[LLVMbugs] [Bug 13012] New: Support -fpcc-struct-return (IsSmallStructInRegABI)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=13012

             Bug #: 13012
           Summary: Support -fpcc-struct-return (IsSmallStructInRegABI)
           Product: clang
           Version: trunk
          Platform: Macintosh
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Driver
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: arthur.j.odwyer at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


We're trying to compile some C code with clang on Darwin (Mac OS X), but for
very specific and obscure reasons we'd like the generated code to use the
-fpcc-struct-return convention to return small structs on the stack, instead of
in EAX/EDX.

GCC provides the options -fpcc-struct-return, -freg-struct-return to switch
between the two possible conventions. Clang doesn't implement these options
yet. It would make our lives a tiny bit easier if Clang did.

Back in 2009, David Chisnall proposed a refactoring of some related code to
change the default convention for FreeBSD, but this patch didn't go so far as
to suggest a command-line option.
http://lists.cs.uiuc.edu/pipermail/cfe-dev/2009-August/006125.html
http://lists.cs.uiuc.edu/pipermail/cfe-dev/2009-August/006161.html

The code to select the value of IsSmallStructInRegABI appears to be in
"lib/CodeGen/TargetInfo.cpp".

Ideally, you'd probably like to refactor the whole thing so that the booleans
IsDarwinVectorABI, IsSmallStructInRegABI, IsMMXDisabled, and
IsWin32FloatStructABI were all independently switchable via the command line,
rather than hard-coded "guessing" based on the target system's triple.

-- 
Configure bugmail: http://llvm.org/bugs/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.