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[ConstEval] Fix crash when comparing strings past the end #137078

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Merged
merged 1 commit into from
Apr 23, 2025
Merged

[ConstEval] Fix crash when comparing strings past the end #137078

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9 changes: 7 additions & 2 deletions clang/lib/AST/ExprConstant.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2234,10 +2234,15 @@ static bool ArePotentiallyOverlappingStringLiterals(const EvalInfo &Info,
// within RHS. We don't need to look at the characters of one string that
// would appear before the start of the other string if they were merged.
CharUnits Offset = RHS.Offset - LHS.Offset;
if (Offset.isNegative())
if (Offset.isNegative()) {
if (LHSString.Bytes.size() < (size_t)-Offset.getQuantity())
return false;
LHSString.Bytes = LHSString.Bytes.drop_front(-Offset.getQuantity());
else
} else {
if (RHSString.Bytes.size() < (size_t)Offset.getQuantity())
return false;
RHSString.Bytes = RHSString.Bytes.drop_front(Offset.getQuantity());
}

bool LHSIsLonger = LHSString.Bytes.size() > RHSString.Bytes.size();
StringRef Longer = LHSIsLonger ? LHSString.Bytes : RHSString.Bytes;
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9 changes: 9 additions & 0 deletions clang/test/AST/ByteCode/cxx20.cpp
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Expand Up @@ -119,6 +119,15 @@ constexpr auto b3 = name1() == name1(); // ref-error {{must be initialized by a
constexpr auto b4 = name1() == name2();
static_assert(!b4);

constexpr auto bar(const char *p) { return p + __builtin_strlen(p); }
constexpr auto b5 = bar(p1) == p1;
static_assert(!b5);
constexpr auto b6 = bar(p1) == ""; // ref-error {{must be initialized by a constant expression}} \
// ref-note {{comparison of addresses of potentially overlapping literals}}
constexpr auto b7 = bar(p1) + 1 == ""; // both-error {{must be initialized by a constant expression}} \
// ref-note {{comparison against pointer '&"test1"[6]' that points past the end of a complete object has unspecified value}} \
// expected-note {{comparison against pointer '&"test1"[6] + 1' that points past the end of a complete object has unspecified value}}
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@hnrklssn hnrklssn Apr 23, 2025 •
edited
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@tbaederr Not sure what causes the '&"test1"[6]' vs '&"test1"[6] + 1' discrepancy, but I thought I'd highlight it in case it isn't a known issue

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Hmm I may have been to quick with this, CI reports differently now. Reverting to check.


namespace UninitializedFields {
class A {
public:
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2 changes: 2 additions & 0 deletions clang/test/SemaCXX/constant-expression-cxx11.cpp
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Expand Up @@ -2199,6 +2199,8 @@ namespace BuiltinStrlen {
static_assert(__builtin_strlen("foo") == 3, "");
static_assert(__builtin_strlen("foo\0quux") == 3, "");
static_assert(__builtin_strlen("foo\0quux" + 4) == 4, "");
static_assert(__builtin_strlen("foo") + 1 + "foo" == "foo", ""); // expected-error {{static assertion expression is not an integral constant expression}}
// expected-note@-1 {{comparison against pointer '&"foo"[4]' that points past the end of a complete object has unspecified value}}

constexpr bool check(const char *p) {
return __builtin_strlen(p) == 3 &&
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