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Summary: This patch attempts to redo what was tried in r278783, but was reverted. These intrinsics should be available on non-windows platforms with "xsave" feature check. But on Windows platforms they shouldn't have feature check since that's how MSVC behaves. To accomplish this I've added a MS builtin with no feature check. And a normal gcc builtin with a feature check. When _MSC_VER is not defined _xgetbv/_xsetbv will be macros pointing to the gcc builtin name. I've moved the forward declarations from intrin.h to immintrin.h to match the MSDN documentation and used that as the header file for the MS builtin. I'm not super happy with this implementation, and I'm open to suggestions for better ways to do it. Reviewers: rnk, RKSimon, spatel Reviewed By: rnk Subscribers: cfe-commits Differential Revision: https://reviews.llvm.org/D56686 llvm-svn: 351160
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! //===---------------------------------------------------------------------===//