[clang-tidy] Fix a false positive in google-runtime-memset
google-runtime-memset no longer issues a warning if the fill char value is known to be an invalid fill char count. Namely, it no longer warns for these: memset(p, 0, 0); memset(p, -1, 0); In both cases, swapping the last two args would either be useless (there is no actual bug) or wrong (it would introduce a bug). Patch by Matt Armstrong! llvm-svn: 257320
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@ -51,25 +51,29 @@ static StringRef getAsString(const MatchFinder::MatchResult &Result,
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void MemsetZeroLengthCheck::check(const MatchFinder::MatchResult &Result) {
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const auto *Call = Result.Nodes.getNodeAs<CallExpr>("decl");
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// Note, this is:
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// void *memset(void *buffer, int fill_char, size_t byte_count);
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// Arg1 is fill_char, Arg2 is byte_count.
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const Expr *Arg1 = Call->getArg(1);
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const Expr *Arg2 = Call->getArg(2);
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// Try to evaluate the second argument so we can also find values that are not
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// just literals.
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// Return if `byte_count` is not zero at compile time.
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llvm::APSInt Value1, Value2;
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if (Arg2->isValueDependent() ||
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!Arg2->EvaluateAsInt(Value2, *Result.Context) || Value2 != 0)
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return;
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// If both arguments evaluate to zero emit a warning without fix suggestions.
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// Return if `fill_char` is known to be zero or negative at compile
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// time. In these cases, swapping the args would be a nop, or
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// introduce a definite bug. The code is likely correct.
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if (!Arg1->isValueDependent() &&
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Arg1->EvaluateAsInt(Value1, *Result.Context) &&
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(Value1 == 0 || Value1.isNegative())) {
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diag(Call->getLocStart(), "memset of size zero");
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(Value1 == 0 || Value1.isNegative()))
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return;
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}
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// Emit a warning and fix-its to swap the arguments.
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// `byte_count` is known to be zero at compile time, and `fill_char` is
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// either not known or known to be a positive integer. Emit a warning
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// and fix-its to swap the arguments.
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auto D = diag(Call->getLocStart(),
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"memset of size zero, potentially swapped arguments");
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SourceRange LHSRange = Arg1->getSourceRange();
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@ -48,13 +48,15 @@ void foo(void *a, int xsize, int ysize) {
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memset(a, -1, sizeof(int));
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memset(a, 0xcd, 1);
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memset(a, v, 0);
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// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: memset of size zero
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// CHECK-FIXES: memset(a, v, 0);
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// Don't warn when the fill char and the length are both known to be
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// zero. No bug is possible.
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memset(a, 0, v);
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memset(a, v, 0);
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// -1 is clearly not a length by virtue of being negative, so no warning
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// despite v == 0.
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memset(a, -1, v);
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// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: memset of size zero
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// CHECK-FIXES: memset(a, -1, v);
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memtmpl<0, int>();
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}
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