zoecarver created this revision.
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Adds `__builtin_zero_non_value_bits` to zero all padding bits of a
struct.
Currently does not support unions or bitfields.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D87974
Files:
clang/include/clang/Basic/Builtins.def
clang/lib/CodeGen/CGBuiltin.cpp
clang/lib/Sema/SemaChecking.cpp
clang/test/CodeGenCXX/builtin-zero-non-value-bits.cpp
clang/test/SemaCXX/builtin-zero-non-value-bits.cpp
Index: clang/test/SemaCXX/builtin-zero-non-value-bits.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/builtin-zero-non-value-bits.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+struct Foo { };
+
+void test(int a, Foo b, void* c, int *d, Foo *e) {
+ __builtin_zero_non_value_bits(a); // expected-error {{passing 'int' to parameter of incompatible type structure pointer: type mismatch at 1st parameter ('int' vs structure pointer)}}
+ __builtin_zero_non_value_bits(b); // expected-error {{passing 'Foo' to parameter of incompatible type structure pointer: type mismatch at 1st parameter ('Foo' vs structure pointer)}}
+ __builtin_zero_non_value_bits(c); // expected-error {{passing 'void *' to parameter of incompatible type structure pointer: type mismatch at 1st parameter ('void *' vs structure pointer)}}
+ __builtin_zero_non_value_bits(d); // expected-error {{passing 'int *' to parameter of incompatible type structure pointer: type mismatch at 1st parameter ('int *' vs structure pointer)}}
+ __builtin_zero_non_value_bits(e); // This should not error.
+}
Index: clang/test/CodeGenCXX/builtin-zero-non-value-bits.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/builtin-zero-non-value-bits.cpp
@@ -0,0 +1,171 @@
+// RUN: mkdir -p %t
+// RUN: %clang++ %s -o %t/run
+// RUN: %t/run
+
+#include <cstdio>
+#include <cstring>
+#include <cassert>
+
+template<size_t A1, size_t A2, class T>
+struct alignas(A1) BasicWithPadding {
+ T x;
+ alignas(A2) T y;
+};
+
+template<size_t A1, size_t A2, size_t N, class T>
+struct alignas(A1) ArrWithPadding {
+ T x[N];
+ alignas(A2) char c;
+ T y[N];
+};
+
+template<size_t A1, size_t A2, class T>
+struct alignas(A1) PtrWithPadding {
+ T *x;
+ alignas(A2) T *y;
+};
+
+template<size_t A1, size_t A2, size_t A3, class T>
+struct alignas(A1) ThreeWithPadding {
+ T x;
+ alignas(A2) T y;
+ alignas(A3) T z;
+};
+
+template<class T>
+struct Normal {
+ T a;
+ T b;
+};
+
+template<class T>
+struct X {
+ T x;
+};
+
+template<class T>
+struct Z {
+ T z;
+};
+
+template<size_t A, class T>
+struct YZ : public Z<T> {
+ alignas(A) T y;
+};
+
+template<size_t A1, size_t A2, class T>
+struct alignas(A1) HasBase : public X<T>, public YZ<A2, T> {
+ T a;
+ alignas(A2) T b;
+};
+
+template<size_t A1, size_t A2, class T>
+void testAllForType(T a, T b, T c, T d) {
+ using B = BasicWithPadding<A1, A2, T>;
+ B basic1;
+ memset(&basic1, 0, sizeof(B));
+ basic1.x = a;
+ basic1.y = b;
+ B basic2;
+ memset(&basic2, 42, sizeof(B));
+ basic2.x = a;
+ basic2.y = b;
+ assert(memcmp(&basic1, &basic2, sizeof(B)) != 0);
+ __builtin_zero_non_value_bits(&basic2);
+ assert(memcmp(&basic1, &basic2, sizeof(B)) == 0);
+
+ using A = ArrWithPadding<A1, A2, 2, T>;
+ A arr1;
+ memset(&arr1, 0, sizeof(A));
+ arr1.x[0] = a;
+ arr1.x[1] = b;
+ arr1.y[0] = c;
+ arr1.y[1] = d;
+ A arr2;
+ memset(&arr2, 42, sizeof(A));
+ arr2.x[0] = a;
+ arr2.x[1] = b;
+ arr2.y[0] = c;
+ arr2.y[1] = d;
+ arr2.c = 0;
+ assert(memcmp(&arr1, &arr2, sizeof(A)) != 0);
+ __builtin_zero_non_value_bits(&arr2);
+ assert(memcmp(&arr1, &arr2, sizeof(A)) == 0);
+
+ using P = PtrWithPadding<A1, A2, T>;
+ P ptr1;
+ memset(&ptr1, 0, sizeof(P));
+ ptr1.x = &a;
+ ptr1.y = &b;
+ P ptr2;
+ memset(&ptr2, 42, sizeof(P));
+ ptr2.x = &a;
+ ptr2.y = &b;
+ assert(memcmp(&ptr1, &ptr2, sizeof(P)) != 0);
+ __builtin_zero_non_value_bits(&ptr2);
+ assert(memcmp(&ptr1, &ptr2, sizeof(P)) == 0);
+
+ using Three = ThreeWithPadding<A1, A2, A2, T>;
+ Three three1;
+ memset(&three1, 0, sizeof(Three));
+ three1.x = a;
+ three1.y = b;
+ three1.z = c;
+ Three three2;
+ memset(&three2, 42, sizeof(Three));
+ three2.x = a;
+ three2.y = b;
+ three2.z = c;
+ __builtin_zero_non_value_bits(&three2);
+ assert(memcmp(&three1, &three2, sizeof(Three)) == 0);
+
+ using N = Normal<T>;
+ N normal1;
+ memset(&normal1, 0, sizeof(N));
+ normal1.a = a;
+ normal1.b = b;
+ N normal2;
+ memset(&normal2, 42, sizeof(N));
+ normal2.a = a;
+ normal2.b = b;
+ __builtin_zero_non_value_bits(&normal2);
+ assert(memcmp(&normal1, &normal2, sizeof(N)) == 0);
+
+ using H = HasBase<A1, A2, T>;
+ H base1;
+ memset(&base1, 0, sizeof(H));
+ base1.a = a;
+ base1.b = b;
+ base1.x = c;
+ base1.y = d;
+ base1.z = a;
+ H base2;
+ memset(&base2, 42, sizeof(H));
+ base2.a = a;
+ base2.b = b;
+ base2.x = c;
+ base2.y = d;
+ base2.z = a;
+ assert(memcmp(&base1, &base2, sizeof(H)) != 0);
+ __builtin_zero_non_value_bits(&base2);
+ unsigned i = 0;
+ assert(memcmp(&base1, &base2, sizeof(H)) == 0);
+}
+
+struct Foo {
+ int x;
+ int y;
+};
+
+int main() {
+ testAllForType<32, 16, char>(11, 22, 33, 44);
+ testAllForType<64, 32, char>(4, 5, 6, 7);
+ testAllForType<32, 16, int>(0, 1, 2, 3);
+ testAllForType<64, 32, int>(4, 5, 6, 7);
+ testAllForType<32, 16, double>(0, 1, 2, 3);
+ testAllForType<64, 32, double>(4, 5, 6, 7);
+ testAllForType<32, 16, Foo>(Foo{1, 2}, Foo{3, 4}, Foo{1, 2}, Foo{3, 4});
+ testAllForType<64, 32, Foo>(Foo{1, 2}, Foo{3, 4}, Foo{1, 2}, Foo{3, 4});
+
+ return 0;
+}
Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -1593,6 +1593,18 @@
}
case Builtin::BI__builtin_launder:
return SemaBuiltinLaunder(*this, TheCall);
+ case Builtin::BI__builtin_zero_non_value_bits: {
+ const Expr *PtrArg = TheCall->getArg(0)->IgnoreParenImpCasts();
+ const QualType PtrArgType = PtrArg->getType();
+ if (!PtrArgType->isPointerType() ||
+ !PtrArgType->getPointeeType()->isRecordType()) {
+ Diag(PtrArg->getBeginLoc(), diag::err_typecheck_convert_incompatible)
+ << PtrArgType << "structure pointer" << 1 << 0 << 3 << 1 << PtrArgType
+ << "structure pointer";
+ return ExprError();
+ }
+ break;
+ }
case Builtin::BI__sync_fetch_and_add:
case Builtin::BI__sync_fetch_and_add_1:
case Builtin::BI__sync_fetch_and_add_2:
Index: clang/lib/CodeGen/CGBuiltin.cpp
===================================================================
--- clang/lib/CodeGen/CGBuiltin.cpp
+++ clang/lib/CodeGen/CGBuiltin.cpp
@@ -1642,6 +1642,71 @@
return RValue::get(Builder.CreateCall(F, { Src, Src, ShiftAmt }));
}
+static void RecursivelyZeroNonValueBits(CodeGenFunction &CGF, Value *Ptr,
+ QualType Ty) {
+ auto *I8Ptr = CGF.Builder.CreateBitCast(Ptr, CGF.Int8PtrTy);
+ auto *Zero = ConstantInt::get(CGF.Int8Ty, 0);
+ auto WriteZeroAtOffset = [&](size_t Offset) {
+ auto Index = ConstantInt::get(CGF.IntTy, Offset);
+ auto Element = CGF.Builder.CreateGEP(I8Ptr, Index);
+ CGF.Builder.CreateAlignedStore(Zero, Element, MaybeAlign());
+ };
+ auto GetStructLayout = [&CGF](llvm::Type *Ty) {
+ auto ST = cast<StructType>(Ty);
+ return CGF.CGM.getModule().getDataLayout().getStructLayout(ST);
+ };
+
+ auto ST = cast<StructType>(Ptr->getType()->getPointerElementType());
+ auto SL = GetStructLayout(ST);
+ auto R = cast<CXXRecordDecl>(Ty->getAsRecordDecl());
+ const ASTRecordLayout &ASTLayout = CGF.getContext().getASTRecordLayout(R);
+ size_t RunningOffset = 0;
+ for (auto Base : R->bases()) {
+ // Zero padding between base elements.
+ auto BaseRecord = cast<CXXRecordDecl>(Base.getType()->getAsRecordDecl());
+ auto Offset = static_cast<size_t>(
+ ASTLayout.getBaseClassOffset(BaseRecord).getQuantity());
+ for (; RunningOffset < Offset; ++RunningOffset) {
+ WriteZeroAtOffset(RunningOffset);
+ }
+ // Recursively zero out base classes.
+ auto Index = SL->getElementContainingOffset(Offset);
+ auto BaseElement = CGF.Builder.CreateStructGEP(Ptr, Index);
+ RecursivelyZeroNonValueBits(CGF, BaseElement, Base.getType());
+ // Use the LLVM StructType data layout so we pick up on packed types.
+ auto SL = GetStructLayout(ST->getElementType(Index));
+ auto Size = SL->getSizeInBytes();
+ RunningOffset = Offset + Size;
+ }
+
+ size_t NumFeilds = std::distance(R->field_begin(), R->field_end());
+ auto CurrentField = R->field_begin();
+ for (size_t I = 0; I < NumFeilds; ++I, ++CurrentField) {
+ // Size needs to be in bytes so we can compare it later.
+ auto Offset = ASTLayout.getFieldOffset(I) / 8;
+ for (; RunningOffset < Offset; ++RunningOffset) {
+ WriteZeroAtOffset(RunningOffset);
+ }
+
+ auto Index = SL->getElementContainingOffset(Offset);
+ // If this field is an object, it may have non-zero padding.
+ if (CurrentField->getType()->isRecordType()) {
+ auto Element = CGF.Builder.CreateStructGEP(Ptr, Index);
+ RecursivelyZeroNonValueBits(CGF, Element, CurrentField->getType());
+ }
+
+ auto Size = CGF.CGM.getModule().getDataLayout()
+ .getTypeSizeInBits(ST->getElementType(Index))
+ .getKnownMinSize() / 8;
+ RunningOffset = Offset + Size;
+ }
+ // Clear all bits after the last field.
+ auto Size = SL->getSizeInBytes();
+ for (; RunningOffset < Size; ++RunningOffset) {
+ WriteZeroAtOffset(RunningOffset);
+ }
+}
+
RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
const CallExpr *E,
ReturnValueSlot ReturnValue) {
@@ -2946,6 +3011,13 @@
return RValue::get(Ptr);
}
+ case Builtin::BI__builtin_zero_non_value_bits: {
+ const Expr *Op = E->getArg(0);
+ Value *Address = EmitScalarExpr(Op);
+ auto PointeeTy = Op->getType()->getPointeeType();
+ RecursivelyZeroNonValueBits(*this, Address, PointeeTy);
+ return RValue::get(nullptr);
+ }
case Builtin::BI__sync_fetch_and_add:
case Builtin::BI__sync_fetch_and_sub:
case Builtin::BI__sync_fetch_and_or:
Index: clang/include/clang/Basic/Builtins.def
===================================================================
--- clang/include/clang/Basic/Builtins.def
+++ clang/include/clang/Basic/Builtins.def
@@ -534,6 +534,7 @@
BUILTIN(__builtin_thread_pointer, "v*", "nc")
BUILTIN(__builtin_launder, "v*v*", "nt")
LANGBUILTIN(__builtin_is_constant_evaluated, "b", "n", CXX_LANG)
+LANGBUILTIN(__builtin_zero_non_value_bits, "v.", "n", CXX_LANG)
// GCC exception builtins
BUILTIN(__builtin_eh_return, "vzv*", "r") // FIXME: Takes intptr_t, not size_t!
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