[LLVMbugs] [Bug 8794] New: DwarfDebug emits DW_AT_frame_base even when no frame base exists

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=8794

           Summary: DwarfDebug emits DW_AT_frame_base even when no frame
                    base exists
           Product: new-bugs
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: richard.relph at amd.com
                CC: llvmbugs at cs.uiuc.edu


For some targets (e.g. GPUs), programs are usually sufficiently small that the
entire program (an OpenCL kernel) is inlined. Such programs do not have a frame
pointer or a stack pointer.

We would like DwarfDebug::updateSubprogramScopeDIE() to not emit
DW_AT_frame_base when there is no frame base.

I had thought that using hasFP() to conditionally emit DW_AT_frame_base would
fix the problem. But probably not. Our target always returns false from
hasFP(), but I understand that other targets do not return a static true or
false. Some use hasFP() to differentiate between when FP and SP is used as
'frame base'.

What I think is needed is a way for getFrameRegister() to return as
recognizable "no frame" value and have updateSubprogramScopeDIE() test for it
before emitting DW_AT_frame_base.

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