Commit 6a36a695 authored by Hans Wennborg's avatar Hans Wennborg
Browse files

Merging r292555, r292558 and r292559:

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r292555 | rsmith | 2017-01-19 16:45:35 -0800 (Thu, 19 Jan 2017) | 6 lines

P0426: Make the library implementation of constexpr char_traits a little easier
by providing a memchr builtin that returns char* instead of void*.

Also add a __has_feature flag to indicate the presence of constexpr forms of
the relevant <string> functions.

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r292558 | rsmith | 2017-01-19 16:57:59 -0800 (Thu, 19 Jan 2017) | 2 lines

Add documentation for constexpr string builtin support.

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r292559 | rsmith | 2017-01-19 17:08:15 -0800 (Thu, 19 Jan 2017) | 2 lines

Fix documentation typo.

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git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_40@292807 91177308-0d34-0410-b5e6-96231b3b80d8
parent 2574fd71
......@@ -1776,6 +1776,46 @@ numeric primitives such as frexp. See `LLVM canonicalize intrinsic
<http://llvm.org/docs/LangRef.html#llvm-canonicalize-intrinsic>`_ for
more information on the semantics.
String builtins
---------------
Clang provides constant expression evaluation support for builtins forms of
the following functions from the C standard library ``<strings.h>`` header:
* ``memchr``
* ``memcmp``
* ``strchr``
* ``strcmp``
* ``strlen``
* ``strncmp``
* ``wcschr``
* ``wcscmp``
* ``wcslen``
* ``wcsncmp``
* ``wmemchr``
* ``wmemcmp``
In each case, the builtin form has the name of the C library function prefixed
by ``__builtin_``. Example:
.. code-block:: c
void *p = __builtin_memchr("foobar", 'b', 5);
In addition to the above, one further builtin is provided:
.. code-block:: c
char *__builtin_char_memchr(const char *haystack, int needle, size_t size);
``__builtin_char_memchr(a, b, c)`` is identical to
``(char*)__builtin_memchr(a, b, c)`` except that its use is permitted within
constant expressions in C++11 onwards (where a cast from ``void*`` to ``char*``
is disallowed in general).
Support for constant expression evaluation for the above builtins be detected
with ``__has_feature(cxx_constexpr_string_builtins)``.
.. _langext-__c11_atomic:
__c11_atomic builtins
......
......@@ -1339,6 +1339,7 @@ BUILTIN(__builtin_smulll_overflow, "bSLLiCSLLiCSLLi*", "n")
BUILTIN(__builtin_addressof, "v*v&", "nct")
BUILTIN(__builtin_operator_new, "v*z", "c")
BUILTIN(__builtin_operator_delete, "vv*", "n")
BUILTIN(__builtin_char_memchr, "c*cC*iz", "n")
// Safestack builtins
BUILTIN(__builtin___get_unsafe_stack_start, "v*", "Fn")
......
......@@ -5683,6 +5683,7 @@ bool PointerExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
case Builtin::BI__builtin_strchr:
case Builtin::BI__builtin_wcschr:
case Builtin::BI__builtin_memchr:
case Builtin::BI__builtin_char_memchr:
case Builtin::BI__builtin_wmemchr: {
if (!Visit(E->getArg(0)))
return false;
......@@ -5720,6 +5721,7 @@ bool PointerExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
// Fall through.
case Builtin::BImemchr:
case Builtin::BI__builtin_memchr:
case Builtin::BI__builtin_char_memchr:
// memchr compares by converting both sides to unsigned char. That's also
// correct for strchr if we get this far (to cope with plain char being
// unsigned in the strchr case).
......
......@@ -1189,6 +1189,10 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
return RValue::get(Dest.getPointer());
}
case Builtin::BI__builtin_char_memchr:
BuiltinID = Builtin::BI__builtin_memchr;
break;
case Builtin::BI__builtin___memcpy_chk: {
// fold __builtin_memcpy_chk(x, y, cst1, cst2) to memcpy iff cst1<=cst2.
llvm::APSInt Size, DstSize;
......
......@@ -1183,6 +1183,7 @@ static bool HasFeature(const Preprocessor &PP, StringRef Feature) {
.Case("cxx_attributes", LangOpts.CPlusPlus11)
.Case("cxx_auto_type", LangOpts.CPlusPlus11)
.Case("cxx_constexpr", LangOpts.CPlusPlus11)
.Case("cxx_constexpr_string_builtins", LangOpts.CPlusPlus11)
.Case("cxx_decltype", LangOpts.CPlusPlus11)
.Case("cxx_decltype_incomplete_return_types", LangOpts.CPlusPlus11)
.Case("cxx_default_function_template_args", LangOpts.CPlusPlus11)
......
......@@ -26,3 +26,7 @@ int x = __builtin_abs(-2);
long y = __builtin_abs(-2l);
// CHECK: [[Y:%.+]] = call i64 @_Z13__builtin_absl(i64 -2)
// CHECK: store i64 [[Y]], i64* @y, align 8
extern const char char_memchr_arg[32];
char *memchr_result = __builtin_char_memchr(char_memchr_arg, 123, 32);
// CHECK: call i8* @memchr(i8* getelementptr inbounds ([32 x i8], [32 x i8]* @char_memchr_arg, i32 0, i32 0), i32 123, i64 32)
......@@ -301,6 +301,17 @@ int no_constexpr();
// CHECK-11: has_constexpr
// CHECK-NO-11: no_constexpr
#if __has_feature(cxx_constexpr_string_builtins)
int has_constexpr_string_builtins();
#else
int no_constexpr_string_builtins();
#endif
// CHECK-1Z: has_constexpr_string_builtins
// CHECK-14: has_constexpr_string_builtins
// CHECK-11: has_constexpr_string_builtins
// CHECK-NO-11: no_constexpr_string_builtins
#if __has_feature(cxx_generalized_initializers)
int has_generalized_initializers();
#else
......
......@@ -166,6 +166,27 @@ namespace StrchrEtc {
static_assert(__builtin_memchr(nullptr, 'x', 3) == nullptr); // expected-error {{not an integral constant}} expected-note {{dereferenced null}}
static_assert(__builtin_memchr(nullptr, 'x', 0) == nullptr); // FIXME: Should we reject this?
static_assert(__builtin_char_memchr(kStr, 'a', 0) == nullptr);
static_assert(__builtin_char_memchr(kStr, 'a', 1) == kStr);
static_assert(__builtin_char_memchr(kStr, '\0', 5) == nullptr);
static_assert(__builtin_char_memchr(kStr, '\0', 6) == kStr + 5);
static_assert(__builtin_char_memchr(kStr, '\xff', 8) == kStr + 4);
static_assert(__builtin_char_memchr(kStr, '\xff' + 256, 8) == kStr + 4);
static_assert(__builtin_char_memchr(kStr, '\xff' - 256, 8) == kStr + 4);
static_assert(__builtin_char_memchr(kFoo, 'x', 3) == nullptr);
static_assert(__builtin_char_memchr(kFoo, 'x', 4) == nullptr); // expected-error {{not an integral constant}} expected-note {{dereferenced one-past-the-end}}
static_assert(__builtin_char_memchr(nullptr, 'x', 3) == nullptr); // expected-error {{not an integral constant}} expected-note {{dereferenced null}}
static_assert(__builtin_char_memchr(nullptr, 'x', 0) == nullptr); // FIXME: Should we reject this?
static_assert(*__builtin_char_memchr(kStr, '\xff', 8) == '\xff');
constexpr bool char_memchr_mutable() {
char buffer[] = "mutable";
*__builtin_char_memchr(buffer, 't', 8) = 'r';
*__builtin_char_memchr(buffer, 'm', 8) = 'd';
return __builtin_strcmp(buffer, "durable") == 0;
}
static_assert(char_memchr_mutable());
constexpr bool a = !strchr("hello", 'h'); // expected-error {{constant expression}} expected-note {{non-constexpr function 'strchr' cannot be used in a constant expression}}
constexpr bool b = !memchr("hello", 'h', 3); // expected-error {{constant expression}} expected-note {{non-constexpr function 'memchr' cannot be used in a constant expression}}
}
......
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