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[clang][ExprConst] Fix second arg of __builtin_{clzg,ctzg} not always being evaluated #86742

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Merged
merged 3 commits into from
Mar 29, 2024
Merged

[clang][ExprConst] Fix second arg of __builtin_{clzg,ctzg} not always being evaluated #86742

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c615f65
[clang][ExprConst] Fix second arg of __builtin_{clzg,ctzg} not always…
overmighty Mar 26, 2024
a0f9004
fixup! [clang][ExprConst] Fix second arg of __builtin_{clzg,ctzg} not…
overmighty Mar 26, 2024
951e8d2
fixup! [clang][ExprConst] Fix second arg of __builtin_{clzg,ctzg} not…
overmighty Mar 27, 2024
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30 changes: 20 additions & 10 deletions clang/lib/AST/ExprConstant.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -12361,12 +12361,17 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
if (!EvaluateInteger(E->getArg(0), Val, Info))
return false;

std::optional<APSInt> Fallback;
if (BuiltinOp == Builtin::BI__builtin_clzg && E->getNumArgs() > 1) {
APSInt FallbackTemp;
if (!EvaluateInteger(E->getArg(1), FallbackTemp, Info))
return false;
Fallback = FallbackTemp;
}

if (!Val) {
if (BuiltinOp == Builtin::BI__builtin_clzg && E->getNumArgs() > 1) {
if (!EvaluateInteger(E->getArg(1), Val, Info))
return false;
return Success(Val, E);
}
if (Fallback)
return Success(*Fallback, 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
Expand Down Expand Up @@ -12425,12 +12430,17 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
if (!EvaluateInteger(E->getArg(0), Val, Info))
return false;

std::optional<APSInt> Fallback;
if (BuiltinOp == Builtin::BI__builtin_ctzg && E->getNumArgs() > 1) {
APSInt FallbackTemp;
if (!EvaluateInteger(E->getArg(1), FallbackTemp, Info))
return false;
Fallback = FallbackTemp;
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I guess using a bool HasFallback instead of std::optional would be more efficient but defaulting to std::optional feels like better practice.

}

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

return Error(E);
}
Expand Down
34 changes: 34 additions & 0 deletions clang/test/Sema/constant-builtins-all-args-evaluated.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,34 @@
// RUN: %clang_cc1 -fsyntax-only -verify %s
// expected-no-diagnostics

constexpr int test_clzg_0() {
int x = 0;
(void)__builtin_clzg(0U, ++x);
return x;
}

static_assert(test_clzg_0() == 1);

constexpr int test_clzg_1() {
int x = 0;
(void)__builtin_clzg(1U, ++x);
return x;
}

static_assert(test_clzg_1() == 1);

constexpr int test_ctzg_0() {
int x = 0;
(void)__builtin_ctzg(0U, ++x);
return x;
}

static_assert(test_ctzg_0() == 1);

constexpr int test_ctzg_1() {
int x = 0;
(void)__builtin_ctzg(1U, ++x);
return x;
}

static_assert(test_ctzg_1() == 1);