Skip to content

[clang] Implement constexpr support for __builtin_{clzg,ctzg} #86577

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 3 commits into from
Mar 26, 2024
Merged

[clang] Implement constexpr support for __builtin_{clzg,ctzg} #86577

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
82bf133
[clang] Implement constexpr support for __builtin_{clzg,ctzg}
overmighty Mar 25, 2024
59bb4f2
fixup! [clang] Implement constexpr support for __builtin_{clzg,ctzg}
overmighty Mar 25, 2024
d3e2314
fixup! [clang] Implement constexpr support for __builtin_{clzg,ctzg}
overmighty Mar 25, 2024
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 2 additions & 0 deletions clang/docs/LanguageExtensions.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -5420,10 +5420,12 @@ The following builtin intrinsics can be used in constant expressions:
* ``__builtin_clzl``
* ``__builtin_clzll``
* ``__builtin_clzs``
* ``__builtin_clzg``
* ``__builtin_ctz``
* ``__builtin_ctzl``
* ``__builtin_ctzll``
* ``__builtin_ctzs``
* ``__builtin_ctzg``
* ``__builtin_ffs``
* ``__builtin_ffsl``
* ``__builtin_ffsll``
Expand Down
5 changes: 5 additions & 0 deletions clang/docs/ReleaseNotes.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,11 @@ Non-comprehensive list of changes in this release

- Lambda expressions are now accepted in C++03 mode as an extension.

- Added ``__builtin_clzg`` and ``__builtin_ctzg`` as type-generic alternatives
to ``__builtin_clz{,s,l,ll}`` and ``__builtin_ctz{,s,l,ll}`` respectively,
with support for any unsigned integer type. Like the previous builtins, these
Comment on lines +191 to +193
Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I had forgotten to add a release note for the addition of these builtins in #83431.

new builtins are constexpr and may be used in constant expressions.

New Compiler Flags
------------------

Expand Down
4 changes: 2 additions & 2 deletions clang/include/clang/Basic/Builtins.td
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -678,7 +678,7 @@ def Clz : Builtin, BitShort_Int_Long_LongLongTemplate {

def Clzg : Builtin {
let Spellings = ["__builtin_clzg"];
let Attributes = [NoThrow, Const, CustomTypeChecking];
let Attributes = [NoThrow, Const, Constexpr, CustomTypeChecking];
let Prototype = "int(...)";
}

Expand All @@ -690,7 +690,7 @@ def Ctz : Builtin, BitShort_Int_Long_LongLongTemplate {

def Ctzg : Builtin {
let Spellings = ["__builtin_ctzg"];
let Attributes = [NoThrow, Const, CustomTypeChecking];
let Attributes = [NoThrow, Const, Constexpr, CustomTypeChecking];
let Prototype = "int(...)";
}

Expand Down
37 changes: 28 additions & 9 deletions clang/lib/AST/ExprConstant.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -12354,21 +12354,31 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
case Builtin::BI__builtin_clzl:
case Builtin::BI__builtin_clzll:
case Builtin::BI__builtin_clzs:
case Builtin::BI__builtin_clzg:
case Builtin::BI__lzcnt16: // Microsoft variants of count leading-zeroes
case Builtin::BI__lzcnt:
case Builtin::BI__lzcnt64: {
APSInt Val;
if (!EvaluateInteger(E->getArg(0), Val, Info))
return false;

// When the argument is 0, the result of GCC builtins is undefined, whereas
// for Microsoft intrinsics, the result is the bit-width of the argument.
bool ZeroIsUndefined = BuiltinOp != Builtin::BI__lzcnt16 &&
BuiltinOp != Builtin::BI__lzcnt &&
BuiltinOp != Builtin::BI__lzcnt64;
if (!Val) {
if (BuiltinOp == Builtin::BI__builtin_clzg && E->getNumArgs() > 1) {
if (!EvaluateInteger(E->getArg(1), Val, Info))
Copy link
Collaborator

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This EvaluateInteger call can't be guarded by the if (!Val) check: even if we don't actually use the value of the second argument, we have to evaluate it for side-effects. We don't want short-circuit the evaluation like for &&/||.

Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Oops. I will fix this now.

return false;
return Success(Val, E);
}

if (ZeroIsUndefined && !Val)
return Error(E);
// When the argument is 0, the result of GCC builtins is undefined,
// whereas for Microsoft intrinsics, the result is the bit-width of the
// argument.
bool ZeroIsUndefined = BuiltinOp != Builtin::BI__lzcnt16 &&
BuiltinOp != Builtin::BI__lzcnt &&
BuiltinOp != Builtin::BI__lzcnt64;

if (ZeroIsUndefined)
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Sink the definition of ZeroIsUndefined closer to the use to reduce its scope. We might not need to evaluate that expression.

return Error(E);
}

return Success(Val.countl_zero(), E);
}
Expand Down Expand Up @@ -12410,12 +12420,21 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
case Builtin::BI__builtin_ctz:
case Builtin::BI__builtin_ctzl:
case Builtin::BI__builtin_ctzll:
case Builtin::BI__builtin_ctzs: {
case Builtin::BI__builtin_ctzs:
case Builtin::BI__builtin_ctzg: {
APSInt Val;
if (!EvaluateInteger(E->getArg(0), Val, Info))
return false;
if (!Val)

if (!Val) {
if (BuiltinOp == Builtin::BI__builtin_ctzg && E->getNumArgs() > 1) {
if (!EvaluateInteger(E->getArg(1), Val, Info))
return false;
return Success(Val, E);
}

return Error(E);
}

return Success(Val.countr_zero(), E);
}
Expand Down
116 changes: 116 additions & 0 deletions clang/test/Sema/constant-builtins-2.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -218,6 +218,64 @@ char clz6[__builtin_clzll(0xFFLL) == BITSIZE(long long) - 8 ? 1 : -1];
char clz7[__builtin_clzs(0x1) == BITSIZE(short) - 1 ? 1 : -1];
char clz8[__builtin_clzs(0xf) == BITSIZE(short) - 4 ? 1 : -1];
char clz9[__builtin_clzs(0xfff) == BITSIZE(short) - 12 ? 1 : -1];
int clz10 = __builtin_clzg((unsigned char)0); // expected-error {{not a compile-time constant}}
char clz11[__builtin_clzg((unsigned char)0, 42) == 42 ? 1 : -1];
char clz12[__builtin_clzg((unsigned char)0x1) == BITSIZE(char) - 1 ? 1 : -1];
char clz13[__builtin_clzg((unsigned char)0x1, 42) == BITSIZE(char) - 1 ? 1 : -1];
char clz14[__builtin_clzg((unsigned char)0xf) == BITSIZE(char) - 4 ? 1 : -1];
char clz15[__builtin_clzg((unsigned char)0xf, 42) == BITSIZE(char) - 4 ? 1 : -1];
char clz16[__builtin_clzg((unsigned char)(1 << (BITSIZE(char) - 1))) == 0 ? 1 : -1];
char clz17[__builtin_clzg((unsigned char)(1 << (BITSIZE(char) - 1)), 42) == 0 ? 1 : -1];
int clz18 = __builtin_clzg((unsigned short)0); // expected-error {{not a compile-time constant}}
char clz19[__builtin_clzg((unsigned short)0, 42) == 42 ? 1 : -1];
char clz20[__builtin_clzg((unsigned short)0x1) == BITSIZE(short) - 1 ? 1 : -1];
char clz21[__builtin_clzg((unsigned short)0x1, 42) == BITSIZE(short) - 1 ? 1 : -1];
char clz22[__builtin_clzg((unsigned short)0xf) == BITSIZE(short) - 4 ? 1 : -1];
char clz23[__builtin_clzg((unsigned short)0xf, 42) == BITSIZE(short) - 4 ? 1 : -1];
char clz24[__builtin_clzg((unsigned short)(1 << (BITSIZE(short) - 1))) == 0 ? 1 : -1];
char clz25[__builtin_clzg((unsigned short)(1 << (BITSIZE(short) - 1)), 42) == 0 ? 1 : -1];
int clz26 = __builtin_clzg(0U); // expected-error {{not a compile-time constant}}
char clz27[__builtin_clzg(0U, 42) == 42 ? 1 : -1];
char clz28[__builtin_clzg(0x1U) == BITSIZE(int) - 1 ? 1 : -1];
char clz29[__builtin_clzg(0x1U, 42) == BITSIZE(int) - 1 ? 1 : -1];
char clz30[__builtin_clzg(0xfU) == BITSIZE(int) - 4 ? 1 : -1];
char clz31[__builtin_clzg(0xfU, 42) == BITSIZE(int) - 4 ? 1 : -1];
char clz32[__builtin_clzg(1U << (BITSIZE(int) - 1)) == 0 ? 1 : -1];
char clz33[__builtin_clzg(1U << (BITSIZE(int) - 1), 42) == 0 ? 1 : -1];
int clz34 = __builtin_clzg(0UL); // expected-error {{not a compile-time constant}}
char clz35[__builtin_clzg(0UL, 42) == 42 ? 1 : -1];
char clz36[__builtin_clzg(0x1UL) == BITSIZE(long) - 1 ? 1 : -1];
char clz37[__builtin_clzg(0x1UL, 42) == BITSIZE(long) - 1 ? 1 : -1];
char clz38[__builtin_clzg(0xfUL) == BITSIZE(long) - 4 ? 1 : -1];
char clz39[__builtin_clzg(0xfUL, 42) == BITSIZE(long) - 4 ? 1 : -1];
char clz40[__builtin_clzg(1UL << (BITSIZE(long) - 1)) == 0 ? 1 : -1];
char clz41[__builtin_clzg(1UL << (BITSIZE(long) - 1), 42) == 0 ? 1 : -1];
int clz42 = __builtin_clzg(0ULL); // expected-error {{not a compile-time constant}}
char clz43[__builtin_clzg(0ULL, 42) == 42 ? 1 : -1];
char clz44[__builtin_clzg(0x1ULL) == BITSIZE(long long) - 1 ? 1 : -1];
char clz45[__builtin_clzg(0x1ULL, 42) == BITSIZE(long long) - 1 ? 1 : -1];
char clz46[__builtin_clzg(0xfULL) == BITSIZE(long long) - 4 ? 1 : -1];
char clz47[__builtin_clzg(0xfULL, 42) == BITSIZE(long long) - 4 ? 1 : -1];
char clz48[__builtin_clzg(1ULL << (BITSIZE(long long) - 1)) == 0 ? 1 : -1];
char clz49[__builtin_clzg(1ULL << (BITSIZE(long long) - 1), 42) == 0 ? 1 : -1];
#ifdef __SIZEOF_INT128__
int clz50 = __builtin_clzg((unsigned __int128)0); // expected-error {{not a compile-time constant}}
char clz51[__builtin_clzg((unsigned __int128)0, 42) == 42 ? 1 : -1];
char clz52[__builtin_clzg((unsigned __int128)0x1) == BITSIZE(__int128) - 1 ? 1 : -1];
char clz53[__builtin_clzg((unsigned __int128)0x1, 42) == BITSIZE(__int128) - 1 ? 1 : -1];
char clz54[__builtin_clzg((unsigned __int128)0xf) == BITSIZE(__int128) - 4 ? 1 : -1];
char clz55[__builtin_clzg((unsigned __int128)0xf, 42) == BITSIZE(__int128) - 4 ? 1 : -1];
char clz56[__builtin_clzg((unsigned __int128)(1 << (BITSIZE(__int128) - 1))) == 0 ? 1 : -1];
char clz57[__builtin_clzg((unsigned __int128)(1 << (BITSIZE(__int128) - 1)), 42) == 0 ? 1 : -1];
#endif
int clz58 = __builtin_clzg((unsigned _BitInt(128))0); // expected-error {{not a compile-time constant}}
char clz59[__builtin_clzg((unsigned _BitInt(128))0, 42) == 42 ? 1 : -1];
char clz60[__builtin_clzg((unsigned _BitInt(128))0x1) == BITSIZE(_BitInt(128)) - 1 ? 1 : -1];
char clz61[__builtin_clzg((unsigned _BitInt(128))0x1, 42) == BITSIZE(_BitInt(128)) - 1 ? 1 : -1];
char clz62[__builtin_clzg((unsigned _BitInt(128))0xf) == BITSIZE(_BitInt(128)) - 4 ? 1 : -1];
char clz63[__builtin_clzg((unsigned _BitInt(128))0xf, 42) == BITSIZE(_BitInt(128)) - 4 ? 1 : -1];
char clz64[__builtin_clzg((unsigned _BitInt(128))(1 << (BITSIZE(_BitInt(128)) - 1))) == 0 ? 1 : -1];
char clz65[__builtin_clzg((unsigned _BitInt(128))(1 << (BITSIZE(_BitInt(128)) - 1)), 42) == 0 ? 1 : -1];

char ctz1[__builtin_ctz(1) == 0 ? 1 : -1];
char ctz2[__builtin_ctz(8) == 3 ? 1 : -1];
Expand All @@ -226,6 +284,64 @@ int ctz4 = __builtin_ctz(0); // expected-error {{not a compile-time constant}}
char ctz5[__builtin_ctzl(0x10L) == 4 ? 1 : -1];
char ctz6[__builtin_ctzll(0x100LL) == 8 ? 1 : -1];
char ctz7[__builtin_ctzs(1 << (BITSIZE(short) - 1)) == BITSIZE(short) - 1 ? 1 : -1];
int ctz8 = __builtin_ctzg((unsigned char)0); // expected-error {{not a compile-time constant}}
char ctz9[__builtin_ctzg((unsigned char)0, 42) == 42 ? 1 : -1];
char ctz10[__builtin_ctzg((unsigned char)0x1) == 0 ? 1 : -1];
char ctz11[__builtin_ctzg((unsigned char)0x1, 42) == 0 ? 1 : -1];
char ctz12[__builtin_ctzg((unsigned char)0x10) == 4 ? 1 : -1];
char ctz13[__builtin_ctzg((unsigned char)0x10, 42) == 4 ? 1 : -1];
char ctz14[__builtin_ctzg((unsigned char)(1 << (BITSIZE(char) - 1))) == BITSIZE(char) - 1 ? 1 : -1];
char ctz15[__builtin_ctzg((unsigned char)(1 << (BITSIZE(char) - 1)), 42) == BITSIZE(char) - 1 ? 1 : -1];
int ctz16 = __builtin_ctzg((unsigned short)0); // expected-error {{not a compile-time constant}}
char ctz17[__builtin_ctzg((unsigned short)0, 42) == 42 ? 1 : -1];
char ctz18[__builtin_ctzg((unsigned short)0x1) == 0 ? 1 : -1];
char ctz19[__builtin_ctzg((unsigned short)0x1, 42) == 0 ? 1 : -1];
char ctz20[__builtin_ctzg((unsigned short)0x10) == 4 ? 1 : -1];
char ctz21[__builtin_ctzg((unsigned short)0x10, 42) == 4 ? 1 : -1];
char ctz22[__builtin_ctzg((unsigned short)(1 << (BITSIZE(short) - 1))) == BITSIZE(short) - 1 ? 1 : -1];
char ctz23[__builtin_ctzg((unsigned short)(1 << (BITSIZE(short) - 1)), 42) == BITSIZE(short) - 1 ? 1 : -1];
int ctz24 = __builtin_ctzg(0U); // expected-error {{not a compile-time constant}}
char ctz25[__builtin_ctzg(0U, 42) == 42 ? 1 : -1];
char ctz26[__builtin_ctzg(0x1U) == 0 ? 1 : -1];
char ctz27[__builtin_ctzg(0x1U, 42) == 0 ? 1 : -1];
char ctz28[__builtin_ctzg(0x10U) == 4 ? 1 : -1];
char ctz29[__builtin_ctzg(0x10U, 42) == 4 ? 1 : -1];
char ctz30[__builtin_ctzg(1U << (BITSIZE(int) - 1)) == BITSIZE(int) - 1 ? 1 : -1];
char ctz31[__builtin_ctzg(1U << (BITSIZE(int) - 1), 42) == BITSIZE(int) - 1 ? 1 : -1];
int ctz32 = __builtin_ctzg(0UL); // expected-error {{not a compile-time constant}}
char ctz33[__builtin_ctzg(0UL, 42) == 42 ? 1 : -1];
char ctz34[__builtin_ctzg(0x1UL) == 0 ? 1 : -1];
char ctz35[__builtin_ctzg(0x1UL, 42) == 0 ? 1 : -1];
char ctz36[__builtin_ctzg(0x10UL) == 4 ? 1 : -1];
char ctz37[__builtin_ctzg(0x10UL, 42) == 4 ? 1 : -1];
char ctz38[__builtin_ctzg(1UL << (BITSIZE(long) - 1)) == BITSIZE(long) - 1 ? 1 : -1];
char ctz39[__builtin_ctzg(1UL << (BITSIZE(long) - 1), 42) == BITSIZE(long) - 1 ? 1 : -1];
int ctz40 = __builtin_ctzg(0ULL); // expected-error {{not a compile-time constant}}
char ctz41[__builtin_ctzg(0ULL, 42) == 42 ? 1 : -1];
char ctz42[__builtin_ctzg(0x1ULL) == 0 ? 1 : -1];
char ctz43[__builtin_ctzg(0x1ULL, 42) == 0 ? 1 : -1];
char ctz44[__builtin_ctzg(0x10ULL) == 4 ? 1 : -1];
char ctz45[__builtin_ctzg(0x10ULL, 42) == 4 ? 1 : -1];
char ctz46[__builtin_ctzg(1ULL << (BITSIZE(long long) - 1)) == BITSIZE(long long) - 1 ? 1 : -1];
char ctz47[__builtin_ctzg(1ULL << (BITSIZE(long long) - 1), 42) == BITSIZE(long long) - 1 ? 1 : -1];
#ifdef __SIZEOF_INT128__
int ctz48 = __builtin_ctzg((unsigned __int128)0); // expected-error {{not a compile-time constant}}
char ctz49[__builtin_ctzg((unsigned __int128)0, 42) == 42 ? 1 : -1];
char ctz50[__builtin_ctzg((unsigned __int128)0x1) == 0 ? 1 : -1];
char ctz51[__builtin_ctzg((unsigned __int128)0x1, 42) == 0 ? 1 : -1];
char ctz52[__builtin_ctzg((unsigned __int128)0x10) == 4 ? 1 : -1];
char ctz53[__builtin_ctzg((unsigned __int128)0x10, 42) == 4 ? 1 : -1];
char ctz54[__builtin_ctzg((unsigned __int128)1 << (BITSIZE(__int128) - 1)) == BITSIZE(__int128) - 1 ? 1 : -1];
char ctz55[__builtin_ctzg((unsigned __int128)1 << (BITSIZE(__int128) - 1), 42) == BITSIZE(__int128) - 1 ? 1 : -1];
#endif
int ctz56 = __builtin_ctzg((unsigned _BitInt(128))0); // expected-error {{not a compile-time constant}}
char ctz57[__builtin_ctzg((unsigned _BitInt(128))0, 42) == 42 ? 1 : -1];
char ctz58[__builtin_ctzg((unsigned _BitInt(128))0x1) == 0 ? 1 : -1];
char ctz59[__builtin_ctzg((unsigned _BitInt(128))0x1, 42) == 0 ? 1 : -1];
char ctz60[__builtin_ctzg((unsigned _BitInt(128))0x10) == 4 ? 1 : -1];
char ctz61[__builtin_ctzg((unsigned _BitInt(128))0x10, 42) == 4 ? 1 : -1];
char ctz62[__builtin_ctzg((unsigned _BitInt(128))1 << (BITSIZE(_BitInt(128)) - 1)) == BITSIZE(_BitInt(128)) - 1 ? 1 : -1];
char ctz63[__builtin_ctzg((unsigned _BitInt(128))1 << (BITSIZE(_BitInt(128)) - 1), 42) == BITSIZE(_BitInt(128)) - 1 ? 1 : -1];

char popcount1[__builtin_popcount(0) == 0 ? 1 : -1];
char popcount2[__builtin_popcount(0xF0F0) == 8 ? 1 : -1];
Expand Down