Hans Wennborg eeb828f029 Use returns_nonnull in BumpPtrAllocator and MallocAllocator to avoid null-check in placement new ... In both Clang and LLVM, this is a common pattern: Size = sizeof(DeclRefExpr) + SomeExtraStuff; void *Mem = Context.Allocate(Size, llvm::alignOf<DeclRefExpr>()); return new (Mem) DeclRefExpr(...); The annoying thing is that because the default placement-new operator has a nothrow specification, the compiler will insert a null check of Mem before calling the DeclRefExpr constructor. This null check is redundant for us, because we expect the allocation functions to never return null. By annotating the allocator functions with returns_nonnull, we can optimize away these checks. Compiling clang with a recent version of Clang and measuring with: $ perf stat -r20 bin/clang.patch -fsyntax-only -w gcc.c && perf stat -r20 bin/clang.orig -fsyntax-only -w gcc.c Shows a 2.4% speed-up (+- 0.8%). The pattern occurs in LLVM too. Measuring with -O3 (and now using bzip2.c instead, because it's smaller): $ perf stat -r20 bin/clang.patch -O3 -w bzip2.c && perf stat -r20 bin/clang.orig -O3 -w bzip2.c Shows 4.4 % speed-up (+- 1%). If anyone knows of a similar attribute we can use for MSVC, or some other technique to get rid off the null check there, please let me know. Differential Revision: http://reviews.llvm.org/D4989 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216192 91177308-0d34-0410-b5e6-96231b3b80d8		2014-08-21 17:10:00 +00:00
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llvm	Use returns_nonnull in BumpPtrAllocator and MallocAllocator to avoid null-check in placement new	2014-08-21 17:10:00 +00:00
llvm-c	Canonicalize header guards into a common format.	2014-08-13 16:26:38 +00:00