[LLVMbugs] [Bug 20700] New: Integrated arm assembler doesn't accept -mfpu=neon as -Wa argument

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon Aug 18 11:38:14 PDT 2014


            Bug ID: 20700
           Summary: Integrated arm assembler doesn't accept -mfpu=neon as
                    -Wa argument
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Driver
          Assignee: unassignedclangbugs at nondot.org
          Reporter: nicolasweber at gmx.de
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Consider that you're trying to detect neon support at runtime, and use neon
code if the processor supports it.

One approach to go about this (used by libvpx, used in chromium) is to build
your c files without -mfpu=neon, and have neon assembly in .S files (and the c
files then call the .S files).

The .S files don't have ".fpu neon" instructions for various reasons (one of
them being that clang didn't support .fpu neon until 2 days ago). The build
system doesn't make it easy to only pass flags .S files.

So one approach would be to pass -Wa,-mfpu=neon. Then all c files are built
without neon instructions, but the neon code in the .S files assemble fine.

That works fine with gnu as, but the integrated assembler doesn't understand
-mfpu=neon as -Wa flag.

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