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__atomic_test_and_set, __atomic_clear, plus a pile of undocumented __GCC_* predefined macros. Implement library fallback for __atomic_is_lock_free and __c11_atomic_is_lock_free, and implement __atomic_always_lock_free. Contrary to their documentation, GCC's __atomic_fetch_add family don't multiply the operand by sizeof(T) when operating on a pointer type. libstdc++ relies on this quirk. Remove this handling for all but the __c11_atomic_fetch_add and __c11_atomic_fetch_sub builtins. Contrary to their documentation, __atomic_test_and_set and __atomic_clear take a first argument of type 'volatile void *', not 'void *' or 'bool *', and __atomic_is_lock_free and __atomic_always_lock_free have an argument of type 'const volatile void *', not 'void *'. With this change, libstdc++4.7's <atomic> passes libc++'s atomic test suite, except for a couple of libstdc++ bugs and some cases where libc++'s test suite tests for properties which implementations have latitude to vary. llvm-svn: 154640
IRgen optimization opportunities. //===---------------------------------------------------------------------===// The common pattern of -- short x; // or char, etc (x == 10) -- generates an zext/sext of x which can easily be avoided. //===---------------------------------------------------------------------===// Bitfields accesses can be shifted to simplify masking and sign extension. For example, if the bitfield width is 8 and it is appropriately aligned then is is a lot shorter to just load the char directly. //===---------------------------------------------------------------------===// It may be worth avoiding creation of alloca's for formal arguments for the common situation where the argument is never written to or has its address taken. The idea would be to begin generating code by using the argument directly and if its address is taken or it is stored to then generate the alloca and patch up the existing code. In theory, the same optimization could be a win for block local variables as long as the declaration dominates all statements in the block. NOTE: The main case we care about this for is for -O0 -g compile time performance, and in that scenario we will need to emit the alloca anyway currently to emit proper debug info. So this is blocked by being able to emit debug information which refers to an LLVM temporary, not an alloca. //===---------------------------------------------------------------------===// We should try and avoid generating basic blocks which only contain jumps. At -O0, this penalizes us all the way from IRgen (malloc & instruction overhead), all the way down through code generation and assembly time. On 176.gcc:expr.ll, it looks like over 12% of basic blocks are just direct branches! //===---------------------------------------------------------------------===//