// Random Notes
//===---------------------------------------------------------------------===//
-C90/C99/C++ Comparisons:
-http://david.tribble.com/text/cdiffs.htm
-
-//===---------------------------------------------------------------------===//
-Extensions:
-
- * "#define_target X Y"
- This preprocessor directive works exactly the same was as #define, but it
- notes that 'X' is a target-specific preprocessor directive. When used, a
- diagnostic is emitted indicating that the translation unit is non-portable.
-
- If a target-define is #undef'd before use, no diagnostic is emitted. If 'X'
- were previously a normal #define macro, the macro is tainted. If 'X' is
- subsequently #defined as a non-target-specific define, the taint bit is
- cleared.
-
- * "#define_other_target X"
- The preprocessor directive takes a single identifier argument. It notes
- that this identifier is a target-specific #define for some target other than
- the current one. Use of this identifier will result in a diagnostic.
-
- If 'X' is later #undef'd or #define'd, the taint bit is cleared. If 'X' is
- already defined, X is marked as a target-specific define.
-
-//===---------------------------------------------------------------------===//
-
-When we go to reimplement <tgmath.h>, we should do it more intelligently than
-the GCC-supplied header. EDG has an interesting __generic builtin that provides
-overloading for C:
-http://www.edg.com/docs/edg_cpp.pdf
-
-For example, they have:
- #define sin(x) __generic(x,,, sin, sinf, sinl, csin, csinf,csinl)(x)
-
-It's unclear to me why you couldn't just have a builtin like:
- __builtin_overload(1, arg1, impl1, impl2, impl3)
- __builtin_overload(2, arg1, arg2, impl1, impl2, impl3)
- __builtin_overload(3, arg1, arg2, arg3, impl1, impl2, impl3)
-
-Where the compiler would just pick the right "impl" based on the arguments
-provided. One nasty detail is that some arithmetic promotions most be done for
-use by the tgmath.h stuff, but it would be nice to be able to handle vectors
-etc as well without huge globs of macros. With the above scheme, you could
-use:
-
- #define sin(x) __builtin_overload(1, x, sin, sinf, sinl, csin, csinf,csinl)(x)
-
-and not need to keep track of which argument to "__generic" corresponds to which
-type, etc.
-
//===---------------------------------------------------------------------===//
To time GCC preprocessing speed without output, use:
"time gcc -MM file"
This is similar to -Eonly.
+//===---------------------------------------------------------------------===//
+
+Creating and using a PTH file for performance measurement (use a release build).
+
+$ clang -ccc-pch-is-pth -x objective-c-header INPUTS/Cocoa_h.m -o /tmp/tokencache
+$ clang -cc1 -token-cache /tmp/tokencache INPUTS/Cocoa_h.m
//===---------------------------------------------------------------------===//
3. File UIDs are created on request, not when files are opened.
These changes make it possible to efficiently have FileEntry objects for
files that exist on the file system, but have not been used yet.
-
+
Once this is done:
1. DirectoryEntry gets a boolean value "has read entries". When false, not
all entries in the directory are in the file mgr, when true, they are.
- 2. Instead of stat'ing the file in FileManager::getFile, check to see if
+ 2. Instead of stat'ing the file in FileManager::getFile, check to see if
the dir has been read. If so, fail immediately, if not, read the dir,
then retry.
- 3. Reading the dir uses the getdirentries syscall, creating an FileEntry
+ 3. Reading the dir uses the getdirentries syscall, creating a FileEntry
for all files found.
-//===---------------------------------------------------------------------===//
-
-TODO: Fast #Import:
-
- * Get frameworks that don't use #import to do so, e.g.
- DirectoryService, AudioToolbox, CoreFoundation, etc. Why not using #import?
- Because they work in C mode? C has #import.
- * Have the lexer return a token for #import instead of handling it itself.
- - Create a new preprocessor object with no external state (no -D/U options
- from the command line, etc). Alternatively, keep track of exactly which
- external state is used by a #import: declare it somehow.
- * When having reading a #import file, keep track of whether we have (and/or
- which) seen any "configuration" macros. Various cases:
- - Uses of target args (__POWERPC__, __i386): Header has to be parsed
- multiple times, per-target. What about #ifndef checks? How do we know?
- - "Configuration" preprocessor macros not defined: POWERPC, etc. What about
- things like __STDC__ etc? What is and what isn't allowed.
- * Special handling for "umbrella" headers, which just contain #import stmts:
- - Cocoa.h/AppKit.h - Contain pointers to digests instead of entire digests
- themselves? Foundation.h isn't pure umbrella!
- * Frameworks digests:
- - Can put "digest" of a framework-worth of headers into the framework
- itself. To open AppKit, just mmap
- /System/Library/Frameworks/AppKit.framework/"digest", which provides a
- symbol table in a well defined format. Lazily unstream stuff that is
- needed. Contains declarations, macros, and debug information.
- - System frameworks ship with digests. How do we handle configuration
- information? How do we handle stuff like:
- #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_2
- which guards a bunch of decls? Should there be a couple of default
- configs, then have the UI fall back to building/caching its own?
- - GUI automatically builds digests when UI is idle, both of system
- frameworks if they aren't not available in the right config, and of app
- frameworks.
- - GUI builds dependence graph of frameworks/digests based on #imports. If a
- digest is out date, dependent digests are automatically invalidated.
-
- * New constraints on #import for objc-v3:
- - #imported file must not define non-inline function bodies.
- - Alternatively, they can, and these bodies get compiled/linked *once*
- per app into a dylib. What about building user dylibs?
- - Restrictions on ObjC grammar: can't #import the body of a for stmt or fn.
- - Compiler must detect and reject these cases.
- - #defines defined within a #import have two behaviors:
- - By default, they escape the header. These macros *cannot* be #undef'd
- by other code: this is enforced by the front-end.
- - Optionally, user can specify what macros escape (whitelist) or can use
- #undef.
-
-//===---------------------------------------------------------------------===//
-
-TODO: New language feature: Configuration queries:
- - Instead of #ifdef __POWERPC__, use "if (strcmp(`cpu`, __POWERPC__))", or
- some other, better, syntax.
- - Use it to increase the number of "architecture-clean" #import'd files,
- allowing a single index to be used for all fat slices.
-
//===---------------------------------------------------------------------===//
// Specifying targets: -triple and -arch
-===---------------------------------------------------------------------===//
+//===---------------------------------------------------------------------===//
-The clang supports "-triple" and "-arch" options. At most one -triple option may
-be specified, while multiple -arch options can be specified. Both are optional.
+The clang supports "-triple" and "-arch" options. At most one -triple and one
+-arch option may be specified. Both are optional.
The "selection of target" behavior is defined as follows:
-(1) If the user does not specify -triple:
-
- (a) If no -arch options are specified, the target triple used is the host
- triple (in llvm/Config/config.h).
-
- (b) If one or more -arch's are specified (and no -triple), then there is
- one triple for each -arch, where the specified arch is substituted
- for the arch in the host triple. Example:
-
- host triple = i686-apple-darwin9
- command: clang -arch ppc -arch ppc64 ...
- triples used: ppc-apple-darwin9 ppc64-apple-darwin9
-
-(2) The user does specify a -triple (only one allowed):
-
- (a) If no -arch options are specified, the triple specified by -triple
- is used. E.g clang -triple i686-apple-darwin9
-
- (b) If one or more -arch options are specified, then the triple specified
- by -triple is used as the primary target, and the arch's specified
- by -arch are used to create secondary targets. For example:
-
- clang -triple i686-apple-darwin9 -arch ppc -arch ppc64
-
- has the following targets:
-
- i686-apple-darwin9 (primary target)
- ppc-apple-darwin9 (secondary target)
- ppc64-apple-darwin9 (secondary target)
-
-The secondary targets are used in the 'portability' model (see below).
+(1) If the user does not specify -triple, we default to the host triple.
+(2) If the user specifies a -arch, that overrides the arch in the host or
+ specified triple.
//===---------------------------------------------------------------------===//
-The 'portability' model in clang is sufficient to catch translation units (or
-their parts) that are not portable, but it doesn't help if the system headers
-are non-portable and not fixed. An alternative model that would be easy to use
-is a 'tainting' scheme. Consider:
-
-int32_t
-OSHostByteOrder(void) {
-#if defined(__LITTLE_ENDIAN__)
- return OSLittleEndian;
-#elif defined(__BIG_ENDIAN__)
- return OSBigEndian;
-#else
- return OSUnknownByteOrder;
-#endif
-}
-It would be trivial to mark 'OSHostByteOrder' as being non-portable (tainted)
-instead of marking the entire translation unit. Then, if OSHostByteOrder is
-never called/used by the current translation unit, the t-u wouldn't be marked
-non-portable. However, there is no good way to handle stuff like:
+verifyInputConstraint and verifyOutputConstraint should not return bool.
-extern int X, Y;
+Instead we should return something like:
-#ifndef __POWERPC__
-#define X Y
-#endif
+enum VerifyConstraintResult {
+ Valid,
-int bar() { return X; }
+ // Output only
+ OutputOperandConstraintLacksEqualsCharacter,
+ MatchingConstraintNotValidInOutputOperand,
-When compiling for powerpc, the #define is skipped, so it doesn't know that bar
-uses a #define that is set on some other target. In practice, limited cases
-could be handled by scanning the skipped region of a #if, but the fully general
-case cannot be implemented efficiently. In this case, for example, the #define
-in the protected region could be turned into either a #define_target or
-#define_other_target as appropriate. The harder case is code like this (from
-OSByteOrder.h):
+ // Input only
+ InputOperandConstraintContainsEqualsCharacter,
+ MatchingConstraintReferencesInvalidOperandNumber,
- #if (defined(__ppc__) || defined(__ppc64__))
- #include <libkern/ppc/OSByteOrder.h>
- #elif (defined(__i386__) || defined(__x86_64__))
- #include <libkern/i386/OSByteOrder.h>
- #else
- #include <libkern/machine/OSByteOrder.h>
- #endif
+ // Both
+ PercentConstraintUsedWithLastOperand
+};
-The realistic way to fix this is by having an initial #ifdef __llvm__ that
-defines its contents in terms of the llvm bswap intrinsics. Other things should
-be handled on a case-by-case basis.
-
-
-We probably have to do something smarter like this in the future. The C++ header
-<limits> contains a lot of code like this:
+//===---------------------------------------------------------------------===//
- static const int digits10 = __LDBL_DIG__;
- static const int min_exponent = __LDBL_MIN_EXP__;
- static const int min_exponent10 = __LDBL_MIN_10_EXP__;
- static const float_denorm_style has_denorm
- = bool(__LDBL_DENORM_MIN__) ? denorm_present : denorm_absent;
+Blocks should not capture variables that are only used in dead code.
- ... since this isn't being used in an #ifdef, it should be easy enough to taint
-the decl for these ivars.
+The rule that we came up with is that blocks are required to capture
+variables if they're referenced in evaluated code, even if that code
+doesn't actually rely on the value of the captured variable.
+For example, this requires a capture:
+ (void) var;
+But this does not:
+ if (false) puts(var);
-/usr/include/sys/cdefs.h contains stuff like this:
+Summary of <rdar://problem/9851835>: if we implement this, we should
+warn about non-POD variables that are referenced but not captured, but
+only if the non-reachability is not due to macro or template
+metaprogramming.
-#if defined(__ppc__)
-# if defined(__LDBL_MANT_DIG__) && defined(__DBL_MANT_DIG__) && \
- __LDBL_MANT_DIG__ > __DBL_MANT_DIG__
-# if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__-0 < 1040
-# define __DARWIN_LDBL_COMPAT(x) __asm("_" __STRING(x) "$LDBLStub")
-# else
-# define __DARWIN_LDBL_COMPAT(x) __asm("_" __STRING(x) "$LDBL128")
-# endif
-# define __DARWIN_LDBL_COMPAT2(x) __asm("_" __STRING(x) "$LDBL128")
-# define __DARWIN_LONG_DOUBLE_IS_DOUBLE 0
-# else
-# define __DARWIN_LDBL_COMPAT(x) /* nothing */
-# define __DARWIN_LDBL_COMPAT2(x) /* nothing */
-# define __DARWIN_LONG_DOUBLE_IS_DOUBLE 1
-# endif
-#elif defined(__i386__) || defined(__ppc64__) || defined(__x86_64__)
-# define __DARWIN_LDBL_COMPAT(x) /* nothing */
-# define __DARWIN_LDBL_COMPAT2(x) /* nothing */
-# define __DARWIN_LONG_DOUBLE_IS_DOUBLE 0
-#else
-# error Unknown architecture
-#endif
+//===---------------------------------------------------------------------===//
-An ideal way to solve this issue is to mark __DARWIN_LDBL_COMPAT /
-__DARWIN_LDBL_COMPAT2 / __DARWIN_LONG_DOUBLE_IS_DOUBLE as being non-portable
-because they depend on non-portable macros. In practice though, this may end
-up being a serious problem: every use of printf will mark the translation unit
-non-portable if targetting ppc32 and something else.
+We can still apply a modified version of the constructor/destructor
+delegation optimization in cases of virtual inheritance where:
+ - there is no function-try-block,
+ - the constructor signature is not variadic, and
+ - the parameter variables can safely be copied and repassed
+ to the base constructor because either
+ - they have not had their addresses taken by the vbase initializers or
+ - they were passed indirectly.
//===---------------------------------------------------------------------===//
-
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