[llvm] r200422 - Turn on CU ranges if we've got multiple compile units in the same

[Eric Christopher]

On Wed, Jan 29, 2014 at 2:32 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>
>
> On Wed, Jan 29, 2014 at 2:26 PM, Eric Christopher <echristo at gmail.com>
> wrote:
>>
>> On Wed, Jan 29, 2014 at 2:23 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> >
>> >
>> >
>> > On Wed, Jan 29, 2014 at 2:06 PM, Eric Christopher <echristo at gmail.com>
>> > wrote:
>> >>
>> >> Author: echristo
>> >> Date: Wed Jan 29 16:06:27 2014
>> >> New Revision: 200422
>> >>
>> >> URL: http://llvm.org/viewvc/llvm-project?rev=200422&view=rev
>> >> Log:
>> >> Turn on CU ranges if we've got multiple compile units in the same
>> >> module since there's no range guarantee that we could make given
>> >> output order. This also fixes up the testcases that have multiple
>> >> CUs to have the correct range offset.
>> >
>> >
>> > What if LTO together a debug and non-debug module together? We'll still
>> > have
>> > one CU, but we'll have functions that aren't in that CU - and
>> > incorrectly
>> > describe that using an "all text" range?
>> >
>>
>> ... Short of saying "always use DW_AT_ranges" I don't have a good
>> solution for this. I'm somewhat down with that, but...
>
>
> Perhaps you were addressing this with the "there's no range guarantee that
> we could make given output order" (I'm not /quite/ sure how to parse that
> sentence) - but I thought we'd settled on the idea that we could rely on
> output order and just coalesce functions/ranges that came one after the
> other. Or did you come up with some cases that breaks down for/that we care
> about?
>

If you have functions that aren't associated with a particular CU
there's no way of knowing which functions those are. We can only rely
on the output order to determine whether or not a function is not
going to appear in debug info output. At least not at the moment. I
imagine if we were to do so we'd run into the assert at
DwarfDebug.cpp:1583 right now if we even tried linking the two modules
together. :\

> That way we'd still get high/low whenever it's contiguous, and otherwise
> we'd use ranges.
>

Still don't have this way of doing it in yet, but that's an idea yes.
I'll see how it works in practice.

-eric

>>
>>
>> -eric
>>
>> >>
>> >>
>> >> Modified:
>> >>     llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
>> >>     llvm/trunk/test/DebugInfo/X86/stmt-list-multiple-compile-units.ll
>> >>
>> >> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
>> >> URL:
>> >>
>> >> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp?rev=200422&r1=200421&r2=200422&view=diff
>> >>
>> >>
>> >> ==============================================================================
>> >> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp (original)
>> >> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp Wed Jan 29
>> >> 16:06:27
>> >> 2014
>> >> @@ -1119,10 +1119,12 @@ void DwarfDebug::endSections() {
>> >>    }
>> >>
>> >>    // For now only turn on CU ranges if we've explicitly asked for it,
>> >> -  // we have -ffunction-sections enabled, or we've emitted a function
>> >> -  // into a unique section. At this point all sections should be
>> >> finalized
>> >> -  // except for dwarf sections.
>> >> -  HasCURanges = DwarfCURanges || UsedNonDefaultText ||
>> >> +  // we have -ffunction-sections enabled, we've emitted a function
>> >> +  // into a unique section, or we're using LTO. If we're using LTO
>> >> then
>> >> +  // we can't know that any particular function in the module is
>> >> correlated
>> >> +  // to a particular CU and so we need to be conservative. At this
>> >> point
>> >> all
>> >> +  // sections should be finalized except for dwarf sections.
>> >> +  HasCURanges = DwarfCURanges || UsedNonDefaultText || (CUMap.size() >
>> >> 1)
>> >> ||
>> >>                  TargetMachine::getFunctionSections();
>> >>  }
>> >>
>> >>
>> >> Modified:
>> >> llvm/trunk/test/DebugInfo/X86/stmt-list-multiple-compile-units.ll
>> >> URL:
>> >>
>> >> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/DebugInfo/X86/stmt-list-multiple-compile-units.ll?rev=200422&r1=200421&r2=200422&view=diff
>> >>
>> >>
>> >> ==============================================================================
>> >> --- llvm/trunk/test/DebugInfo/X86/stmt-list-multiple-compile-units.ll
>> >> (original)
>> >> +++ llvm/trunk/test/DebugInfo/X86/stmt-list-multiple-compile-units.ll
>> >> Wed
>> >> Jan 29 16:06:27 2014
>> >> @@ -8,11 +8,11 @@
>> >>  ; CHECK: .debug_info contents:
>> >>  ; CHECK: DW_TAG_compile_unit
>> >>  ; CHECK: DW_AT_stmt_list [DW_FORM_sec_offset]   (0x00000000)
>> >> -; CHECK: DW_AT_low_pc [DW_FORM_addr]       (0x0000000000000000)
>> >> +; CHECK: DW_AT_ranges [DW_FORM_sec_offset]      (0x00000000)
>> >>
>> >>  ; CHECK: DW_TAG_compile_unit
>> >>  ; CHECK: DW_AT_stmt_list [DW_FORM_sec_offset]   (0x0000003c)
>> >> -; CHECK: DW_AT_low_pc [DW_FORM_addr]       (0x0000000000000000)
>> >> +; CHECK: DW_AT_ranges [DW_FORM_sec_offset]      (0x00000020)
>> >>
>> >>  ; CHECK: .debug_line contents:
>> >>  ; CHECK-NEXT: Line table prologue:
>> >> @@ -25,12 +25,12 @@
>> >>
>> >>  ; DWARF3: .debug_info contents:
>> >>  ; DWARF3: DW_TAG_compile_unit
>> >> -; DWARF3: DW_AT_stmt_list [DW_FORM_data4]   (0x00000000)
>> >> -; DWARF3: DW_AT_low_pc [DW_FORM_addr]       (0x0000000000000000)
>> >> +; DWARF3: DW_AT_stmt_list [DW_FORM_data4]    (0x00000000)
>> >> +; DWARF3: DW_AT_ranges [DW_FORM_data4]       (0x00000000)
>> >>
>> >>  ; DWARF3: DW_TAG_compile_unit
>> >>  ; DWARF3: DW_AT_stmt_list [DW_FORM_data4]   (0x0000003c)
>> >> -; DWARF3: DW_AT_low_pc [DW_FORM_addr]       (0x0000000000000000)
>> >> +; DWARF3: DW_AT_ranges [DW_FORM_data4]      (0x00000020)
>> >>
>> >>  ; DWARF3: .debug_line contents:
>> >>  ; DWARF3-NEXT: Line table prologue:
>> >>
>> >>
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>> >
>> >
>
>