C++: Fix missing bool -> int conversions in C code
#20145
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Pull Request Overview
This PR fixes missing bool to int conversions in C code that were causing type errors in the IR. When comparisons and other boolean operations in C code store their results to integer variables, the IR previously showed incorrect type mismatches where boolean values were being stored to integer memory locations.
- Adds
TranslatedSyntheticBoolToIntConversionclass to handle bool-to-int conversions - Introduces
hasTranslatedSyntheticBoolToIntConversionpredicate to identify expressions needing conversion - Updates instruction tags and test expectations to reflect the new conversion instructions
Reviewed Changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.
Show a summary per file
| File | Description |
|---|---|
| cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedExpr.qll | Adds TranslatedSyntheticBoolToIntConversion class and updates core expression handling |
| cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedElement.qll | Adds predicate logic to identify expressions needing bool-to-int conversion |
| cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/InstructionTag.qll | Adds BoolToIntConversionTag for the new conversion instruction |
| cpp/ql/test/library-tests/ir/ir/ir.c | Adds test case for double negation assignment |
| cpp/ql/test/library-tests/ir/ir/raw_ir.expected | Updates expected IR output to include new conversion instructions |
| cpp/ql/test/library-tests/ir/ir/aliased_ir.expected | Updates expected aliased IR output with conversion instructions |
| cpp/ql/test/library-tests/ir/ir/PrintAST.expected | Updates expected AST output for new test case |
Comments suppressed due to low confidence (1)
cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedElement.qll:530
- The predicate name
parentExpectsBoolis misleading. It should be named something likeparentExpectsBoolValueorusedInBooleanContextsince it checks if the child expression is used in a context where a boolean value is expected, not just any parent.
private predicate parentExpectsBool(Expr child) {
any(NotExpr notExpr).getOperand() = child
or
usedAsCondition(child)
}
jketema
approved these changes
Aug 11, 2025
This was referenced Aug 13, 2025
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In #18490 we fixed a number of discrepancies between IR generated from C code, and IR generated from C++ code. For example, the following code has a int-to-bool conversion in the AST on
xat the conditional when compiled as C++, but not when compiled as C:#18490 removed this discrepancy in the IR by synthesizing the equivalent int-to-bool conversion when generating IR. One of the things we did was adjust the
IRTypereturned by various operations (see here)However, when I was working on something else I noticed that this change introduced a type error in the IR on examples such as:
Because
a < bhas been overwritten to return a boolean, theStoreInstructioncorresponding to the initialization ofxlooks like:In particular, notice that we are storing a result of type
boolinto a memory address of typeglval<int>. That's not allowed in the IR, and it gives some false negatives in the guards library.This PR fixes that by adding the necessary bool-to-int conversions when such type errors would have occurred in the IR.
Commit-by-commit review highly encouraged.
DCA shows a couple new results for
cpp/missing-check-scanf. They look like FPs caused by insufficient guards logic (which we now need now that those conditionals are properly handled in the IR). I will take a look at once this PR has been merged.