Now that we have a way to mark GlobalValues as local we can use the symbol
resolutions that the linker plugin provides as part of lto/thinlto link
step to refine the compilers view on what symbols will end up being local.
Originally commited as r317374, but reverted in r317395 to update some missed
tests.
Differential Revision: https://reviews.llvm.org/D35702
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Now that we have a way to mark GlobalValues as local we can use the symbol
resolutions that the linker plugin provides as part of lto/thinlto link
step to refine the compilers view on what symbols will end up being local.
Differential Revision: https://reviews.llvm.org/D35702
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@317374 91177308-0d34-0410-b5e6-96231b3b80d8
Not all targets support the use of absolute symbols to export
constants. In particular, ARM has a wide variety of constant encodings
that cannot currently be relocated by linkers. So instead of exporting
the constants using symbols, export them directly in the summary.
The values of the constants are left as zeroes on targets that support
symbolic exports.
This may result in more cache misses when targeting those architectures
as a result of arbitrary changes in constant values, but this seems
somewhat unavoidable for now.
Differential Revision: https://reviews.llvm.org/D37407
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Any unsuccessful llvm.type.checked.load devirtualizations will be translated
into uses of llvm.type.test, so we need to add the resulting llvm.type.test
intrinsics to the function summaries so that the LowerTypeTests pass will
export them.
Differential Revision: https://reviews.llvm.org/D29808
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A future change will cause this byte offset to be inttoptr'd and then exported
via an absolute symbol. On the importing end we will expect the symbol to be
in range [0,2^32) so that it will fit into a 32-bit relocation. The problem
is that on 64-bit architectures if the offset is negative it will not be in
the correct range once we inttoptr it.
This change causes us to use a 32-bit integer so that it can be inttoptr'd
(which zero extends) into the correct range.
Differential Revision: https://reviews.llvm.org/D30016
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Group calls into constant and non-constant arguments up front, and use uint64_t
instead of ConstantInt to represent constant arguments. The goal is to allow
the information from the summary to fit naturally into this data structure in
a future change (specifically, it will be added to CallSiteInfo).
This has two side effects:
- We disallow VCP for constant integer arguments of width >64 bits.
- We remove the restriction that the bitwidth of a vcall's argument and return
types must match those of the vfunc definitions.
I don't expect either of these to matter in practice. The first case is
uncommon, and the second one will lead to UB (so we can do anything we like).
Differential Revision: https://reviews.llvm.org/D29744
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It turns out that some of our negative tests were not in fact providing the
test coverage we expected: they were passing because the vtables were failing
an early check that they were constant. Fix this by changing the globals in
these tests to constants.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294550 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Keep track of all methods for which we have devirtualized at least
one call and then print them sorted alphabetically. That allows to
avoid duplicates and also makes the order deterministic.
Add optimization names into the remarks, so that it's easier to
understand how has each method been devirtualized.
Fix a bug when wrong methods could have been reported for
tryVirtualConstProp.
Reviewers: kcc, mehdi_amini
Differential Revision: https://reviews.llvm.org/D23297
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Summary:
Chrome on Linux uses WholeProgramDevirt for speed ups, and it's
important to detect regressions on both sides: the toolchain,
if fewer methods get devirtualized after an update, and Chrome,
if an innocently looking change caused many hot methods become
virtual again.
The need to track devirtualized methods is not Chrome-specific,
but it's probably the only user of the pass at this time.
Reviewers: kcc
Differential Revision: https://reviews.llvm.org/D23219
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Summary:
It's useful to have some visibility about which call sites are devirtualized,
especially for debug purposes. Another use case is a regression test on the
application side (like, Chromium).
Reviewers: pcc
Differential Revision: http://reviews.llvm.org/D22252
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This intrinsic safely loads a function pointer from a virtual table pointer
using type metadata. This intrinsic is used to implement control flow integrity
in conjunction with virtual call optimization. The virtual call optimization
pass will optimize away llvm.type.checked.load intrinsics associated with
devirtualized calls, thereby removing the type check in cases where it is
not needed to enforce the control flow integrity constraint.
This patch also introduces the capability to copy type metadata between
global variables, and teaches the virtual call optimization pass to do so.
Differential Revision: http://reviews.llvm.org/D21121
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The bitset metadata currently used in LLVM has a few problems:
1. It has the wrong name. The name "bitset" refers to an implementation
detail of one use of the metadata (i.e. its original use case, CFI).
This makes it harder to understand, as the name makes no sense in the
context of virtual call optimization.
2. It is represented using a global named metadata node, rather than
being directly associated with a global. This makes it harder to
manipulate the metadata when rebuilding global variables, summarise it
as part of ThinLTO and drop unused metadata when associated globals are
dropped. For this reason, CFI does not currently work correctly when
both CFI and vcall opt are enabled, as vcall opt needs to rebuild vtable
globals, and fails to associate metadata with the rebuilt globals. As I
understand it, the same problem could also affect ASan, which rebuilds
globals with a red zone.
This patch solves both of those problems in the following way:
1. Rename the metadata to "type metadata". This new name reflects how
the metadata is currently being used (i.e. to represent type information
for CFI and vtable opt). The new name is reflected in the name for the
associated intrinsic (llvm.type.test) and pass (LowerTypeTests).
2. Attach metadata directly to the globals that it pertains to, rather
than using the "llvm.bitsets" global metadata node as we are doing now.
This is done using the newly introduced capability to attach
metadata to global variables (r271348 and r271358).
See also: http://lists.llvm.org/pipermail/llvm-dev/2016-June/100462.html
Differential Revision: http://reviews.llvm.org/D21053
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This pass implements whole program optimization of virtual calls in cases
where we know (via bitset information) that the list of callees is fixed. This
includes the following:
- Single implementation devirtualization: if a virtual call has a single
possible callee, replace all calls with a direct call to that callee.
- Virtual constant propagation: if the virtual function's return type is an
integer <=64 bits and all possible callees are readnone, for each class and
each list of constant arguments: evaluate the function, store the return
value alongside the virtual table, and rewrite each virtual call as a load
from the virtual table.
- Uniform return value optimization: if the conditions for virtual constant
propagation hold and each function returns the same constant value, replace
each virtual call with that constant.
- Unique return value optimization for i1 return values: if the conditions
for virtual constant propagation hold and a single vtable's function
returns 0, or a single vtable's function returns 1, replace each virtual
call with a comparison of the vptr against that vtable's address.
Differential Revision: http://reviews.llvm.org/D16795
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