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[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
This commit is contained in:
Alexander Kornienko 2016-01-11 10:26:29 +00:00
parent d0f89cd721
commit dcbe5a9d17
2 changed files with 18 additions and 12 deletions
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18
clang-tools-extra/clang-tidy/google/MemsetZeroLengthCheck.cpp
View File

@ -51,25 +51,29 @@ static StringRef getAsString(const MatchFinder::MatchResult &Result,
void MemsetZeroLengthCheck::check(const MatchFinder::MatchResult &Result) {
const auto *Call = Result.Nodes.getNodeAs<CallExpr>("decl");
// Note, this is:
// void *memset(void *buffer, int fill_char, size_t byte_count);
// Arg1 is fill_char, Arg2 is byte_count.
const Expr *Arg1 = Call->getArg(1);
const Expr *Arg2 = Call->getArg(2);
// Try to evaluate the second argument so we can also find values that are not
// just literals.
// Return if `byte_count` is not zero at compile time.
llvm::APSInt Value1, Value2;
if (Arg2->isValueDependent() ||
!Arg2->EvaluateAsInt(Value2, *Result.Context) || Value2 != 0)
return;
// If both arguments evaluate to zero emit a warning without fix suggestions.
// Return if `fill_char` is known to be zero or negative at compile
// time. In these cases, swapping the args would be a nop, or
// introduce a definite bug. The code is likely correct.
if (!Arg1->isValueDependent() &&
Arg1->EvaluateAsInt(Value1, *Result.Context) &&
(Value1 == 0 || Value1.isNegative())) {
diag(Call->getLocStart(), "memset of size zero");
(Value1 == 0 || Value1.isNegative()))
return;
}
// Emit a warning and fix-its to swap the arguments.
// `byte_count` is known to be zero at compile time, and `fill_char` is
// either not known or known to be a positive integer. Emit a warning
// and fix-its to swap the arguments.
auto D = diag(Call->getLocStart(),
"memset of size zero, potentially swapped arguments");
SourceRange LHSRange = Arg1->getSourceRange();

12
clang-tools-extra/test/clang-tidy/google-runtime-memset-zero-length.cpp
View File

@ -48,13 +48,15 @@ void foo(void *a, int xsize, int ysize) {
memset(a, -1, sizeof(int));
memset(a, 0xcd, 1);
memset(a, v, 0);
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: memset of size zero
// CHECK-FIXES: memset(a, v, 0);
// Don't warn when the fill char and the length are both known to be
// zero. No bug is possible.
memset(a, 0, v);
memset(a, v, 0);
// -1 is clearly not a length by virtue of being negative, so no warning
// despite v == 0.
memset(a, -1, v);
// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: memset of size zero
// CHECK-FIXES: memset(a, -1, v);
memtmpl<0, int>();
}