines
566
to
569
| if (const auto *ICE = llvm::dyn_cast<ImplicitCastExpr>(Arg)) { | ||
| if (!Arg->getIntegerConstantExpr(Context)) { | ||
| Arg = ICE->getSubExpr(); | ||
| } | ||
| } |
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As per LLVM coding-style, there shouldn't be any braces for single-stmt ifs.
if (const auto *ICE = llvm::dyn_cast<ImplicitCastExpr>(Arg))
if (!Arg->getIntegerConstantExpr(Context))
Arg = ICE->getSubExpr();There was a problem hiding this comment.
There was a problem hiding this comment.
Sorry, I've lost the change during rebase. Fixed this again (f350b58).
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5chmidti
changed the title
bugprone-narrowing-conversions false positive for conditional expression
5chmidti
reviewed
Jul 12, 2025
...ools-extra/test/clang-tidy/checkers/bugprone/narrowing-conversions-conditional-expressions.c
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✅ With the latest revision this PR passed the C/C++ code formatter. |
...ools-extra/test/clang-tidy/checkers/bugprone/narrowing-conversions-conditional-expressions.c
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5chmidti
approved these changes
Jul 14, 2025
Comment on lines
566
to
569
| if (const auto *ICE = llvm::dyn_cast<ImplicitCastExpr>(Arg)) { | ||
| if (!Arg->getIntegerConstantExpr(Context)) { | ||
| Arg = ICE->getSubExpr(); | ||
| } | ||
| } |
vbvictor
approved these changes
Jul 25, 2025
Let's consider the following code from the issue llvm#139467: void test(int cond, char c) { char ret = cond > 0 ? ':' : c; } Initializer of 'ret' looks the following: -ImplicitCastExpr 'char' <IntegralCast> `-ConditionalOperator 'int' |-BinaryOperator 'int' '>' | |-ImplicitCastExpr 'int' <LValueToRValue> | | `-DeclRefExpr 'int' lvalue ParmVar 'cond' 'int' | `-IntegerLiteral 'int' 0 |-CharacterLiteral 'int' 58 `-ImplicitCastExpr 'int' <IntegralCast> `-ImplicitCastExpr 'char' <LValueToRValue> `-DeclRefExpr 'char' lvalue ParmVar 'c' 'char' So it could be seen that 'RHS' of the conditional operator is DeclRefExpr 'c' which is casted to 'int' and then the whole conditional expression is casted to 'char'. But this last conversion is not narrowing, because 'RHS' was 'char' _initially_. We should just remove the cast from 'char' to 'int' before the narrowing conversion check.
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@AndreyG Congratulations on having your first Pull Request (PR) merged into the LLVM Project! Your changes will be combined with recent changes from other authors, then tested by our build bots. If there is a problem with a build, you may receive a report in an email or a comment on this PR. Please check whether problems have been caused by your change specifically, as the builds can include changes from many authors. It is not uncommon for your change to be included in a build that fails due to someone else's changes, or infrastructure issues. How to do this, and the rest of the post-merge process, is covered in detail here. If your change does cause a problem, it may be reverted, or you can revert it yourself. This is a normal part of LLVM development. You can fix your changes and open a new PR to merge them again. If you don't get any reports, no action is required from you. Your changes are working as expected, well done! |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/20669 Here is the relevant piece of the build log for the reference |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/154/builds/19723 Here is the relevant piece of the build log for the reference |
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It seems we are having issues on arm platforms, I will revert this patch. |
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Please, investigate this issue and when re-applying the reverted patch, commit message should be updated to indicate the problem that was addressed and how it was addressed. https://llvm.org/docs/DeveloperPolicy.html#patch-reversion-policy |
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…false positive for conditional expression" (#151859) Reverts llvm/llvm-project#139474 due to lit test failures on `arm` platforms.
AndreyG
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Aug 3, 2025
…conditional expression (llvm#139474) Let's consider the following code from the issue llvm#139467: ```c void test(int cond, char c) { char ret = cond > 0 ? ':' : c; } ``` Initializer of `ret` looks the following: ``` -ImplicitCastExpr 'char' <IntegralCast> `-ConditionalOperator 'int' |-BinaryOperator 'int' '>' | |-ImplicitCastExpr 'int' <LValueToRValue> | | `-DeclRefExpr 'int' lvalue ParmVar 'cond' 'int' | `-IntegerLiteral 'int' 0 |-CharacterLiteral 'int' 58 `-ImplicitCastExpr 'int' <IntegralCast> `-ImplicitCastExpr 'char' <LValueToRValue> `-DeclRefExpr 'char' lvalue ParmVar 'c' 'char' ``` So it could be seen that `RHS` of the conditional operator is `DeclRefExpr 'c'` which is casted to `int` and then the whole conditional expression is casted to 'char'. But this last conversion is not narrowing, because `RHS` was `char` _initially_. We should just remove the cast from `char` to `int` before the narrowing conversion check. Fixes llvm#139467 The added tests contains the implementation-defined warning about 'int' to 'char' conversion, which is not applicable to all platforms. And so the target is explictly set to 'x86_64' (the line 'RUN: -- -target x86_64-unknown-linux').
AndreyG
added a commit
to AndreyG/llvm-project
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Aug 3, 2025
…conditional expression (llvm#139474) Let's consider the following code from the issue llvm#139467: ```c void test(int cond, char c) { char ret = cond > 0 ? ':' : c; } ``` Initializer of `ret` looks the following: ``` -ImplicitCastExpr 'char' <IntegralCast> `-ConditionalOperator 'int' |-BinaryOperator 'int' '>' | |-ImplicitCastExpr 'int' <LValueToRValue> | | `-DeclRefExpr 'int' lvalue ParmVar 'cond' 'int' | `-IntegerLiteral 'int' 0 |-CharacterLiteral 'int' 58 `-ImplicitCastExpr 'int' <IntegralCast> `-ImplicitCastExpr 'char' <LValueToRValue> `-DeclRefExpr 'char' lvalue ParmVar 'c' 'char' ``` So it could be seen that `RHS` of the conditional operator is `DeclRefExpr 'c'` which is casted to `int` and then the whole conditional expression is casted to 'char'. But this last conversion is not narrowing, because `RHS` was `char` _initially_. We should just remove the cast from `char` to `int` before the narrowing conversion check. Fixes llvm#139467 The added tests contains the implementation-defined warning about 'int' to 'char' conversion, which is not applicable to all platforms. And so the target is explictly set to 'x86_64' (the line 'RUN: -- -target x86_64-unknown-linux').
AndreyG
added a commit
to AndreyG/llvm-project
that referenced
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Aug 3, 2025
…conditional expression (llvm#139474) Let's consider the following code from the issue llvm#139467: ```c void test(int cond, char c) { char ret = cond > 0 ? ':' : c; } ``` Initializer of `ret` looks the following: ``` -ImplicitCastExpr 'char' <IntegralCast> `-ConditionalOperator 'int' |-BinaryOperator 'int' '>' | |-ImplicitCastExpr 'int' <LValueToRValue> | | `-DeclRefExpr 'int' lvalue ParmVar 'cond' 'int' | `-IntegerLiteral 'int' 0 |-CharacterLiteral 'int' 58 `-ImplicitCastExpr 'int' <IntegralCast> `-ImplicitCastExpr 'char' <LValueToRValue> `-DeclRefExpr 'char' lvalue ParmVar 'c' 'char' ``` So it could be seen that `RHS` of the conditional operator is `DeclRefExpr 'c'` which is casted to `int` and then the whole conditional expression is casted to 'char'. But this last conversion is not narrowing, because `RHS` was `char` _initially_. We should just remove the cast from `char` to `int` before the narrowing conversion check. Fixes llvm#139467 The added tests contains the implementation-defined warning about 'int' to 'char' conversion, which is not applicable to all platforms. And so the target is explictly set to 'x86_64' (the line 'RUN: -- -target x86_64-unknown-linux').
vbvictor
pushed a commit
that referenced
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Aug 8, 2025
…ve for conditional expression" (#151874) This is another attempt to merge previously [reverted](#139474 (comment)) PR #139474. The added tests `narrowing-conversions-conditional-expressions.c[pp]` failed on [different (non x86_64) platforms](#139474 (comment)) because the expected warning is implementation-defined. That's why the test must explicitly specify target (the line `// RUN: -- -target x86_64-unknown-linux`).
llvm-sync bot
pushed a commit
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Aug 8, 2025
…lse positive for conditional expression" (#151874) This is another attempt to merge previously [reverted](llvm/llvm-project#139474 (comment)) PR #139474. The added tests `narrowing-conversions-conditional-expressions.c[pp]` failed on [different (non x86_64) platforms](llvm/llvm-project#139474 (comment)) because the expected warning is implementation-defined. That's why the test must explicitly specify target (the line `// RUN: -- -target x86_64-unknown-linux`).
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Let's consider the following code from the issue #139467:
Initializer of
retlooks the following:So it could be seen that
RHSof the conditional operator isDeclRefExpr 'c'which is casted tointand then the whole conditional expression is casted to 'char'. But this last conversion is not narrowing, becauseRHSwascharinitially. We should just remove the cast fromchartointbefore the narrowing conversion check.Fixes #139467