Clang supports a number of builtin library functions with the same syntax as
GCC, including things like ``__builtin_nan``, ``__builtin_constant_p``,
``__builtin_choose_expr``, ``__builtin_types_compatible_p``,
-``__sync_fetch_and_add``, etc. In addition to the GCC builtins, Clang supports
-a number of builtins that GCC does not, which are listed here.
+``__builtin_assume_aligned``, ``__sync_fetch_and_add``, etc. In addition to
+the GCC builtins, Clang supports a number of builtins that GCC does not, which
+are listed here.
Please note that Clang does not and will not support all of the GCC builtins
for vector operations. Instead of using builtins, you should use the functions
<langext-vectors>` instead of builtins, in order to reduce the number of
builtins that we need to implement.
+``__builtin_assume``
+------------------------------
+
+``__builtin_assume`` is used to provide the optimizer with a boolean
+invariant that is defined to be true.
+
+**Syntax**:
+
+.. code-block:: c++
+
+ __builtin_assume(bool)
+
+**Example of Use**:
+
+.. code-block:: c++
+
+ int foo(int x) {
+ __builtin_assume(x != 0);
+
+ // The optimizer may short-circuit this check using the invariant.
+ if (x == 0)
+ return do_something();
+
+ return do_something_else();
+ }
+
+**Description**:
+
+The boolean argument to this function is defined to be true. The optimizer may
+analyze the form of the expression provided as the argument and deduce from
+that information used to optimize the program. If the condition is violated
+during execution, the behavior is undefined. The argument itself is never
+evaluated, so any side effects of the expression will be discarded.
+
+Query for this feature with ``__has_builtin(__builtin_assume)``.
+
``__builtin_readcyclecounter``
------------------------------
BUILTIN(__builtin_va_end, "vA", "n")
BUILTIN(__builtin_va_copy, "vAA", "n")
BUILTIN(__builtin_stdarg_start, "vA.", "n")
+BUILTIN(__builtin_assume_aligned, "v*vC*z.", "nc")
BUILTIN(__builtin_bcmp, "iv*v*z", "n")
BUILTIN(__builtin_bcopy, "vv*v*z", "n")
BUILTIN(__builtin_bzero, "vv*z", "nF")
// Annotation function
BUILTIN(__builtin_annotation, "v.", "tn")
+// Invariants
+BUILTIN(__builtin_assume, "vb", "n")
+
// Multiprecision Arithmetic Builtins.
BUILTIN(__builtin_addcb, "UcUcCUcCUcCUc*", "n")
BUILTIN(__builtin_addcs, "UsUsCUsCUsCUs*", "n")
"the terminating null byte">;
def warn_assume_side_effects : Warning<
- "the argument to __assume has side effects that will be discarded">,
+ "the argument to %0 has side effects that will be discarded">,
InGroup<DiagGroup<"assume">>;
/// main()
def error_cannot_find_suitable_accessor : Error<
"cannot find suitable %select{getter|setter}0 for property %1">;
-def err_attribute_aligned_not_power_of_two : Error<
+def err_alignment_not_power_of_two : Error<
"requested alignment is not a power of 2">;
+
def err_attribute_aligned_too_great : Error<
"requested alignment must be %0 bytes or smaller">;
def warn_redeclaration_without_attribute_prev_attribute_ignored : Warning<
private:
bool SemaBuiltinPrefetch(CallExpr *TheCall);
bool SemaBuiltinAssume(CallExpr *TheCall);
+ bool SemaBuiltinAssumeAligned(CallExpr *TheCall);
bool SemaBuiltinLongjmp(CallExpr *TheCall);
ExprResult SemaBuiltinAtomicOverloaded(ExprResult TheCallResult);
ExprResult SemaAtomicOpsOverloaded(ExprResult TheCallResult,
return Success(Operand, E);
}
+ case Builtin::BI__builtin_assume_aligned:
case Builtin::BI__builtin_expect:
return Visit(E->getArg(0));
default:
return ExprEvaluatorBaseTy::VisitCallExpr(E);
case Builtin::BI__assume:
+ case Builtin::BI__builtin_assume:
// The argument is not evaluated!
return true;
}
"expval");
return RValue::get(Result);
}
+ case Builtin::BI__builtin_assume_aligned: {
+ Value *PtrValue = EmitScalarExpr(E->getArg(0));
+ Value *OffsetValue =
+ (E->getNumArgs() > 2) ? EmitScalarExpr(E->getArg(2)) : nullptr;
+
+ Value *AlignmentValue = EmitScalarExpr(E->getArg(1));
+ ConstantInt *AlignmentCI = cast<ConstantInt>(AlignmentValue);
+ unsigned Alignment = (unsigned) AlignmentCI->getZExtValue();
+
+ EmitAlignmentAssumption(PtrValue, Alignment, OffsetValue);
+ return RValue::get(PtrValue);
+ }
+ case Builtin::BI__assume:
+ case Builtin::BI__builtin_assume: {
+ if (E->getArg(0)->HasSideEffects(getContext()))
+ return RValue::get(nullptr);
+
+ Value *ArgValue = EmitScalarExpr(E->getArg(0));
+ Value *FnAssume = CGM.getIntrinsic(Intrinsic::assume);
+ return RValue::get(Builder.CreateCall(FnAssume, ArgValue));
+ }
case Builtin::BI__builtin_bswap16:
case Builtin::BI__builtin_bswap32:
case Builtin::BI__builtin_bswap64: {
case Builtin::BI__noop:
// __noop always evaluates to an integer literal zero.
return RValue::get(ConstantInt::get(IntTy, 0));
- case Builtin::BI__assume:
- // Until LLVM supports assumptions at the IR level, this becomes nothing.
- return RValue::get(nullptr);
case Builtin::BI_InterlockedExchange:
case Builtin::BI_InterlockedExchangePointer:
return EmitBinaryAtomic(*this, llvm::AtomicRMWInst::Xchg, E);
return isPre ? IncVal : InVal;
}
+void CodeGenFunction::EmitAlignmentAssumption(llvm::Value *PtrValue,
+ unsigned Alignment,
+ llvm::Value *OffsetValue) {
+ llvm::Value *PtrIntValue =
+ Builder.CreatePtrToInt(PtrValue, IntPtrTy, "ptrint");
+
+ llvm::Value *Mask = llvm::ConstantInt::get(IntPtrTy,
+ Alignment > 0 ? Alignment - 1 : 0);
+ if (OffsetValue) {
+ bool IsOffsetZero = false;
+ if (llvm::ConstantInt *CI = dyn_cast<llvm::ConstantInt>(OffsetValue))
+ IsOffsetZero = CI->isZero();
+
+ if (!IsOffsetZero) {
+ if (OffsetValue->getType() != IntPtrTy)
+ OffsetValue = Builder.CreateIntCast(OffsetValue, IntPtrTy,
+ /*isSigned*/true, "offsetcast");
+ PtrIntValue = Builder.CreateSub(PtrIntValue, OffsetValue, "offsetptr");
+ }
+ }
+
+ llvm::Value *Zero = llvm::ConstantInt::get(IntPtrTy, 0);
+ llvm::Value *MaskedPtr = Builder.CreateAnd(PtrIntValue, Mask, "maskedptr");
+ llvm::Value *InvCond = Builder.CreateICmpEQ(MaskedPtr, Zero, "maskcond");
+
+ llvm::Value *FnAssume = CGM.getIntrinsic(llvm::Intrinsic::assume);
+ Builder.CreateCall(FnAssume, InvCond);
+}
//===----------------------------------------------------------------------===//
// LValue Expression Emission
bool isInc, bool isPre);
ComplexPairTy EmitComplexPrePostIncDec(const UnaryOperator *E, LValue LV,
bool isInc, bool isPre);
+
+ void EmitAlignmentAssumption(llvm::Value *PtrValue, unsigned Alignment,
+ llvm::Value *OffsetValue = nullptr);
+
//===--------------------------------------------------------------------===//
// Declaration Emission
//===--------------------------------------------------------------------===//
return ExprError();
break;
case Builtin::BI__assume:
+ case Builtin::BI__builtin_assume:
if (SemaBuiltinAssume(TheCall))
return ExprError();
break;
+ case Builtin::BI__builtin_assume_aligned:
+ if (SemaBuiltinAssumeAligned(TheCall))
+ return ExprError();
+ break;
case Builtin::BI__builtin_object_size:
if (SemaBuiltinConstantArgRange(TheCall, 1, 0, 3))
return ExprError();
if (Arg->HasSideEffects(Context))
return Diag(Arg->getLocStart(), diag::warn_assume_side_effects)
- << Arg->getSourceRange();
+ << Arg->getSourceRange()
+ << cast<FunctionDecl>(TheCall->getCalleeDecl())->getIdentifier();
+
+ return false;
+}
+
+/// Handle __builtin_assume_aligned. This is declared
+/// as (const void*, size_t, ...) and can take one optional constant int arg.
+bool Sema::SemaBuiltinAssumeAligned(CallExpr *TheCall) {
+ unsigned NumArgs = TheCall->getNumArgs();
+
+ if (NumArgs > 3)
+ return Diag(TheCall->getLocEnd(),
+ diag::err_typecheck_call_too_many_args_at_most)
+ << 0 /*function call*/ << 3 << NumArgs
+ << TheCall->getSourceRange();
+
+ // The alignment must be a constant integer.
+ Expr *Arg = TheCall->getArg(1);
+
+ // We can't check the value of a dependent argument.
+ if (!Arg->isTypeDependent() && !Arg->isValueDependent()) {
+ llvm::APSInt Result;
+ if (SemaBuiltinConstantArg(TheCall, 1, Result))
+ return true;
+
+ if (!Result.isPowerOf2())
+ return Diag(TheCall->getLocStart(),
+ diag::err_alignment_not_power_of_two)
+ << Arg->getSourceRange();
+ }
+
+ if (NumArgs > 2) {
+ ExprResult Arg(TheCall->getArg(2));
+ InitializedEntity Entity = InitializedEntity::InitializeParameter(Context,
+ Context.getSizeType(), false);
+ Arg = PerformCopyInitialization(Entity, SourceLocation(), Arg);
+ if (Arg.isInvalid()) return true;
+ TheCall->setArg(2, Arg.get());
+ }
return false;
}
// An alignment specification of zero has no effect.
if (!(TmpAttr.isAlignas() && !Alignment) &&
!llvm::isPowerOf2_64(Alignment.getZExtValue())) {
- Diag(AttrLoc, diag::err_attribute_aligned_not_power_of_two)
+ Diag(AttrLoc, diag::err_alignment_not_power_of_two)
<< E->getSourceRange();
return;
}
--- /dev/null
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s | FileCheck %s
+
+// CHECK-LABEL: @test1
+int test1(int *a) {
+// CHECK: %ptrint = ptrtoint
+// CHECK: %maskedptr = and i64 %ptrint, 31
+// CHECK: %maskcond = icmp eq i64 %maskedptr, 0
+// CHECK: call void @llvm.assume(i1 %maskcond)
+ a = __builtin_assume_aligned(a, 32, 0ull);
+ return a[0];
+}
+
+// CHECK-LABEL: @test2
+int test2(int *a) {
+// CHECK: %ptrint = ptrtoint
+// CHECK: %maskedptr = and i64 %ptrint, 31
+// CHECK: %maskcond = icmp eq i64 %maskedptr, 0
+// CHECK: call void @llvm.assume(i1 %maskcond)
+ a = __builtin_assume_aligned(a, 32, 0);
+ return a[0];
+}
+
+// CHECK-LABEL: @test3
+int test3(int *a) {
+// CHECK: %ptrint = ptrtoint
+// CHECK: %maskedptr = and i64 %ptrint, 31
+// CHECK: %maskcond = icmp eq i64 %maskedptr, 0
+// CHECK: call void @llvm.assume(i1 %maskcond)
+ a = __builtin_assume_aligned(a, 32);
+ return a[0];
+}
+
+// CHECK-LABEL: @test4
+int test4(int *a, int b) {
+// CHECK-DAG: %ptrint = ptrtoint
+// CHECK-DAG: %conv = sext i32
+// CHECK: %offsetptr = sub i64 %ptrint, %conv
+// CHECK: %maskedptr = and i64 %offsetptr, 31
+// CHECK: %maskcond = icmp eq i64 %maskedptr, 0
+// CHECK: call void @llvm.assume(i1 %maskcond)
+ a = __builtin_assume_aligned(a, 32, b);
+ return a[0];
+}
+
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s | FileCheck %s
// RUN: %clang_cc1 -triple i386-mingw32 -fms-extensions -emit-llvm -o - %s | FileCheck %s
// CHECK-LABEL: @test1
-int test1(int *a) {
- __assume(a != 0);
+int test1(int *a, int i) {
+// CHECK: %0 = load i32** %a.addr
+// CHECK: %cmp = icmp ne i32* %0, null
+// CHECK: call void @llvm.assume(i1 %cmp)
+#ifdef _MSC_VER
+ __assume(a != 0)
+#else
+ __builtin_assume(a != 0);
+#endif
+
+// Nothing is generated for an assume with side effects...
+// CHECK-NOT: load i32** %i.addr
+// CHECK-NOT: call void @llvm.assume
+#ifdef _MSC_VER
+ __assume(++i != 0)
+#else
+ __builtin_assume(++i != 0);
+#endif
+
return a[0];
}
--- /dev/null
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+int test1(int *a) {
+ a = __builtin_assume_aligned(a, 32, 0ull);
+ return a[0];
+}
+
+int test2(int *a) {
+ a = __builtin_assume_aligned(a, 32, 0);
+ return a[0];
+}
+
+int test3(int *a) {
+ a = __builtin_assume_aligned(a, 32);
+ return a[0];
+}
+
+int test4(int *a) {
+ a = __builtin_assume_aligned(a, -32); // expected-error {{requested alignment is not a power of 2}}
+ a = __builtin_assume_aligned(a, 1ULL << 63);
+ return a[0];
+}
+
+int test5(int *a, unsigned *b) {
+ a = __builtin_assume_aligned(a, 32, b); // expected-warning {{incompatible pointer to integer conversion passing 'unsigned int *' to parameter of type}}
+ return a[0];
+}
+
+int test6(int *a) {
+ a = __builtin_assume_aligned(a, 32, 0, 0); // expected-error {{too many arguments to function call, expected at most 3, have 4}}
+ return a[0];
+}
+
+int test7(int *a) {
+ a = __builtin_assume_aligned(a, 31); // expected-error {{requested alignment is not a power of 2}}
+ return a[0];
+}
+
+int test8(int *a, int j) {
+ a = __builtin_assume_aligned(a, j); // expected-error {{must be a constant integer}}
+ return a[0];
+}
+
// RUN: %clang_cc1 -triple i386-mingw32 -fms-extensions -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fsyntax-only -verify %s
int foo(int *a, int i) {
+#ifdef _MSC_VER
__assume(i != 4);
- __assume(++i > 2); //expected-warning {{the argument to __assume has side effects that will be discarded}}
+ __assume(++i > 2); //expected-warning {{the argument to '__assume' has side effects that will be discarded}}
int test = sizeof(struct{char qq[(__assume(i != 5), 7)];});
+#else
+ __builtin_assume(i != 4);
+ __builtin_assume(++i > 2); //expected-warning {{the argument to '__builtin_assume' has side effects that will be discarded}}
+ int test = sizeof(struct{char qq[(__builtin_assume(i != 5), 7)];});
+#endif
return a[i];
}
--- /dev/null
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+template<int z>
+int test9(int *a) {
+ a = (int *) __builtin_assume_aligned(a, z + 1); // expected-error {{requested alignment is not a power of 2}}
+ return a[0];
+}
+
+void test9i(int *a) {
+ test9<42>(a); // expected-note {{in instantiation of function template specialization 'test9<42>' requested here}}
+}
+
+template<typename T>
+int test10(int *a, T z) {
+ a = (int *) __builtin_assume_aligned(a, z + 1); // expected-error {{must be a constant integer}}
+ return a[0];
+}
+
+int test10i(int *a) {
+ return test10(a, 42); // expected-note {{in instantiation of function template specialization 'test10<int>' requested here}}
+}
+
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