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GCC has gained support for these multiprecision arithmetic builtins in
[`r14-1896-g2b4e0415ad6`](https://gcc.gnu.org/g:2b4e0415ad6), and although they
aren't explicitly specified
as such in the documentation, they are usable in a constexpr context.
This commit adds constexpr evaluation support to Clang to match GCC's
behavior. The implementation mirrors how the builtins are lowered to a
pair of `u{add,sub}.with.overflow` operations and the carryout is set to
1 if either of those result in an overflow.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D156156
Files:
clang/include/clang/Basic/Builtins.def
clang/lib/AST/ExprConstant.cpp
clang/test/SemaCXX/builtins-multiprecision.cpp
Index: clang/test/SemaCXX/builtins-multiprecision.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/builtins-multiprecision.cpp
@@ -0,0 +1,105 @@
+// RUN: %clang_cc1 -fsyntax-only -std=c++17 -verify %s
+// expected-no-diagnostics
+
+#include <limits.h>
+
+template<typename T>
+struct Result {
+ T value;
+ T carry;
+ constexpr bool operator==(const Result<T> &Other) {
+ return value == Other.value && carry == Other.carry;
+ }
+};
+
+template<typename T>
+constexpr Result<T> add(T Lhs, T Rhs, T Carryin)
+{
+ T Carryout = 0;
+ if constexpr(__is_same(T, unsigned char))
+ return { __builtin_addcb(Lhs, Rhs, Carryin, &Carryout), Carryout };
+ else if constexpr(__is_same(T, unsigned short))
+ return { __builtin_addcs(Lhs, Rhs, Carryin, &Carryout), Carryout };
+ else if constexpr(__is_same(T, unsigned int))
+ return { __builtin_addc(Lhs, Rhs, Carryin, &Carryout), Carryout };
+ else if constexpr(__is_same(T, unsigned long))
+ return { __builtin_addcl(Lhs, Rhs, Carryin, &Carryout), Carryout };
+ else if constexpr(__is_same(T, unsigned long long))
+ return { __builtin_addcll(Lhs, Rhs, Carryin, &Carryout), Carryout };
+}
+
+static_assert(add<unsigned char>(0, 0, 0) == Result<unsigned char>{0, 0});
+static_assert(add<unsigned char>(0, 0, 1) == Result<unsigned char>{1, 0});
+static_assert(add<unsigned char>(UCHAR_MAX - 1, 1, 1) == Result<unsigned char>{0, 1});
+static_assert(add<unsigned char>(UCHAR_MAX, 1, 0) == Result<unsigned char>{0, 1});
+static_assert(add<unsigned char>(UCHAR_MAX, 1, 1) == Result<unsigned char>{1, 1});
+
+static_assert(add<unsigned short>(0, 0, 0) == Result<unsigned short>{0, 0});
+static_assert(add<unsigned short>(0, 0, 1) == Result<unsigned short>{1, 0});
+static_assert(add<unsigned short>(USHRT_MAX - 1, 1, 1) == Result<unsigned short>{0, 1});
+static_assert(add<unsigned short>(USHRT_MAX, 1, 0) == Result<unsigned short>{0, 1});
+static_assert(add<unsigned short>(USHRT_MAX, 1, 1) == Result<unsigned short>{1, 1});
+
+static_assert(add<unsigned int>(0, 0, 0) == Result<unsigned int>{0, 0});
+static_assert(add<unsigned int>(0, 0, 1) == Result<unsigned int>{1, 0});
+static_assert(add<unsigned int>(UINT_MAX - 1, 1, 1) == Result<unsigned int>{0, 1});
+static_assert(add<unsigned int>(UINT_MAX, 1, 0) == Result<unsigned int>{0, 1});
+static_assert(add<unsigned int>(UINT_MAX, 1, 1) == Result<unsigned int>{1, 1});
+
+static_assert(add<unsigned long>(0, 0, 0) == Result<unsigned long>{0, 0});
+static_assert(add<unsigned long>(0, 0, 1) == Result<unsigned long>{1, 0});
+static_assert(add<unsigned long>(ULONG_MAX - 1, 1, 1) == Result<unsigned long>{0, 1});
+static_assert(add<unsigned long>(ULONG_MAX, 1, 0) == Result<unsigned long>{0, 1});
+static_assert(add<unsigned long>(ULONG_MAX, 1, 1) == Result<unsigned long>{1, 1});
+
+static_assert(add<unsigned long long>(0, 0, 0) == Result<unsigned long long>{0, 0});
+static_assert(add<unsigned long long>(0, 0, 1) == Result<unsigned long long>{1, 0});
+static_assert(add<unsigned long long>(ULLONG_MAX - 1, 1, 1) == Result<unsigned long long>{0, 1});
+static_assert(add<unsigned long long>(ULLONG_MAX, 1, 0) == Result<unsigned long long>{0, 1});
+static_assert(add<unsigned long long>(ULLONG_MAX, 1, 1) == Result<unsigned long long>{1, 1});
+
+template<typename T>
+constexpr Result<T> sub(T Lhs, T Rhs, T Carryin)
+{
+ T Carryout = 0;
+ if constexpr(__is_same(T, unsigned char))
+ return { __builtin_subcb(Lhs, Rhs, Carryin, &Carryout), Carryout };
+ else if constexpr(__is_same(T, unsigned short))
+ return { __builtin_subcs(Lhs, Rhs, Carryin, &Carryout), Carryout };
+ else if constexpr(__is_same(T, unsigned int))
+ return { __builtin_subc(Lhs, Rhs, Carryin, &Carryout), Carryout };
+ else if constexpr(__is_same(T, unsigned long))
+ return { __builtin_subcl(Lhs, Rhs, Carryin, &Carryout), Carryout };
+ else if constexpr(__is_same(T, unsigned long long))
+ return { __builtin_subcll(Lhs, Rhs, Carryin, &Carryout), Carryout };
+}
+
+static_assert(sub<unsigned char>(0, 0, 0) == Result<unsigned char>{0, 0});
+static_assert(sub<unsigned char>(0, 0, 1) == Result<unsigned char>{UCHAR_MAX, 1});
+static_assert(sub<unsigned char>(0, 1, 0) == Result<unsigned char>{UCHAR_MAX, 1});
+static_assert(sub<unsigned char>(0, 1, 1) == Result<unsigned char>{UCHAR_MAX - 1, 1});
+static_assert(sub<unsigned char>(1, 0, 0) == Result<unsigned char>{1, 0});
+
+static_assert(sub<unsigned short>(0, 0, 0) == Result<unsigned short>{0, 0});
+static_assert(sub<unsigned short>(0, 0, 1) == Result<unsigned short>{USHRT_MAX, 1});
+static_assert(sub<unsigned short>(0, 1, 0) == Result<unsigned short>{USHRT_MAX, 1});
+static_assert(sub<unsigned short>(0, 1, 1) == Result<unsigned short>{USHRT_MAX - 1, 1});
+static_assert(sub<unsigned short>(1, 0, 0) == Result<unsigned short>{1, 0});
+
+static_assert(sub<unsigned int>(0, 0, 0) == Result<unsigned int>{0, 0});
+static_assert(sub<unsigned int>(0, 0, 1) == Result<unsigned int>{UINT_MAX, 1});
+static_assert(sub<unsigned int>(0, 1, 0) == Result<unsigned int>{UINT_MAX, 1});
+static_assert(sub<unsigned int>(0, 1, 1) == Result<unsigned int>{UINT_MAX - 1, 1});
+static_assert(sub<unsigned int>(1, 0, 0) == Result<unsigned int>{1, 0});
+
+static_assert(sub<unsigned long>(0, 0, 0) == Result<unsigned long>{0, 0});
+static_assert(sub<unsigned long>(0, 0, 1) == Result<unsigned long>{ULONG_MAX, 1});
+static_assert(sub<unsigned long>(0, 1, 0) == Result<unsigned long>{ULONG_MAX, 1});
+static_assert(sub<unsigned long>(0, 1, 1) == Result<unsigned long>{ULONG_MAX - 1, 1});
+static_assert(sub<unsigned long>(1, 0, 0) == Result<unsigned long>{1, 0});
+
+static_assert(sub<unsigned long long>(0, 0, 0) == Result<unsigned long long>{0, 0});
+static_assert(sub<unsigned long long>(0, 0, 1) == Result<unsigned long long>{ULLONG_MAX, 1});
+static_assert(sub<unsigned long long>(0, 1, 0) == Result<unsigned long long>{ULLONG_MAX, 1});
+static_assert(sub<unsigned long long>(0, 1, 1) == Result<unsigned long long>{ULLONG_MAX - 1, 1});
+static_assert(sub<unsigned long long>(1, 0, 0) == Result<unsigned long long>{1, 0});
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -12551,6 +12551,56 @@
return false;
return Success(DidOverflow, E);
}
+ case Builtin::BI__builtin_addcb:
+ case Builtin::BI__builtin_addcs:
+ case Builtin::BI__builtin_addc:
+ case Builtin::BI__builtin_addcl:
+ case Builtin::BI__builtin_addcll:
+ case Builtin::BI__builtin_subcb:
+ case Builtin::BI__builtin_subcs:
+ case Builtin::BI__builtin_subc:
+ case Builtin::BI__builtin_subcl:
+ case Builtin::BI__builtin_subcll: {
+ APSInt X, Y, CarryIn;
+ LValue CarryOut;
+
+ QualType ResultType = E->getArg(3)->getType()->getPointeeType();
+ if (!EvaluateInteger(E->getArg(0), X, Info) ||
+ !EvaluateInteger(E->getArg(1), Y, Info) ||
+ !EvaluateInteger(E->getArg(2), CarryIn, Info) ||
+ !EvaluatePointer(E->getArg(3), CarryOut, Info))
+ return false;
+
+ APInt Result;
+ bool DidOverflow1 = false;
+ bool DidOverflow2 = false;
+
+ switch (BuiltinOp) {
+ default:
+ llvm_unreachable("Invalid value for BuiltinOp");
+ case Builtin::BI__builtin_addcb:
+ case Builtin::BI__builtin_addcs:
+ case Builtin::BI__builtin_addc:
+ case Builtin::BI__builtin_addcl:
+ case Builtin::BI__builtin_addcll:
+ Result = X.uadd_ov(Y, DidOverflow1).uadd_ov(CarryIn, DidOverflow2);
+ break;
+ case Builtin::BI__builtin_subcb:
+ case Builtin::BI__builtin_subcs:
+ case Builtin::BI__builtin_subc:
+ case Builtin::BI__builtin_subcl:
+ case Builtin::BI__builtin_subcll:
+ Result = X.usub_ov(Y, DidOverflow1).usub_ov(CarryIn, DidOverflow2);
+ break;
+ }
+
+ APSInt DidOverflow(
+ APInt(Result.getBitWidth(), DidOverflow1 || DidOverflow2));
+ APValue DidOverflowVal{DidOverflow};
+ if (!handleAssignment(Info, E, CarryOut, ResultType, DidOverflowVal))
+ return false;
+ return Success(Result, E);
+ }
}
}
Index: clang/include/clang/Basic/Builtins.def
===================================================================
--- clang/include/clang/Basic/Builtins.def
+++ clang/include/clang/Basic/Builtins.def
@@ -1611,16 +1611,16 @@
BUILTIN(__builtin_assume_separate_storage, "vvCD*vCD*", "nE")
// Multiprecision Arithmetic Builtins.
-BUILTIN(__builtin_addcb, "UcUcCUcCUcCUc*", "n")
-BUILTIN(__builtin_addcs, "UsUsCUsCUsCUs*", "n")
-BUILTIN(__builtin_addc, "UiUiCUiCUiCUi*", "n")
-BUILTIN(__builtin_addcl, "ULiULiCULiCULiCULi*", "n")
-BUILTIN(__builtin_addcll, "ULLiULLiCULLiCULLiCULLi*", "n")
-BUILTIN(__builtin_subcb, "UcUcCUcCUcCUc*", "n")
-BUILTIN(__builtin_subcs, "UsUsCUsCUsCUs*", "n")
-BUILTIN(__builtin_subc, "UiUiCUiCUiCUi*", "n")
-BUILTIN(__builtin_subcl, "ULiULiCULiCULiCULi*", "n")
-BUILTIN(__builtin_subcll, "ULLiULLiCULLiCULLiCULLi*", "n")
+BUILTIN(__builtin_addcb, "UcUcCUcCUcCUc*", "nE")
+BUILTIN(__builtin_addcs, "UsUsCUsCUsCUs*", "nE")
+BUILTIN(__builtin_addc, "UiUiCUiCUiCUi*", "nE")
+BUILTIN(__builtin_addcl, "ULiULiCULiCULiCULi*", "nE")
+BUILTIN(__builtin_addcll, "ULLiULLiCULLiCULLiCULLi*", "nE")
+BUILTIN(__builtin_subcb, "UcUcCUcCUcCUc*", "nE")
+BUILTIN(__builtin_subcs, "UsUsCUsCUsCUs*", "nE")
+BUILTIN(__builtin_subc, "UiUiCUiCUiCUi*", "nE")
+BUILTIN(__builtin_subcl, "ULiULiCULiCULiCULi*", "nE")
+BUILTIN(__builtin_subcll, "ULLiULLiCULLiCULLiCULLi*", "nE")
// Checked Arithmetic Builtins for Security.
BUILTIN(__builtin_add_overflow, "b.", "ntE")
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