Explicitly permit undefined behavior in constant initializers for global
variables in C, in the cases where we can constant-fold it to a value
regardless (such as floating-point division by zero and signed integer
overflow). Strictly enforcing this rule breaks too much code.
llvm-svn: 254992
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 33ea76e..9996546 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -2891,7 +2891,10 @@
return cast<CXXDefaultInitExpr>(this)->getExpr()
->isConstantInitializer(Ctx, false, Culprit);
}
- if (isEvaluatable(Ctx))
+ // Allow certain forms of UB in constant initializers: signed integer
+ // overflow and floating-point division by zero. We'll give a warning on
+ // these, but they're common enough that we have to accept them.
+ if (isEvaluatable(Ctx, SE_AllowUndefinedBehavior))
return true;
if (Culprit)
*Culprit = this;
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index ffaf742..3c8868c 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -715,6 +715,32 @@
return keepEvaluatingAfterSideEffect();
}
+ /// Should we continue evaluation after encountering undefined behavior?
+ bool keepEvaluatingAfterUndefinedBehavior() {
+ switch (EvalMode) {
+ case EM_EvaluateForOverflow:
+ case EM_IgnoreSideEffects:
+ case EM_ConstantFold:
+ case EM_DesignatorFold:
+ return true;
+
+ case EM_PotentialConstantExpression:
+ case EM_PotentialConstantExpressionUnevaluated:
+ case EM_ConstantExpression:
+ case EM_ConstantExpressionUnevaluated:
+ return false;
+ }
+ llvm_unreachable("Missed EvalMode case");
+ }
+
+ /// Note that we hit something that was technically undefined behavior, but
+ /// that we can evaluate past it (such as signed overflow or floating-point
+ /// division by zero.)
+ bool noteUndefinedBehavior() {
+ EvalStatus.HasUndefinedBehavior = true;
+ return keepEvaluatingAfterUndefinedBehavior();
+ }
+
/// Should we continue evaluation as much as possible after encountering a
/// construct which can't be reduced to a value?
bool keepEvaluatingAfterFailure() {
@@ -1549,7 +1575,7 @@
const T &SrcValue, QualType DestType) {
Info.CCEDiag(E, diag::note_constexpr_overflow)
<< SrcValue << DestType;
- return Info.noteSideEffect();
+ return Info.noteUndefinedBehavior();
}
static bool HandleFloatToIntCast(EvalInfo &Info, const Expr *E,
@@ -1818,8 +1844,7 @@
if (LHS.isInfinity() || LHS.isNaN()) {
Info.CCEDiag(E, diag::note_constexpr_float_arithmetic) << LHS.isNaN();
- // Undefined behavior is a side-effect.
- return Info.noteSideEffect();
+ return Info.noteUndefinedBehavior();
}
return true;
}
@@ -8835,6 +8860,12 @@
HandleConversionToBool(Scratch.Val, Result);
}
+static bool hasUnacceptableSideEffect(Expr::EvalStatus &Result,
+ Expr::SideEffectsKind SEK) {
+ return (SEK < Expr::SE_AllowSideEffects && Result.HasSideEffects) ||
+ (SEK < Expr::SE_AllowUndefinedBehavior && Result.HasUndefinedBehavior);
+}
+
bool Expr::EvaluateAsInt(APSInt &Result, const ASTContext &Ctx,
SideEffectsKind AllowSideEffects) const {
if (!getType()->isIntegralOrEnumerationType())
@@ -8842,7 +8873,7 @@
EvalResult ExprResult;
if (!EvaluateAsRValue(ExprResult, Ctx) || !ExprResult.Val.isInt() ||
- (!AllowSideEffects && ExprResult.HasSideEffects))
+ hasUnacceptableSideEffect(ExprResult, AllowSideEffects))
return false;
Result = ExprResult.Val.getInt();
@@ -8905,9 +8936,10 @@
/// isEvaluatable - Call EvaluateAsRValue to see if this expression can be
/// constant folded, but discard the result.
-bool Expr::isEvaluatable(const ASTContext &Ctx) const {
+bool Expr::isEvaluatable(const ASTContext &Ctx, SideEffectsKind SEK) const {
EvalResult Result;
- return EvaluateAsRValue(Result, Ctx) && !Result.HasSideEffects;
+ return EvaluateAsRValue(Result, Ctx) &&
+ !hasUnacceptableSideEffect(Result, SEK);
}
APSInt Expr::EvaluateKnownConstInt(const ASTContext &Ctx,