[Sema] -Wformat-pedantic only for NSInteger/NSUInteger %tu/%td on Darwin

The '%tu'/'%td' as formatting specifiers have been used to print out the
NSInteger/NSUInteger values for a long time. Typically their ABI matches, but that's
not the case on watchOS. The ABI difference boils down to the following:

- Regular 32-bit darwin targets (like armv7) use 'ptrdiff_t' of type 'int',
  which matches 'NSInteger'.
- WatchOS arm target (armv7k) uses 'ptrdiff_t' of type 'long', which doesn't
  match 'NSInteger' of type 'int'.

Because of this ABI difference these specifiers trigger -Wformat warnings only
for watchOS builds, which is really inconvenient for cross-platform code.

This patch avoids this -Wformat warning for '%tu'/'%td' and NS[U]Integer only,
and instead uses the new -Wformat-pedantic warning that JF introduced in
https://reviews.llvm.org/D47290. This is acceptable because Darwin guarantees that,
despite the watchOS ABI differences, sizeof(ptrdiff_t) == sizeof(NS[U]Integer),
and alignof(ptrdiff_t) == alignof(NS[U]Integer) so the warning is therefore noisy
for pedantic reasons.

I'll update public documentation to ensure that this behaviour is properly
communicated.

rdar://41739204

Differential Revision: https://reviews.llvm.org/D48852

llvm-svn: 336396

1 files changed, 3 insertions, 2 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 98aeb61fa75..cd2aabb8948 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -6894,10 +6894,11 @@ CheckPrintfHandler::checkFormatExpr(const analyze_printf::PrintfSpecifier &FS,
     QualType CastTy;
     std::tie(CastTy, CastTyName) = shouldNotPrintDirectly(S.Context, IntendedTy, E);
     if (!CastTy.isNull()) {
-      // %zi/%zu are OK to use for NSInteger/NSUInteger of type int
+      // %zi/%zu and %td/%tu are OK to use for NSInteger/NSUInteger of type int
       // (long in ASTContext). Only complain to pedants.
       if ((CastTyName == "NSInteger" || CastTyName == "NSUInteger") &&
-          AT.isSizeT() && AT.matchesType(S.Context, CastTy))
+          (AT.isSizeT() || AT.isPtrdiffT()) &&
+          AT.matchesType(S.Context, CastTy))
         Pedantic = true;
       IntendedTy = CastTy;
       ShouldNotPrintDirectly = true;