[LLVMbugs] [Bug 16294] New: implement __builtin_assume_aligned()

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16294

            Bug ID: 16294
           Summary: implement __builtin_assume_aligned()
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: conradsand.arma at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Hello,

Thanks for your work on clang.  It would be very useful to implement the
__builtin_assume_aligned() function, which allows the compiler to assume that
the returned pointer is aligned (to a user specified number of bytes). This can
help in automatic vectorisation, allowing the compiler to use aligned SSE2
instructions.

GCC 4.7+ has this:
http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html

The __builtin_assume_aligned() function is used to speed up software such as
the Armadillo C++ linear algebra library:
http://arma.sourceforge.net/

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