Take a StringRef instead of a "const char *".
Take a "std::error_code &" instead of a "std::string &" for error.
A create static method would be even better, but this patch is already a bit too
big.
llvm-svn: 216393
It makes no sense and can hide bugs. In particular, it lead
to left shift by 64 bits, which is an undefined behavior,
properly reported by UBSan.
llvm-svn: 216134
ARM in particular is getting dangerously close to exceeding 32 bits worth of
possible subtarget features. When this happens, various parts of MC start to
fail inexplicably as masks get truncated to "unsigned".
Mostly just refactoring at present, and there's probably no way to test.
llvm-svn: 215887
As X86MCAsmInfoDarwin uses '##' as CommentString although a single '#' starts a
comment a workaround for this special case is added.
Fixes divisions in constant expressions for the AArch64 assembler and other
targets which use '//' as CommentString.
Patch by Janne Grunau!
llvm-svn: 215615
Add header guards to files that were missing guards. Remove #endif comments
as they don't seem common in LLVM (we can easily add them back if we decide
they're useful)
Changes made by clang-tidy with minor tweaks.
llvm-svn: 215558
This removes the duplicate definition of GetXDataSection. This function is
available as a static method and is identical to the previous implementation.
This just cleans up the unnecessary duplication.
llvm-svn: 215289
This changes Win64EHEmitter into a utility WinEH UnwindEmitter that can be
shared across multiple architectures and a target specific bit which is
overridden (Win64::UnwindEmitter). This enables sharing the section selection
code across X86 and the intended use in ARM for emitting unwind information for
Windows on ARM.
llvm-svn: 215050
Duplicate the vararg tests for linux and add a tests which mixed
vararg arguments with darwin positional parameters.
Patch by: Janne Grunau <j@jannau.net>
llvm-svn: 214799
This makes EmitWindowsUnwindTables a virtual function and lowers the
implementation of the function to the X86WinCOFFStreamer. This method is a
target specific operation. This enables making the behaviour target dependent
by isolating it entirely to the target specific streamer.
llvm-svn: 214664
The frame information stored in this structure is driven by the requirements for
Windows NT unwinding rather than Windows 64 specifically. As a result, this
type can be shared across multiple architectures (ARM, AXP, MIPS, PPC, SH).
Rename this class in preparation for adding support for supporting unwinding
information for Windows on ARM.
Take the opportunity to constify the members as everything except the
ChainedParent is read-only. This required some adjustment to the label
handling.
llvm-svn: 214663
This patch adds code to emits the StackMap section on ELF systems. This section is required to support llvm.experimental.stackmap and llvm.experimental.patchpoint intrinsics.
Reviewers: ributzka, echristo
Differential Revision: http://reviews.llvm.org/D4574
llvm-svn: 214538
This recommits r208930, r208933, and r208975 (by reverting r209338) and
reverts r209529 (the FIXME to readd this functionality once the tools
were fixed) now that DWP has been fixed to cope with a single section
for all fission type units.
Original commit message:
"Since type units in the dwo file are handled by a debug aware tool,
they don't need to leverage the ELF comdat grouping to implement
deduplication. Avoid creating all the .group sections for these as a
space optimization."
llvm-svn: 213956
There were still some disassembler bits in lib/MC, but their use of Object
was only visible in the includes they used, not in the symbols.
llvm-svn: 213808
Having both Triple::arm64 and Triple::aarch64 is extremely confusing, and
invites bugs where only one is checked. In reality, the only legitimate
difference between the two (arm64 usually means iOS) is also present in the OS
part of the triple and that's what should be checked.
We still parse the "arm64" triple, just canonicalise it to Triple::aarch64, so
there aren't any LLVM-side test changes.
llvm-svn: 213743
As discussed in a previous checking to support the .localentry
directive on PowerPC, we need to inspect the actual target symbol
in needsRelocateWithSymbol to make the appropriate decision based
on that symbol's st_other bits.
Currently, needsRelocateWithSymbol does not get the target symbol.
However, it is directly available to its sole caller. This patch
therefore simply extends the needsRelocateWithSymbol by a new
parameter "const MCSymbolData &SD", passes in the target symbol,
and updates all derived implementations.
In particular, in the PowerPC implementation, this patch removes
the FIXME added by the previous checkin.
llvm-svn: 213487
This adds an optional parameter to the EmitSymbolValue method in MCStreamer to
permit emitting a symbol value as a section relative value. This is to cover
the use in MCDwarf which should not really know about how to emit a section
relative value for a given target.
This addresses post-review comments from Eric Christopher in SVN r213275.
llvm-svn: 213463
On AArch64 the pseudo instruction ldr <reg>, =... supports both
32-bit and 64-bit constants. Add support for 64 bit constants for
the pools to support the pseudo instruction fully.
Changes the AArch64 ldr-pseudo tests to use 32-bit registers and
adds tests with 64-bit registers.
Patch by Janne Grunau!
Differential Revision: http://reviews.llvm.org/D4279
llvm-svn: 213387
The header contains an offset to the DWARF abbreviations for the CU. The offset
must be section relative for COFF and absolute for others. The non-assembly
code path for the DWARF header generation already had the correct emission for
the headers. This corrects just the assembly path. Due to the invalid
relocation, processing of the debug information would halt previously on the
first assembly input as the associated abbreviations would be out of range as
they would have the location increased by image base and the section offset.
This address PR20332.
llvm-svn: 213275
Rather than use three EmitBytes, concatenate the string at compile time,
constructing a single StringRef and emitting the data in one shot. This also
creates nicer assembly output. NFC.
llvm-svn: 213273
This makes the opcode an opaque value (unsigned int) rather than the
enumeration. This permits the use of target specific operands.
Split out the generic type into a MCWinEH header and add a supporting
MCWin64EH::Instruction to abstract out the selection of the opcode and
construction of the actual instruction.
llvm-svn: 213221
COFF lacks a feature that other object file formats support: mergeable
sections.
To work around this, MSVC sticks constant pool entries in special COMDAT
sections so that each constant is in it's own section. This permits
unused constants to be dropped and it also allows duplicate constants in
different translation units to get merged together.
This fixes PR20262.
Differential Revision: http://reviews.llvm.org/D4482
llvm-svn: 213006
This is the first of a number of changes designed to generalise
MCWin64EHInstruction to support different target architectures. An ordered set
(vector) of these instructions is saved per frame to permit the emission of
information for Windows NT style unwinding. The only bit of information which
is actually target specific here is the Opcode for the unwinding bytecode. The
remainder of the information is simply generic information that is relevant to
the Windows NT unwinding model.
Remove the accessors for the fields, making them const and public instead. Sink
the knowledge of the alias'ed name into the single source and sink a single-use
check method into the use.
llvm-svn: 212914
Rename member variables and functions for the MCStreamer for DWARF-like
unwinding management. Rename the Windows ones as well and make the naming and
handling similar across the two. No functional change intended.
llvm-svn: 212912
MC was aping a binutils bug where aliases would default their linkage to
private instead of internal.
I've sent a patch to the binutils maintainers and they've recently
applied it to the GNU assembler sources.
This fixes PR20152.
Differential Revision: http://reviews.llvm.org/D4395
llvm-svn: 212899
Due to the fact that the windows unwinding has the concept of chained frames, we
maintain a current frame info pointer that is adjusted on any push and pop of a
unwinding context. This just removes an unnecessary variable that was used to
mirror the DWARF unwinding code.
llvm-svn: 212882
This structure contains information related to the call frame used to generate
unwinding information. Rename this to reflect the future use to represent the
shared state between various architectures for WinCFI information.
llvm-svn: 212881
This adds a utility method to access the WinCFI information in bulk and uses
that to iterate rather than requesting the count and individually iterating
them. This is in preparation for restructuring WinCFI handling to enable more
clear sharing across architectures to enable unwind information emission for
Windows on ARM.
llvm-svn: 212683
Use 0 for the invalid buffer instead of -1/~0 and switch to unsigned
representation to enable more idiomatic usage.
Also introduce a trivial SourceMgr::getMainFileID() instead of hard-coding 0/1
to identify the main file.
llvm-svn: 212398
Now that we have a lib/MC/MCAnalysis, the dependency was there just because
of two helper classes. Move the two over to MC.
This will allow IRObjectFile to parse inline assembly.
llvm-svn: 212248
The new library is 150KB on a Release+Asserts build, so it is quiet a bit of
code that regular users of MC don't need to link with now.
llvm-svn: 212209
This is a small targeted fix for pr20119. The code needs quiet a bit of
refactoring and I added some FIXMEs about it, but I want to get the testcase
passing first.
llvm-svn: 212101
seh_stackalloc 0 is not representable in Win64 SEH info, so emitting it
is a bug.
Reviewers: rnk
Differential Revision: http://reviews.llvm.org/D4334
Patch by Vadim Chugunov!
llvm-svn: 212081
Rename the routines to reflect the reality that they are more related to call
frame information than to Win64 EH. Although EH is implemented in an intertwined
manner by augmenting with an exception handler and an associated parameter, the
majority of these routines emit information required to unwind the frames. This
also helps identify that these routines are generic for most windows platforms
(they apply equally to nearly all architectures except x86) although the
encoding of the information is architecture dependent.
Unwinding data is emitted via EmitWinCFI* and exception handling information via
EmitWinEH*.
llvm-svn: 211994
COFF sections in MC were represented by a tuple of section-name and
COMDAT-name. This is not sufficient to represent a .text section
associated with another .text section; we need a way to distinguish
between the key section and the one marked associative.
llvm-svn: 211913
string_ostream is a safe and efficient string builder that combines opaque
stack storage with a built-in ostream interface.
small_string_ostream<bytes> additionally permits an explicit stack storage size
other than the default 128 bytes to be provided. Beyond that, storage is
transferred to the heap.
This convenient class can be used in most places an
std::string+raw_string_ostream pair or SmallString<>+raw_svector_ostream pair
would previously have been used, in order to guarantee consistent access
without byte truncation.
The patch also converts much of LLVM to use the new facility. These changes
include several probable bug fixes for truncated output, a programming error
that's no longer possible with the new interface.
llvm-svn: 211749
--
This patch enables LLVM to emit Win64-native unwind info rather than
DWARF CFI. It handles all corner cases (I hope), including stack
realignment.
Because the unwind info is not flexible enough to describe stack frames
with a gap of unknown size in the middle, such as the one caused by
stack realignment, I modified register spilling code to place all spills
into the fixed frame slots, so that they can be accessed relative to the
frame pointer.
Patch by Vadim Chugunov!
Reviewed By: rnk
Differential Revision: http://reviews.llvm.org/D4081
llvm-svn: 211691
In assembly the expression a=b is parsed as an assignment, so it should be
printed as one.
This remove a truly horrible hack for producing a label with "a=.". It would
be used by codegen but would never be reached by the asm parser. Sorry I
missed this when it was first committed.
llvm-svn: 211639
According Nick Kledzik (http://llvm.org/bugs/show_bug.cgi?id=19430#c2):
"... mach-o no longer needs names in the __eh_frame section (and has not for
years)."
Iain Sandoe confirms it is also unnecessary for their old darwin support.
llvm-svn: 211500
Utilize range based for-loops to simplify some code.
Use insert() instead of a loop for simplicity/efficiency.
No functionality change.
llvm-svn: 211486
Correct the section flags for code built for Windows on ARM with
`-ffunction-sections`. Windows on ARM uses solely Thumb-2 instructions, and
indicates that the function is thumb by placing it in a text section that has
IMAGE_SCN_MEM_16BIT flag set.
When we encounter a .section directive, a new section is constructed. This may
be a text segment. In order to identify that we need the additional flag,
expose the target triple through the ObjectFileInfo as this information is lost
otherwise.
Since any modern ARM targeting environment on Windows would be Thumb-2 (Windows
ARM NT or Windows Embedded Compact), introducing a new flag to indicate the
section attribute seems to be a bit overkill. Simply depend on the target
triple. Since there is one location that this information is currently needed,
creating a target specific assembly parser and delegating the parsing of section
switches also feels a bit heavy handed. If it turns out that this information
ends up changing additional behaviour, then it may be worth considering that
alternative.
llvm-svn: 211481
User may initialize a var with non-zero value and specify .bss section.
E.g. : int a __attribute__((section(".bss"))) = 2;
This patch converts an assertion to error report for better user
experience.
Differential Revision: http://reviews.llvm.org/D4199
llvm-svn: 211455
This patch enables LLVM to emit Win64-native unwind info rather than
DWARF CFI. It handles all corner cases (I hope), including stack
realignment.
Because the unwind info is not flexible enough to describe stack frames
with a gap of unknown size in the middle, such as the one caused by
stack realignment, I modified register spilling code to place all spills
into the fixed frame slots, so that they can be accessed relative to the
frame pointer.
Patch by Vadim Chugunov!
Reviewed By: rnk
Differential Revision: http://reviews.llvm.org/D4081
llvm-svn: 211399
Use the MCStreamer base implementations for file ID tracking instead of
overriding them as no-ops.
Avoids assertions when streaming Dwarf debug info, and fixes ASM parsing of loc
and file directives.
llvm-svn: 211282
Currently, when using llvm as an assembler, DWARF debug information is only
generated for the .text section. This patch modifies this so that DWARF info
is emitted for all executable sections.
llvm-svn: 211273
Currently, llvm always emits a DWARF CIE with a version of 1, even when emitting
DWARF 3 or 4, which both support CIE version 3. This patch makes it emit the
newer CIE version when we are emitting DWARF 3 or 4. This will not reduce
compatibility, as we already emit other DWARF3/4 features, and is worth doing as
the DWARF3 spec removed some ambiguities in the interpretation of call frame
information.
It also fixes a minor bug where the "return address" field of the CIE was
encoded as a ULEB128, which is only valid when the CIE version is 3. There are
no test changes for this, because (as far as I can tell) none of the platforms
that we test have a return address register with a DWARF register number >127.
llvm-svn: 211272
We would get confused by '@' characters in symbol names, we would
mistake the text following them for the variant kind.
When an identifier a string, the variant kind will never show up inside
of it. Instead, check to see if there is a variant following the
string.
This fixes PR19965.
llvm-svn: 211249
ARMTargetStreamer implements ConstantPool and AssmeblerConstantPools
to keep track of assembler-generated constant pools that are used for
ldr-pseudo.
When implementing ldr-pseudo for AArch64, these two classes can be reused.
So this patch factors them out from ARM target to the general MC lib.
llvm-svn: 211198
Most Windows platforms use auxiliary data for unwinding. This information is
stored in the .pdata section. The encoding format for the data differs between
architectures and Windows variants. Windows MIPS and Alpha use identical
formats; Alpha64 is the same with different widths. Windows x86_64 and Itanium
share the representation. All Windows CE entries are identical irrespective of
the architecture. ARMv7 (Windows [NT] on ARM) has its own format.
This enumeration will become the differentiator once the windows EH emission
infrastructure is generalised, allowing us to emit the necessary unwinding
information for Windows on ARM.
llvm-svn: 210634
This reverts commit r206683.
The code was confusing SEH register numbers with DWARF register numbers.
The test case it was committed with was obviously incorrect. The
disassembler was roundtripping '.seh_pushreg %rsi' as '.seh_pushreg
%rbp', and other exciting things.
Noticed by Vadim Chugunov.
llvm-svn: 210574
I saw at least a memory leak or two from inspection (on probably
untested error paths) and r206991, which was the original inspiration
for this change.
I ran this idea by Jim Grosbach a few weeks ago & he was OK with it.
Since it's a basically mechanical patch that seemed sufficient - usual
post-commit review, revert, etc, as needed.
llvm-svn: 210427
link.exe requires that the text section has the IMAGE_SCN_MEM_16BIT flag set.
Otherwise, it will treat the function as ARM. If this occurs, then jumps to the
function will fail, switching from thumb to ARM mode execution.
With this change, it is possible to link using the MSVC linker as well.
llvm-svn: 210415
GAS documents the .type directive as having an optional comma following the key
symbol name when using the STT_<TYPE_IN_UPPER_CASE> form. However, it treats
the comma as optional in all cases. This makes the IAS support both forms of
inputs. Furthermore, the prefixed forms take either the upper case name or the
lower case alias.
The tests are split into two separate sets as the hash character serves as a
comment character on x86, which is tested in the second set by using arm-elf
which uses the at symbol as a comment character.
llvm-svn: 210407
This adjusts the section setup for the windows-itanium environment. This
environment does not report to be a known windows msvc environment, even though
it is (nearly) identical to the MSVC environment for C code.
llvm-svn: 210406
Add some whitespace, combine two sequential conditionals into a single one.
Reformat some section definitions to maintain uniformity in the function.
NFC.
llvm-svn: 210405
Prevent the early elimination of sections in the object writer. There may be
references to the section itself by other symbols, which may potentially not be
possible to resolve. ML (Visual Studio's Macro Assembler) also seems to retain
empty sections.
The elimination of symbols and sections which are unused should really occur at
the link phase. This will not cause any change in the resulting binary, simply
in the generated object files.
The adjustments to the other unit tests account for the fluctuating section
index caused by the appearance of sections which were previously discarded.
llvm-svn: 210373
* Section association cannot use just the section name as many
sections can have the same name. With this patch, the comdat symbol in
an assoc section is interpreted to mean a symbol in the associated
section and the mapping is discovered from it.
* Comdat symbols were not being set correctly. Instead we were getting
whatever was output first for that section.
A consequence is that associative sections now must use .section to
set the association. Using .linkonce would not work since it is not
possible to change a sections comdat symbol (it is used to decide if
we should create a new section or reuse an existing one).
This includes r210298, which was reverted because it was asserting
on an associated section having the same comdat as the associated
section.
llvm-svn: 210367
We extended the .section syntax to allow multiple sections with the
same name but different comdats, but currently we don't make sure that
the output section has that comdat symbol.
That happens to work with the code llc produces currently because it looks like
.section secName, "dr", one_only, "COMDATSym"
.globl COMDATSym
COMDATSym:
....
but that is not very friendly to anyone coding in assembly or even to
llc once we get comdat support in the IR.
This patch changes the coff object writer to make sure the comdat symbol is
output just after the section symbol, as required by the coff spec.
llvm-svn: 210298
For MIPS, we have to encode the personality routine with
an indirect pointer to absptr; otherwise, some link warning
warning will be raised, and the program might crash in some
early MIPS Android device.
llvm-svn: 209907
This commit starts with a "git mv ARM64 AArch64" and continues out
from there, renaming the C++ classes, intrinsics, and other
target-local objects for consistency.
"ARM64" test directories are also moved, and tests that began their
life in ARM64 use an arm64 triple, those from AArch64 use an aarch64
triple. Both should be equivalent though.
This finishes the AArch64 merge, and everyone should feel free to
continue committing as normal now.
llvm-svn: 209577
Now that clang can be used as an assembler via the IAS, invalid assembler inputs
would cause the assertions to trigger. Although we cannot recover from the
errors here, nor provide caret diagnostics, attempt to handle them slightly more
gracefully by reporting a fatal error.
llvm-svn: 209387
This reverts commit r208930, r208933, and r208975.
It seems not all fission consumers are ready to handle this behavior.
Reverting until tools are brought up to spec.
llvm-svn: 209338
Add support to allow a target specific COFF object writer to restrict the
recorded resolutions in the emitted object files. This is motivated by the need
in Windows on ARM, where an intermediate relocation needs to be prevented from
being emitted in the object file.
llvm-svn: 209336
Permit active macro expansions when terminating the assembler if there were
errors during the expansion. This would only trigger on invalid input when
built with assertions.
llvm-svn: 209309
The .drectve section should be marked as IMAGE_SCN_LNK_REMOVE. This matches what
the MSVC toolchain does and accurately reflects that this section should not be
emitted into the final binary. This section is merely information for the
linker, comprising of additional linker directives.
llvm-svn: 209273
Since type units in the dwo file are handled by a debug aware tool, they
don't need to leverage the ELF comdat grouping to implement
deduplication. Avoid creating all the .group sections for these as a
space optimization.
llvm-svn: 208930
fall back to the normal path without a cpu. While doing this fix
llc to just exit when we don't have a module to process instead of
asserting.
llvm-svn: 208102
The fix itself is fairly simple: move getAccessVariant to MCValue so that we
replace the old weak expression evaluation with the far more general
EvaluateAsRelocatable.
This then requires that EvaluateAsRelocatable stop when it finds a non
trivial reference kind. And that in turn requires the ELF writer to look
harder for weak references.
Last but not least, this found a case where we were being bug by bug
compatible with gas and accepting an invalid input. I reported pr19647
to track it.
llvm-svn: 207920
.file records are supposed to have a section identifier of 65534
(IMAGE_SCN_DEBUG) rather than 0. This is spelt out clearly within the PE/COFF
specification. Fix this minor oversight with the implementation for support for
.file records.
llvm-svn: 207851
This was initialized by llvm-mc (calling setDwarfVersion) but other
clients (such as clang, llc, etc) aren't necessarily initializing this
so we were getting garbage DWARF version values in the output.
Initialize it to a reasonable default (the same default used in llvm-mc,
though this is higher than it was (2) previously).
llvm-svn: 207788
This makes the coff writer compute the correct symbol value for the test in
pr19147. The section is still incorrect, that will be fixed in a followup patch.
llvm-svn: 207728
We already do this for shstrtab, so might as well do it for strtab. This
extracts the string table building code into a separate class. The idea
is to use it for other object formats too.
I mostly wanted to do this for the general principle, but it does save a
little bit on object file size. I tried this on a clang bootstrap and
saved 0.54% on the sum of object file sizes (1.14 MB out of 212 MB for
a release build).
Differential Revision: http://reviews.llvm.org/D3533
llvm-svn: 207670
This patch centralizes the handling of the thumb bit around
MCStreamer::isThumbFunc and makes isThumbFunc handle aliases.
This fixes a corner case, but the main advantage is having just one
way to check if a MCSymbol is thumb or not. This should still be
refactored to be ARM only, but at least now it is just one predicate
that has to be refactored instead of 3 (isThumbFunc,
ELF_Other_ThumbFunc, and SF_ThumbFunc).
llvm-svn: 207522
When evaluating an assembly expression for a relocation, we want to
stop at MCSymbols that are in the symbol table, even if they are variables.
This is needed since the semantics may require that the relocation use them.
That is not the case when computing the value of a symbol in the symbol table.
There are no relocations in this case and we have to keep going until we hit
a section or find out that the expression doesn't have an assembly time
value.
llvm-svn: 207445
The symbol table itself has no relocations, so it is not possible to represent
things like
a = undefined + 1
With the patch we just omit these variables. That matches the behaviour of the
gnu assembler.
llvm-svn: 207419
Only the object streamers need to track if a symbol should be marked thumb or
not. This ports the ELF case. The COFF case is not ported since it is currently
not working for some other reason (I will report a bug).
llvm-svn: 207366
This restores the previous behaviour of just assuming that if you dont specify a
valid triple that you really meant the default triple with an ELF object file.
llvm-svn: 207349
Introduce support for WoA PE/COFF object file emission from LLVM. Add the new
target specific PE/COFF Streamer (ARMWinCOFFStreamer) that handles the ARM
specific behaviour of PE/COFF object emission. ARM exception information is not
yet emitted and is a TODO item.
The ARM specific object writer (ARMWinCOFFObjectWriter) handles the ARM specific
relocation handling in conjunction with the WinCOFFObjectWriter in the MC layer.
The MC layer needs to be updated to deal with the relocation adjustments.
Branch relocations are adjusted by 4 bytes (unlikely their ELF counterparts).
Minor tweaks to switch multiple conditional checks into equivalent switch
statements. The ObjectFileInfo is updated to relax the object file setup for
Windows COFF. Move the architecture checks into an assertion. Windows COFF is
currently only supported on x86, x86_64, and ARM (thumb). Rather than
defaulting to ELF, we will refuse to generate an object file. This is better
though as you do not get an (arbitrary) object file which is different from the
request.
llvm-svn: 207345
This introduces a target specific streamer, X86WinCOFFStreamer, which handles
the target specific behaviour (e.g. WinEH). This is mostly to ensure that
differences between ARM and X86 remain disjoint and do not accidentally cross
boundaries. This is the final staging change for enabling object emission for
Windows on ARM.
llvm-svn: 207344
This is in preparation for promoting WinCOFFStreamer to a base class which will
be shared by the X86 and ARM specific target COFF streamers. Also add a new
getOrCreateSymbolData interface (like MCELFStreamer) for the ARM COFF Streamer.
This makes the COFFStreamer more similar to the ELFStreamer.
llvm-svn: 207343
Stylistic changes to prepare for splitting up the COFFStreamer into target
specific streamers. Tweak some assertion messages. No functional change.
llvm-svn: 207342
When fixing the symbols in each compressed section we were iterating
over all symbols for each compressed section. In extreme cases this
could snowball severely (5min uncompressed -> 35min compressed) due to
iterating over all symbols for each compressed section (large numbers of
compressed sections can be generated by DWARF type units).
To address this, build a map of the symbols in each section ahead of
time, and access that map if a section is being compressed. This brings
compile time for the aforementioned example down to ~6 minutes.
llvm-svn: 207167
