steakhal added inline comments.
================
Comment at: clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp:204
+ // subtraction/addition of the negated value.
+ if (!RHS.isNegative()) {
+ ConvertedRHS = &BasicVals.Convert(resultTy, RHS);
----------------
tomasz-kaminski-sonarsource wrote:
> steakhal wrote:
> > I would rather swap these branches though, to leave the default case (aka.
> > this) to the end.
> I folded the `RHS.isNegative()` into the if for the
> `BinaryOperator::isAssociative(op)`, as same conversion is performed in final
> else branch.
I think what confused me is that a different API is used for doing the
conversion.
- `resultIntTy.convert(RHS)`
- `&BasicVals.Convert(resultTy, RHS)`
Anyway, leave it as-is.
================
Comment at: clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp:212-219
+ llvm::APSInt ConvertedRHSValue = resultIntTy.convert(RHS);
+ // Check if the negation of the RHS is representable,
+ // i.e., the resultTy is signed, and it is not the lowest
+ // representable negative value.
+ if (ConvertedRHSValue > resultIntTy.getMinValue()) {
+ ConvertedRHS = &BasicVals.getValue(-ConvertedRHSValue);
+ op = (op == BO_Add) ? BO_Sub : BO_Add;
----------------
tomasz-kaminski-sonarsource wrote:
> tomasz-kaminski-sonarsource wrote:
> > steakhal wrote:
> > > Somehow I miss a check for signedness here.
> > > Why do you think it would be only triggered for signed types?
> > >
> > > I have a guess, that since we already handled `x +-0`, SymIntExprs like
> > > `x - (-0)` cannot exist here, thus cannot trigger this condition
> > > spuriously. I cannot think of any ther example that could cause this
> > > misbehaving. So in that sense `ConvertedRHSValue >
> > > resultIntTy.getMinValue()` implies *at this place* that
> > > `ConvertedRHSValue.isSigned()`.
> > > I would rather see this redundant check here to make the correctness
> > > reasoning local though.
> > The integer representation does not have negative zeros (the standard and
> > clang assume two's complement). However, this condition does need to check
> > for the signedness of the types. What I mean is that if the `RHS` is
> > negative, but `ConvertedRHSValue` the branch will trigger and we will
> > change `x - INT_MIN` to `x + (INT_MAX + 1)U` which is ok, as a negation of
> > `INT_MIN` is representable as an unsigned type of same or lager bit with.
> >
> However, I was not able to reach this point with `RHS` being signed, and
> `resultTy` being unsigned. Any hints how this could be done?
I'm not saying that I can follow this thought process. But the
`clang/test/Analysis/PR49642.c` would trigger an assertion like this:
```lang=diff
diff --git a/clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
b/clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
index 088c33c8e612..7e59309228e1 100644
--- a/clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
+++ b/clang/lib/StaticAnalyzer/Core/SimpleSValBuilder.cpp
@@ -207,6 +207,16 @@ SVal SimpleSValBuilder::MakeSymIntVal(const SymExpr *LHS,
"number of bits as its operands.");
llvm::APSInt ConvertedRHSValue = resultIntTy.convert(RHS);
+ if (RHS.isSigned() && resultTy->isUnsignedIntegerOrEnumerationType()) {
+ llvm::errs() << "LHS sym:\n";
+ LHS->dump();
+ llvm::errs() << "RHS integral:\n";
+ RHS.dump();
+ llvm::errs() << "OP: " << BinaryOperator::getOpcodeStr(op) << "\n";
+ llvm::errs() << "result type:\n";
+ resultTy->dump();
+ llvm_unreachable("how is it possible??");
+ }
// Check if the negation of the RHS is representable,
// i.e., the resultTy is signed, and it is not the lowest
// representable negative value.
```
Which can be reduced into this one:
```lang=c
// RUN: %clang_analyze_cc1 -Wno-implicit-function-declaration -w -verify %s \
// RUN: -analyzer-checker=core \
// RUN: -analyzer-checker=apiModeling.StdCLibraryFunctions
// expected-no-diagnostics
typedef int ssize_t;
int write(int, const void *, unsigned long);
unsigned c;
void a() {
int b = write(0, 0, c);
b != 0;
c -= b;
b < 1;
++c; // crash simplifySValOnce: derived_$4{conj_$1{int, LC1, S700, #1},c}
op(-) APInt(32b, 4294967295u -1s) :: unsigned int
}
```
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D124658/new/
https://reviews.llvm.org/D124658
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