Index: lib/Sema/SemaChecking.cpp =================================================================== --- lib/Sema/SemaChecking.cpp +++ lib/Sema/SemaChecking.cpp @@ -7697,6 +7697,24 @@ return std::make_pair(QualType(), StringRef()); } +/// Return true if \p ICE is an implicit argument promotion of an arithmetic +/// type. Bit-field 'promotions' from a higher ranked type to a lower ranked +/// type do not count. +static bool +isArithmeticArgumentPromotion(Sema &S, const ImplicitCastExpr *ICE) { + QualType From = ICE->getSubExpr()->getType(); + QualType To = ICE->getType(); + // It's a floating promotion if the source type is a lower rank. + if (ICE->getCastKind() == CK_FloatingCast && + S.Context.getFloatingTypeOrder(From, To) < 0) + return true; + // It's an integer promotion if the destination type is the promoted + // source type. + return ICE->getCastKind() == CK_IntegralCast && + From->isPromotableIntegerType() && + S.Context.getPromotedIntegerType(From) == To; +} + bool CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS, const char *StartSpecifier, @@ -7724,11 +7742,11 @@ // Look through argument promotions for our error message's reported type. // This includes the integral and floating promotions, but excludes array - // and function pointer decay; seeing that an argument intended to be a - // string has type 'char [6]' is probably more confusing than 'char *'. + // and function pointer decay (seeing that an argument intended to be a + // string has type 'char [6]' is probably more confusing than 'char *') and + // certain bitfield promotions (bitfields can be 'demoted' to a lesser type). if (const ImplicitCastExpr *ICE = dyn_cast(E)) { - if (ICE->getCastKind() == CK_IntegralCast || - ICE->getCastKind() == CK_FloatingCast) { + if (isArithmeticArgumentPromotion(S, ICE)) { E = ICE->getSubExpr(); ExprTy = E->getType(); Index: test/Sema/format-strings-bitfield-promotion.c =================================================================== --- /dev/null +++ test/Sema/format-strings-bitfield-promotion.c @@ -0,0 +1,17 @@ +// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fsyntax-only -verify %s + +int printf(const char *restrict, ...); + +struct bitfields { + long a : 2; + unsigned long b : 2; + long c : 32; // assumes that int is 32 bits + unsigned long d : 32; // assumes that int is 32 bits +} bf; + +void bitfield_promotion() { + printf("%ld", bf.a); // expected-warning {{format specifies type 'long' but the argument has type 'int'}} + printf("%lu", bf.b); // expected-warning {{format specifies type 'unsigned long' but the argument has type 'int'}} + printf("%ld", bf.c); // expected-warning {{format specifies type 'long' but the argument has type 'int'}} + printf("%lu", bf.d); // expected-warning {{format specifies type 'unsigned long' but the argument has type 'unsigned int'}} +}