[clang] [clang] constexpr built-in abs function. (PR #112539)
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Wed Oct 16 07:36:41 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: None (c8ef)
<details>
<summary>Changes</summary>
According to [P0533R9](https://wg21.link/P0533R9), the C++ standard library functions corresponding to the C macros in `[c.math.abs]` are now `constexpr`.
To implement this feature in libc++, we must make the built-in abs function `constexpr`. This patch adds the implementation of a `constexpr` abs function for the current constant evaluator and the new bytecode interpreter.
It is important to note that in 2's complement systems, the absolute value of the most negative value is out of range. In gcc, it will result in an out-of-range error and will not be evaluated as constants. We follow the same approach here.
---
Full diff: https://github.com/llvm/llvm-project/pull/112539.diff
6 Files Affected:
- (modified) clang/include/clang/Basic/Builtins.td (+1)
- (modified) clang/lib/AST/ByteCode/InterpBuiltin.cpp (+20)
- (modified) clang/lib/AST/ExprConstant.cpp (+13)
- (modified) clang/test/AST/ByteCode/builtin-functions.cpp (+9)
- (modified) clang/test/CodeGenCXX/builtins.cpp (+6-8)
- (modified) clang/test/Sema/constant-builtins-2.c (+12-1)
``````````diff
diff --git a/clang/include/clang/Basic/Builtins.td b/clang/include/clang/Basic/Builtins.td
index bda8a48be92bda..e1b4d5b1fdc0a5 100644
--- a/clang/include/clang/Basic/Builtins.td
+++ b/clang/include/clang/Basic/Builtins.td
@@ -2714,6 +2714,7 @@ def Abs : IntMathTemplate, LibBuiltin<"stdlib.h"> {
let Attributes = [NoThrow, Const];
let Prototype = "T(T)";
let AddBuiltinPrefixedAlias = 1;
+ let OnlyBuiltinPrefixedAliasIsConstexpr = 1;
}
def Calloc : LibBuiltin<"stdlib.h"> {
diff --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index 65c7b4e5306d72..b4ab744ea14104 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -563,6 +563,19 @@ static bool interp__builtin_fabs(InterpState &S, CodePtr OpPC,
return true;
}
+static bool interp__builtin_abs(InterpState &S, CodePtr OpPC,
+ const InterpFrame *Frame, const Function *Func,
+ const CallExpr *Call) {
+ PrimType ArgT = *S.getContext().classify(Call->getArg(0)->getType());
+ APSInt Val = peekToAPSInt(S.Stk, ArgT);
+ if (Val == APSInt(APSInt::getSignedMinValue(Val.getBitWidth()), false))
+ return false;
+ if (Val.isNegative())
+ Val.negate();
+ pushInteger(S, Val, Call->getType());
+ return true;
+}
+
static bool interp__builtin_popcount(InterpState &S, CodePtr OpPC,
const InterpFrame *Frame,
const Function *Func,
@@ -1808,6 +1821,13 @@ bool InterpretBuiltin(InterpState &S, CodePtr OpPC, const Function *F,
return false;
break;
+ case Builtin::BI__builtin_abs:
+ case Builtin::BI__builtin_labs:
+ case Builtin::BI__builtin_llabs:
+ if (!interp__builtin_abs(S, OpPC, Frame, F, Call))
+ return false;
+ break;
+
case Builtin::BI__builtin_popcount:
case Builtin::BI__builtin_popcountl:
case Builtin::BI__builtin_popcountll:
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 52a7f5778ce6d2..d1d6790e152527 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -13055,6 +13055,19 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
return Success(Val.popcount() % 2, E);
}
+ case Builtin::BI__builtin_abs:
+ case Builtin::BI__builtin_labs:
+ case Builtin::BI__builtin_llabs: {
+ APSInt Val;
+ if (!EvaluateInteger(E->getArg(0), Val, Info))
+ return false;
+ if (Val == APSInt(APSInt::getSignedMinValue(Val.getBitWidth()), false))
+ return false;
+ if (Val.isNegative())
+ Val.negate();
+ return Success(Val, E);
+ }
+
case Builtin::BI__builtin_popcount:
case Builtin::BI__builtin_popcountl:
case Builtin::BI__builtin_popcountll:
diff --git a/clang/test/AST/ByteCode/builtin-functions.cpp b/clang/test/AST/ByteCode/builtin-functions.cpp
index 450ff5671314db..1ec9b5fdcbd228 100644
--- a/clang/test/AST/ByteCode/builtin-functions.cpp
+++ b/clang/test/AST/ByteCode/builtin-functions.cpp
@@ -265,6 +265,15 @@ namespace fpclassify {
char classify_subnorm [__builtin_fpclassify(-1, -1, -1, +1, -1, 1.0e-38f)];
}
+namespace abs {
+static_assert(__builtin_abs(14) == 14, "");
+static_assert(__builtin_labs(14L) == 14L, "");
+static_assert(__builtin_llabs(14LL) == 14LL, "");
+static_assert(__builtin_abs(-14) == 14, "");
+static_assert(__builtin_labs(-0x14L) == 0x14L, "");
+static_assert(__builtin_llabs(-0x141414141414LL) == 0x141414141414LL, "");
+} // namespace abs
+
namespace fabs {
static_assert(__builtin_fabs(-14.0) == 14.0, "");
}
diff --git a/clang/test/CodeGenCXX/builtins.cpp b/clang/test/CodeGenCXX/builtins.cpp
index 90265186fb3d8c..37f9491d12d04b 100644
--- a/clang/test/CodeGenCXX/builtins.cpp
+++ b/clang/test/CodeGenCXX/builtins.cpp
@@ -14,6 +14,12 @@ int o = X::__builtin_fabs(-2.0);
long p = X::__builtin_fabsf(-3.0f);
// CHECK: @p ={{.*}} global i64 3, align 8
+int x = __builtin_abs(-2);
+// CHECK: @x ={{.*}} global i32 2, align 4
+
+long y = __builtin_abs(-2l);
+// CHECK: @y ={{.*}} global i64 2, align 8
+
// PR8839
extern "C" char memmove();
@@ -52,14 +58,6 @@ extern "C" int __builtin_abs(int); // #1
long __builtin_abs(long); // #2
extern "C" int __builtin_abs(int); // #3
-int x = __builtin_abs(-2);
-// CHECK: [[X:%.+]] = call i32 @llvm.abs.i32(i32 -2, i1 true)
-// CHECK-NEXT: store i32 [[X]], ptr @x, align 4
-
-long y = __builtin_abs(-2l);
-// CHECK: [[Y:%.+]] = call noundef i64 @_Z13__builtin_absl(i64 noundef -2)
-// CHECK: store i64 [[Y]], ptr @y, align 8
-
extern const char char_memchr_arg[32];
char *memchr_result = __builtin_char_memchr(char_memchr_arg, 123, 32);
// CHECK: call ptr @memchr(ptr noundef @char_memchr_arg, i32 noundef 123, i64 noundef 32)
diff --git a/clang/test/Sema/constant-builtins-2.c b/clang/test/Sema/constant-builtins-2.c
index da2264500d7680..e465a3c5f0ad86 100644
--- a/clang/test/Sema/constant-builtins-2.c
+++ b/clang/test/Sema/constant-builtins-2.c
@@ -35,7 +35,7 @@ long double g11 = __builtin_nansl("");
__float128 g11_2 = __builtin_nansf128("");
#endif
-//int g12 = __builtin_abs(-12);
+int g12 = __builtin_abs(-12);
double g13 = __builtin_fabs(-12.);
double g13_0 = __builtin_fabs(-0.);
@@ -456,6 +456,17 @@ char clrsb9[__builtin_clrsb(1 << (BITSIZE(int) - 1)) == 0 ? 1 : -1];
char clrsb10[__builtin_clrsb(~(1 << (BITSIZE(int) - 1))) == 0 ? 1 : -1];
char clrsb11[__builtin_clrsb(0xf) == BITSIZE(int) - 5 ? 1 : -1];
char clrsb12[__builtin_clrsb(~0x1f) == BITSIZE(int) - 6 ? 1 : -1];
+
+char abs1[__builtin_abs(-12)];
+char abs2[__builtin_labs(-12L)];
+char abs3[__builtin_llabs(-12LL)];
+int abs4 = __builtin_abs(1 << (BITSIZE(int) - 1)); // expected-error {{not a compile-time constant}}
+char abs5[__builtin_abs((1 << (BITSIZE(int) - 1)) + 1)];
+long abs6 = __builtin_labs(1L << (BITSIZE(long) - 1)); // expected-error {{not a compile-time constant}}
+long abs7 = __builtin_labs((1L << (BITSIZE(long) - 1)) + 1);
+long long abs8 = __builtin_llabs(1LL << (BITSIZE(long long) - 1)); // expected-error {{not a compile-time constant}}
+long long abs9 = __builtin_llabs((1LL << (BITSIZE(long long) - 1)) + 1);
+
#undef BITSIZE
// GCC misc stuff
``````````
</details>
https://github.com/llvm/llvm-project/pull/112539
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