Commit Graph

510 Commits

Author SHA1 Message Date
Chen Zheng 474057f4c1 [Debug-Info] change return type to void for attribute adding functions.
Make following function return void:

    addLabel()
    addSectionLabel()
    addSectionDelta()

This aligns with other attributes adding functions.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D101022
2021-04-23 04:16:55 -04:00
Sourabh Singh Tomar 8252baa8c1 [DebugInfo] Support for signed constants inside DIExpression
Negative numbers are represented using DW_OP_consts along with signed representation
of the number as the argument.

Test case IR is generated using Fortran front-end.

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D99273
2021-03-30 23:20:38 +05:30
Alok Kumar Sharma 298016b1b1 [DebugInfo] Upgrade DISubragne::count to accept DIExpression also
This is needed for Fortran assumed shape arrays whose dimensions are
defined as,
  - 'count' is taken from array descriptor passed as parameter by
    caller, access from descriptor is defined by type DIExpression.
  - 'lowerBound' is defined by callee.
The current alternate way represents using upperBound in place of
count, where upperBound is calculated in callee in a temp variable
using lowerBound and count

Representation with count (DIExpression) is not only clearer as
compared to upperBound (DIVariable) but it has another advantage that
variable count is accessed by being parameter has better chance of
survival at higher optimization level than upperBound being local
variable.

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D99335
2021-03-30 09:16:55 +05:30
Chen Zheng 28da0778f7 [debug-info] refactor emitDwarfUnitLength
remove `Hi` `Lo` argument from `emitDwarfUnitLength`, so we
can make caller of emitDwarfUnitLength easier.

Reviewed By: MaskRay, dblaikie, ikudrin

Differential Revision: https://reviews.llvm.org/D96409
2021-02-25 21:00:25 -05:00
Kazu Hirata 5e80e5c119 [CodeGen] Use range-based for loops (NFC) 2021-02-15 14:46:11 -08:00
Kazu Hirata 296ee17661 [AsmPrinter] Use range-based for loops (NFC) 2021-02-10 20:01:22 -08:00
Jeremy Morse 102262e880 Revert "Re-land D94976 after revert in e29552c5aff6"
Maskray has reported a fault with .debug_gnu_pubnames in the comments on
D94976, caused by this patch, reverting to investigate.

This reverts commit 8998f5843503773c2f51fd475e2c77c687a65ee6.
2021-02-08 12:41:12 +00:00
Jeremy Morse 3d6802a222 Revert "DebugInfo: Temporarily work around -gsplit-dwarf + LTO .debug_gnu_pubnames regression after D94976"
Backing out this workaround to focus on fixing whatever's wrong with
.debug_gnu_pubnames, I'll revert the cause, (8998f584) in the next commit.

This reverts commit 56fa34ae3570a34fd0f4c2cf1bfaf095da01a959.
2021-02-08 12:41:01 +00:00
Fangrui Song 5481fc6d44 DebugInfo: Temporarily work around -gsplit-dwarf + LTO .debug_gnu_pubnames regression after D94976
`-flto -gsplit-dwarf -g -O[123]` may create .debug_gnu_pubnames with 0 DIE
offset entries. llvm-dwarfdump -debug-gnu-pubnames/ld.lld --gdb-index errors for that.

```
        .section        .debug_gnu_pubnames,"",@progbits
        .long   .LpubNames_end2-.LpubNames_begin2 # Length of Public Names Info
.LpubNames_begin2:
        .short  2                               # DWARF Version
        .long   .Lcu_begin2                     # Offset of Compilation Unit Info
        .long   57                              # Compilation Unit Length
        .long   0                               # DIE offset
        .byte   16                              # Attributes: TYPE, EXTERNAL
        .asciz  "absl"                          # External Name
        .long   0                               # DIE offset
        .byte   16                              # Attributes: TYPE, EXTERNAL
        .asciz  "absl::base_internal"           # External Name
        .long   0                               # End Mark
```
2021-02-04 17:35:09 -08:00
Jeremy Morse 1dab9824e4 Re-land D94976 after revert in e29552c5aff6
This modified patch avoids redirecting the unit in which a subprogram is
created if type units are enabled -- DIEs were getting children allocated
from different units memory pools. Original commit message:

[DWARF] Create subprogram's DIE in DISubprogram's unit

This is a fix for PR48790. Over in D70350, subprogram DIEs were permitted
to be shared between CUs. However, the creation of a subprogram DIE can be
triggered early, from other CUs. The subprogram definition is then created
in one CU, and when the function is actually emitted children are attached
to the subprogram that expect to be in another CU. This breaks internal CU
references in the children.

Fix this by redirecting the creation of subprogram DIEs in
getOrCreateContextDIE to the CU specified by it's DISubprogram definition.
This ensures that the subprogram DIE is always created in the correct CU.

Differential Revision: https://reviews.llvm.org/D94976
2021-02-04 11:17:18 +00:00
David Blaikie 266d73d7f0 DebugInfo: Add a DWARF FORM extension for addrx+offset references to reduce relocations
This is an alternative to the use of complex DWARF expressions for
addresses - shaving off a few extra bytes of expression overhead.
2021-01-28 10:20:02 -08:00
Shaurya Gupta e387e1d835 Revert "[DWARF] Create subprogram's DIE in DISubprogram's unit"
This reverts commit ef0dcb506300dc9644e8000c6028d14214be9d97.

This change is causing a lot of compiler crashes inside, sorry I don't have a
small repro/stacktrace with symbols to share right now.

Differential Revision: https://reviews.llvm.org/D95622
2021-01-28 16:39:01 +00:00
David Blaikie 94830306c1 DebugInfo: Fix bug in addr+offset exprloc to use DWARFv5 addrx op instead of DWARFv4 GNU extension 2021-01-27 18:39:44 -08:00
David Blaikie 19cd3f5c02 DebugInfo: Deduplicate addresses in debug_addr
Experimental, using non-existent DWARF support to use an expr for the
location involving an addr_index (to compute address + offset so
addresses can be reused in more places).

The global variable debug info had to be deferred until the end of the
module (so bss variables would all be emitted first - so their labels
would have the relevant section). Non-bss variables seemed to not have
their label assigned to a section even at the end of the module, so I
didn't know what to do there.

Also, the hashing code is broken - doesn't know how to hash these
expressions (& isn't hashing anything inside subprograms, which seems
problematic), so for test purposes this change just skips the hash
computation. (GCC's actually overly sensitive in its hash function, it
seems - I'm forgetting the specific case right now - anyway, we might
want to just use the frontend-known file hash and give up on optimistic
.dwo/.dwp reuse)
2021-01-27 14:00:43 -08:00
Jeremy Morse 1f513e79c9 [DWARF] Create subprogram's DIE in DISubprogram's unit
This is a fix for PR48790. Over in D70350, subprogram DIEs were permitted
to be shared between CUs. However, the creation of a subprogram DIE can be
triggered early, from other CUs. The subprogram definition is then created
in one CU, and when the function is actually emitted children are attached
to the subprogram that expect to be in another CU. This breaks internal CU
references in the children.

Fix this by redirecting the creation of subprogram DIEs in
getOrCreateContextDIE to the CU specified by it's DISubprogram definition.
This ensures that the subprogram DIE is always created in the correct CU.

Differential Revision: https://reviews.llvm.org/D94976
2021-01-27 12:36:14 +00:00
Chih-Ping Chen c44b393235 [DebugInfo] Support Fortran 'use <external module>' statement.
The main change is to add a 'IsDecl' field to DIModule so
that when IsDecl is set to true, the debug info entry generated
for the module would be marked as a declaration. That way, the debugger
would look up the definition of the module in the gloabl scope.

Please see the comments in llvm/test/DebugInfo/X86/dimodule.ll
for what the debug info entries would look like.

Differential Revision: https://reviews.llvm.org/D93462
2020-12-18 13:10:57 -05:00
Chih-Ping Chen 9456b8d168 [DebugInfo] Add handling of stringLengthExp operand of DIStringType.
This patch makes DWARF writer emit DW_AT_string_length using
the stringLengthExp operand of DIStringType.

This is part of the effort to add debug info support for
Fortran deferred length strings.

Also updated the tests to exercise the change.

Differential Revision: https://reviews.llvm.org/D92412
2020-12-08 14:49:59 -05:00
Fangrui Song 840325e8ac AsmPrinter/Dwarf*: Use llvm::Register instead of unsigned 2020-11-06 21:00:28 -08:00
Fangrui Song 878101132b [DebugInfo] Delete unused DwarfUnit::addConstantFPValue & addConstantValue overloads. NFC
This functions appear to be unused for many years.
2020-11-04 00:05:57 -08:00
Amy Huang 2d226e1751 Recommit "[CodeView] Emit static data members as S_CONSTANTs."
We used to only emit static const data members in CodeView as
S_CONSTANTS when they were used; this patch makes it so they are always emitted.

This changes CodeViewDebug.cpp to find the static const members from the
class debug info instead of creating DIGlobalVariables in the IR
whenever a static const data member is used.

Bug: https://bugs.llvm.org/show_bug.cgi?id=47580

Differential Revision: https://reviews.llvm.org/D89072

This reverts commit 504615353f31136dd6bf7a971b6c236fd70582be.
2020-10-28 16:35:59 -07:00
Alok Kumar Sharma 0d9afcbbba [DebugInfo] Support for DW_TAG_generic_subrange
This is needed to support fortran assumed rank arrays which
have runtime rank.

  Summary:
Fortran assumed rank arrays have dynamic rank. DWARF TAG
DW_TAG_generic_subrange is needed to support that.

  Testing:
unit test cases added (hand-written)
check llvm
check debug-info

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D89218
2020-10-29 01:34:15 +05:30
Alok Kumar Sharma 0a8029e199 [DebugInfo] Support for DWARF attribute DW_AT_rank
This patch adds support for DWARF attribute DW_AT_rank.

  Summary:
Fortran assumed rank arrays have dynamic rank. DWARF attribute
DW_AT_rank is needed to support that.

  Testing:
unit test cases added (hand-written)
check llvm
check debug-info

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D89141
2020-10-10 17:51:12 +05:30
Simon Pilgrim b6c38b504d DwarfUnit.h - remove unnecessary includes. NFCI. 2020-09-16 18:32:29 +01:00
Igor Kudrin c78a1901e4 [DebugInfo] Fix emitting DWARF64 type units (10/19).
The patch fixes emitting the offset to the type DIE. All other fields
are already fixed in previous patches.

Differential Revision: https://reviews.llvm.org/D87021
2020-09-15 11:31:07 +07:00
Igor Kudrin 18e824ea67 [DebugInfo] Fix emitting DWARF64 DWO compilation units and string offset tables (9/19).
These two fixes are better to go together because llvm-dwarfdump is
unable to dump a table when another one is malformed.

Differential Revision: https://reviews.llvm.org/D87018
2020-09-15 11:31:00 +07:00
Igor Kudrin 4a475ed16e [DebugInfo] Use a common method to determine a suitable form for section offsts (6/19).
This is mostly an NFC patch because the involved methods are used when
emitting DWO files, which is incompatible with DWARFv3, or for platforms
where DWARF64 is not supported yet.

Differential Revision: https://reviews.llvm.org/D87015
2020-09-15 11:30:38 +07:00
Igor Kudrin a68bb0aa01 [DebugInfo] Fix emitting DWARF64 compilation units (5/19).
The patch also adds a method to choose an appropriate DWARF form
to represent section offsets according to the version and the format
of producing debug info.

Differential Revision: https://reviews.llvm.org/D87014
2020-09-15 11:30:30 +07:00
Amy Huang 63a262cd97 [DebugInfo] Make DWARF ignore sizes on forward declared class types.
Make sure the sizes for forward declared classes aren't emitted in
DWARF.

This comes before https://reviews.llvm.org/D87062, which adds sizes to
all classes with definitions.

Bug: https://bugs.llvm.org/show_bug.cgi?id=47338

Differential Revision: https://reviews.llvm.org/D87070
2020-09-03 11:01:49 -07:00
Sander de Smalen 33c91e76d2 [AArch64][SVE] Add missing debug info for ACLE types.
This patch adds type information for SVE ACLE vector types,
by describing them as vectors, with a lower bound of 0, and
an upper bound described by a DWARF expression using the
AArch64 Vector Granule register (VG), which contains the
runtime multiple of 64bit granules in an SVE vector.

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D86101
2020-08-27 10:56:42 +01:00
Sourabh Singh Tomar 9241b8151b [DebugInfo][flang]Added support for representing Fortran assumed length strings
This patch adds support for representing Fortran `character(n)`.

Primarily patch is based out of D54114 with appropriate modifications.

Test case IR is generated using our downstream classic-flang. We're in process
of upstreaming flang PR's but classic-flang has dependencies on llvm, so
this has to get in first.

Patch includes functional test case for both IR and corresponding
dwarf, furthermore it has been manually tested as well using GDB.

Source snippet:
```
 program assumedLength
   call sub('Hello')
   call sub('Goodbye')
   contains
   subroutine sub(string)
           implicit none
           character(len=*), intent(in) :: string
           print *, string
   end subroutine sub
 end program assumedLength
```

GDB:
```
(gdb) ptype string
type = character (5)
(gdb) p string
$1 = 'Hello'
```

Reviewed By: aprantl, schweitz

Differential Revision: https://reviews.llvm.org/D86305
2020-08-22 10:13:40 +05:30
David Blaikie cafedbe4d6 DebugInfo: Emit class template parameters first, before members
This reads more like what you'd expect the DWARF to look like (from the
lexical order of C++ - template parameters come before members, etc),
and also happens to make it easier to tickle (& thus test) a bug related
to type units and Split DWARF I'm about to fix.
2020-08-17 21:42:00 -07:00
Igor Kudrin eabe546cbc [DebugInfo] Clean up DIEUnit. NFC.
This removes members of the DIEUnit class which were used only in unit
tests. Note also that child classes shadowed some of these methods,
namely, getDwarfVersion() was overridden in DwartfUnit and getLength()
was overridden in DwarfCompileUnit.

Differential Revision: https://reviews.llvm.org/D85436
2020-08-07 15:55:44 +07:00
Igor Kudrin 46e237eb24 [DebugInfo] Fix misleading using of DWARF forms with DIELabel. NFCI.
DIELabel can emit only 32- or 64-bit values, while it was created in
some places with DW_FORM_udata, which implies emitting uleb128.
Nevertheless, these places also expected to emit U32 or U64, but just
used a misleading DWARF form. The patch updates those places to use more
appropriate DWARF forms and restricts DIELabel::SizeOf() to accept only
forms that are actually used in the LLVM codebase.

Differential Revision: https://reviews.llvm.org/D84094
2020-08-03 15:04:08 +07:00
David Blaikie dc9888b6b6 DebugInfo: Move getMD5AsBytes from DwarfUnit to DwarfDebug
It wasn't using any state from DwarfUnit anyway.
2020-07-20 19:21:39 -07:00
Alok Kumar Sharma 0a592fd282 [DebugInfo] Support for DW_AT_associated and DW_AT_allocated.
Summary:
This support is needed for the Fortran array variables with pointer/allocatable
attribute. This support enables debugger to identify the status of variable
whether that is currently allocated/associated.

  for pointer array (before allocation/association)
  without DW_AT_associated

(gdb) pt ptr
type = integer (140737345375288:140737354129776)
(gdb) p ptr
value requires 35017956 bytes, which is more than max-value-size

  with DW_AT_associated

(gdb) pt ptr
type = integer (:)
(gdb) p ptr
$1 = <not associated>

  for allocatable array (before allocation)

  without DW_AT_allocated

(gdb) pt arr
type = integer (140737345375288:140737354129776)
(gdb) p arr
value requires 35017956 bytes, which is more than max-value-size

  with DW_AT_allocated

(gdb) pt arr
type = integer, allocatable (:)
(gdb) p arr
$1 = <not allocated>

    Testing
- unit test cases added
- check-llvm
- check-debuginfo

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D83544
2020-07-20 19:54:35 +05:30
Alok Kumar Sharma 6077c65472 [DebugInfo] Upgrade DISubrange to support Fortran dynamic arrays
This patch upgrades DISubrange to support fortran requirements.

Summary:
Below are the updates/addition of fields.
lowerBound - Now accepts signed integer or DIVariable or DIExpression,
earlier it accepted only signed integer.
upperBound - This field is now added and accepts signed interger or
DIVariable or DIExpression.
stride - This field is now added and accepts signed interger or
DIVariable or DIExpression.
This is required to describe bounds of array which are known at runtime.

Testing:
unit test cases added (hand-written)
check clang
check llvm
check debug-info

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D80197
2020-05-28 13:46:41 +05:30
Alok Kumar Sharma 1daff0ecf4 [DebugInfo] support for DW_AT_data_location in llvm
This patch adds support for DWARF attribute DW_AT_data_location.

Summary:
Dynamic arrays in fortran are described by array descriptor and
data allocation address. Former is mapped to DW_AT_location and
later is mapped to DW_AT_data_location.

Testing:
unit test cases added (hand-written)
check llvm
check debug-info

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D79592
2020-05-15 11:33:17 +05:30
Sourabh Singh Tomar 99bc9bdea6 [DebugInfo] Fortran module DebugInfo support in LLVM
This patch extends DIModule Debug metadata in LLVM to support
Fortran modules. DIModule is extended to contain File and Line
fields, these fields will be used by Flang FE to create debug
information necessary for representing Fortran modules at IR level.

Furthermore DW_TAG_module is also extended to contain these fields.
If these fields are missing, debuggers like GDB won't be able to
show Fortran modules information correctly.

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D79484
2020-05-13 12:52:30 +05:30
LemonBoy 5ef1cd8cb9 [DebugInfo] Change DIEnumerator payload type from int64_t to APInt
This allows the representation of arbitrarily large enumeration values.
See https://lists.llvm.org/pipermail/llvm-dev/2017-December/119475.html for context.

Reviewed By: andrewrk, aprantl, MaskRay

Differential Revision: https://reviews.llvm.org/D62475
2020-04-18 12:49:31 -07:00
Adrian Prantl cacf43a80a Add debug info support for Swift/Clang APINotes.
In order for dsymutil to collect .apinotes files (which capture
attributes such as nullability, Swift import names, and availability),
I want to propose adding an apinotes: field to DIModule that gets
translated into a DW_AT_LLVM_apinotes (path) nested inside
DW_TAG_module. This will be primarily used by LLDB to indirectly
extract the Swift names of Clang declarations that were deserialized
from DWARF.

<rdar://problem/59514626>

Differential Revision: https://reviews.llvm.org/D75585
2020-03-11 18:47:30 -07:00
Awanish Pandey a442647ff8 [DebugInfo][DWARF5]: Added support for debuginfo generation for defaulted parameters
This patch adds support for dwarf emission/dumping part of debuginfo
generation for defaulted parameters.

Reviewers: probinson, aprantl, dblaikie

Reviewed By: aprantl, dblaikie

Differential Revision: https://reviews.llvm.org/D73462
2020-03-03 13:09:53 +05:30
Fangrui Song 13339a0dea [MCStreamer] De-capitalize EmitValue EmitIntValue{,InHex} 2020-02-14 23:08:40 -08:00
Fangrui Song e6d3f76ab0 [MC] De-capitalize another set of MCStreamer::Emit* functions
Emit{ValueTo,Code}Alignment Emit{DTP,TP,GP}* EmitSymbolValue etc
2020-02-14 19:26:52 -08:00
Fangrui Song 216ba73a16 [AsmPrinter] De-capitalize some AsmPrinter::Emit* functions
Similar to rL328848.
2020-02-13 13:38:33 -08:00
Vedant Kumar 3ce517d29d Reland (again): [DWARF] Allow cross-CU references of subprogram definitions
This is a revert-of-revert (i.e. this reverts commit 802bec89, which
itself reverted fa4701e1 and 79daafc9) with a fix folded in. The problem
was that call site tags weren't emitted properly when LTO was enabled
along with split-dwarf. This required a minor fix. I've added a reduced
test case in test/DebugInfo/X86/fission-call-site.ll.

Original commit message:

This allows a call site tag in CU A to reference a callee DIE in CU B
without resorting to creating an incomplete duplicate DIE for the callee
inside of CU A.

We already allow cross-CU references of subprogram declarations, so it
doesn't seem like definitions ought to be special.

This improves entry value evaluation and tail call frame synthesis in
the LTO setting. During LTO, it's common for cross-module inlining to
produce a call in some CU A where the callee resides in a different CU,
and there is no declaration subprogram for the callee anywhere. In this
case llvm would (unnecessarily, I think) emit an empty DW_TAG_subprogram
in order to fill in the call site tag. That empty 'definition' defeats
entry value evaluation etc., because the debugger can't figure out what
it means.

As a follow-up, maybe we could add a DWARF verifier check that a
DW_TAG_subprogram at least has a DW_AT_name attribute.

Update #1:

Reland with a fix to create a declaration DIE when the declaration is
missing from the CU's retainedTypes list. The declaration is left out
of the retainedTypes list in two cases:

1) Re-compiling pre-r266445 bitcode (in which declarations weren't added
   to the retainedTypes list), and
2) Doing LTO function importing (which doesn't update the retainedTypes
   list).

It's possible to handle (1) and (2) by modifying the retainedTypes list
(in AutoUpgrade, or in the LTO importing logic resp.), but I don't see
an advantage to doing it this way, as it would cause more DWARF to be
emitted compared to creating the declaration DIEs lazily.

Update #2:

Fold in a fix for call site tag emission in the split-dwarf + LTO case.

Tested with a stage2 ThinLTO+RelWithDebInfo build of clang, and with a
ReleaseLTO-g build of the test suite.

rdar://46577651, rdar://57855316, rdar://57840415, rdar://58888440

Differential Revision: https://reviews.llvm.org/D70350
2020-01-27 10:52:34 -08:00
Vedant Kumar 0e3d6e2d5b Revert "Reland: [DWARF] Allow cross-CU references of subprogram definitions"
... as well as:
Revert "[DWARF] Defer creating declaration DIEs until we prepare call site info"

This reverts commit fa4701e1979553c2df61698ac1ac212627630442.

This reverts commit 79daafc90308787b52a5d3a7586e82acd5e374b3.

There have been reports of this assert getting hit:

CalleeDIE && "Could not find DIE for call site entry origin
2020-01-24 18:07:54 -08:00
Awanish Pandey 437cb9c178 Recommit "[DWARF5][DebugInfo]: Added support for DebugInfo generation for auto return type for C++ member functions."
Summary:
This was reverted in 328e0f3dcac52171b8cdedeaba22c98e7fbb75ea due to
chromium bot failure. This revision addresses that case.

Original commit message:
Summary:
    This patch will provide support for auto return type for the C++ member
    functions. Before this return type of the member function is deduced and
    stored in the DIE.
    This patch includes llvm side implementation of this feature.

    Patch by: Awanish Pandey <Awanish.Pandey@amd.com>

    Reviewers: dblaikie, aprantl, shafik, alok, SouraVX, jini.susan.george

    Reviewed by: dblaikie

    Differential Revision: https://reviews.llvm.org/D70524
2020-01-20 15:13:13 +05:30
Adrian Prantl 3363ed7b0a Move the sysroot attribute from DIModule to DICompileUnit
[this re-applies c0176916a4824812d25a5a22c4ff7c95857b0cd6
 with the correct commit message and phabricator link]

This addresses point 1 of PR44213.
https://bugs.llvm.org/show_bug.cgi?id=44213

The DW_AT_LLVM_sysroot attribute is used for Clang module debug info,
to allow LLDB to import a Clang module from source. Currently it is
part of each DW_TAG_module, however, it is the same for all modules in
a compile unit. It is more efficient and less ambiguous to store it
once in the DW_TAG_compile_unit.

This should have no effect on DWARF consumers other than LLDB.

Differential Revision: https://reviews.llvm.org/D71732
2020-01-17 12:55:40 -08:00
Adrian Prantl e3aa322358 Revert "Rename DW_AT_LLVM_isysroot to DW_AT_LLVM_sysroot"
This reverts commit 12e479475a896f664fb721f98c2d6805185ac352.

I accidentally landed this patch with the wrong commit message ...
2020-01-17 12:52:36 -08:00
Adrian Prantl e436ebc793 Rename DW_AT_LLVM_isysroot to DW_AT_LLVM_sysroot
This is a purely cosmetic change that is NFC in terms of the binary
output. I bugs me that I called the attribute DW_AT_LLVM_isysroot
since the "i" is an artifact of GCC command line option syntax
(-isysroot is in the category of -i options) and doesn't carry any
useful information otherwise.

This attribute only appears in Clang module debug info.

Differential Revision: https://reviews.llvm.org/D71722
2020-01-17 09:36:48 -08:00