a Spectre v1 mitigation.
This was initially posted w/ the patch implementing this, got some basic
review there. Also, it is generated from a the Google doc that I shared
as part of the Speculative Load Hardening RFC and which has seen pretty
widespread review at this point.
However, as the patches are landing in LLVM, I wanted to land the docs
as well. But it seemed like a bad idea to have them in the same commit
in case of reverts or other things. So the docs are split out here.
Thanks for all the review so far, and further review and improvements to
the documentation here welcome. Please feel free to keep hammering on
the code review or Google document.
Note that this is a markdown document which Sphinx doesn't yet process.
But we can add support for that after and this should get picked up
(and I'm preparing patches for that). Also, this gets the document
itself into a nice shared place where we can iterate on it.
Differential Revision: https://reviews.llvm.org/D49433
llvm-svn: 337391
We need to explicitly state what happens when an invariant promised by
load metadata is violated at runtime, since it's come up repeatedly.
It's possible we want to specify that the result of the load is poison
in some cases, rather than undefined behavior, if the constraint is
violated. That would allow preserving the metadata when the load is
hoisted, but doesn't allow propagating metadata based on control flow.
We currently do transforms based on control flow for nonnull metadata
(in PromoteMemToReg).
Differential Revision: https://reviews.llvm.org/D47854
llvm-svn: 337325
Clarify that violating nnan and ninf can lead to undefined behavior.
This allows more aggressive optimizations based on those assumptions.
Differential Revision: https://reviews.llvm.org/D47963
llvm-svn: 337323
We're going to work on this in a separate review focusing more on documenting
the View and probably removing some of the less-interesting/less-useful pieces.
This reverts r337219,337225
llvm-svn: 337295
As discussed here:
http://lists.llvm.org/pipermail/llvm-dev/2018-May/123292.htmlhttp://lists.llvm.org/pipermail/llvm-dev/2018-July/124400.html
We want to add rotate intrinsics because the IR expansion of that pattern is 4+ instructions,
and we can lose pieces of the pattern before it gets to the backend. Generalizing the operation
by allowing 2 different input values (plus the 3rd shift/rotate amount) gives us a "funnel shift"
operation which may also be a single hardware instruction.
Initially, I thought we needed to define new DAG nodes for these ops, and I spent time working
on that (much larger patch), but then I concluded that we don't need it. At least as a first
step, we have all of the backend support necessary to match these ops...because it was required.
And shepherding these through the IR optimizer is the primary concern, so the IR intrinsics are
likely all that we'll ever need.
There was also a question about converting the intrinsics to the existing ROTL/ROTR DAG nodes
(along with improving the oversized shift documentation). Again, I don't think that's strictly
necessary (as the test results here prove). That can be an efficiency improvement as a small
follow-up patch.
So all we're left with is documentation, definition of the IR intrinsics, and DAG builder support.
Differential Revision: https://reviews.llvm.org/D49242
llvm-svn: 337221
This patch introduces a brief description of the components of MCA. The main
focus is on Views. This is a work in progress, and more descriptions will be
introduced later. I want to flesh-out the Views section more and provide a
detailed description of eventing in MCA. Eventually a brief code example of a
View should accompany the description.
Also, we should consider moving the MCA internals guide elsewhere at some point.
llvm-svn: 337219
As suggested in the review for r337007, this makes cfi-verify abort on unsupported targets instead of producing incorrect results. It also updates the design document to reflect this.
Differential Revision: https://reviews.llvm.org/D49304
llvm-svn: 337181
-v prints all directive pattern matches.
-vv additionally prints info that might be noise to users but that can
be helpful to FileCheck developers.
To maximize code reuse and to make diagnostics more consistent, this
patch also adjusts and extends some of the existing diagnostics.
CHECK-NOT failures now report variables uses. Many more diagnostics
now report the check prefix and kind of directive.
Reviewed By: probinson
Differential Revision: https://reviews.llvm.org/D47114
llvm-svn: 336967
That is, make CHECK-DAG skip matches that overlap the matches of any
preceding consecutive CHECK-DAG directives. This change makes
CHECK-DAG more consistent with other directives, and there is evidence
it makes CHECK-DAG more intuitive and less error-prone. See the RFC
discussion starting at:
http://lists.llvm.org/pipermail/llvm-dev/2018-May/123010.html
Moreover, this behavior enables CHECK-DAG groups for unordered,
non-unique strings or patterns. For example, it is useful for
verifying output or logs from a parallel program, such as the OpenMP
runtime.
This patch also implements the command-line option
-allow-deprecated-dag-overlap, which reverts CHECK-DAG to the old
overlapping behavior. This option should not be used in new tests.
It is meant only for the existing tests that are broken by this change
and that need time to update.
See the following bugzilla issue for tracking of such tests:
https://bugs.llvm.org/show_bug.cgi?id=37532
Patches to add -allow-deprecated-dag-overlap to those tests will
follow immediately.
Reviewed By: probinson
Differential Revision: https://reviews.llvm.org/D47106
llvm-svn: 336847
This reverts commit r306102.
This change was made without any review, and has a couple of issues.
First, AFAIK we do not test the combination of the LLVM gold plugin with
ld.bfd. Second, the change removed documentation for how to build gold
and replaced it with instructions for building ld.bfd.
llvm-svn: 336841
That is, make CHECK-DAG skip matches that overlap the matches of any
preceding consecutive CHECK-DAG directives. This change makes
CHECK-DAG more consistent with other directives, and there is evidence
it makes CHECK-DAG more intuitive and less error-prone. See the RFC
discussion starting at:
http://lists.llvm.org/pipermail/llvm-dev/2018-May/123010.html
Moreover, this behavior enables CHECK-DAG groups for unordered,
non-unique strings or patterns. For example, it is useful for
verifying output or logs from a parallel program, such as the OpenMP
runtime.
This patch also implements the command-line option
-allow-deprecated-dag-overlap, which reverts CHECK-DAG to the old
overlapping behavior. This option should not be used in new tests.
It is meant only for the existing tests that are broken by this change
and that need time to update.
See the following bugzilla issue for tracking of such tests:
https://bugs.llvm.org/show_bug.cgi?id=37532
Patches to add -allow-deprecated-dag-overlap to those tests will
follow immediately.
Reviewed By: probinson
Differential Revision: https://reviews.llvm.org/D47106
llvm-svn: 336830
The aim of this backend is to output everything TableGen knows about
the record set, similarly to the default -print-records backend. But
where -print-records produces output in TableGen's input syntax
(convenient for humans to read), this backend produces it as
structured JSON data, which is convenient for loading into standard
scripting languages such as Python, in order to extract information
from the data set in an automated way.
The output data contains a JSON representation of the variable
definitions in output 'def' records, and a few pieces of metadata such
as which of those definitions are tagged with the 'field' prefix and
which defs are derived from which classes. It doesn't dump out
absolutely every piece of knowledge it _could_ produce, such as type
information and complicated arithmetic operator nodes in abstract
superclasses; the main aim is to allow consumers of this JSON dump to
essentially act as new backends, and backends don't generally need to
depend on that kind of data.
The new backend is implemented as an EmitJSON() function similar to
all of llvm-tblgen's other EmitFoo functions, except that it lives in
lib/TableGen instead of utils/TableGen on the basis that I'm expecting
to add it to clang-tblgen too in a future patch.
To test it, I've written a Python script that loads the JSON output
and tests properties of it based on comments in the .td source - more
or less like FileCheck, except that the CHECK: lines have Python
expressions after them instead of textual pattern matches.
Reviewers: nhaehnle
Reviewed By: nhaehnle
Subscribers: arichardson, labath, mgorny, llvm-commits
Differential Revision: https://reviews.llvm.org/D46054
llvm-svn: 336771
Let's be conservative here; it matches what we actually implemented, and
it should be rare in practice anyway.
Differential Revision: https://reviews.llvm.org/D49042
llvm-svn: 336744
Summary:
Support for this option is needed for building Linux kernel.
This is a very frequently requested feature by kernel developers.
More details : https://lkml.org/lkml/2018/4/4/601
GCC option description for -fdelete-null-pointer-checks:
This Assume that programs cannot safely dereference null pointers,
and that no code or data element resides at address zero.
-fno-delete-null-pointer-checks is the inverse of this implying that
null pointer dereferencing is not undefined.
This feature is implemented in LLVM IR in this CL as the function attribute
"null-pointer-is-valid"="true" in IR (Under review at D47894).
The CL updates several passes that assumed null pointer dereferencing is
undefined to not optimize when the "null-pointer-is-valid"="true"
attribute is present.
Reviewers: t.p.northover, efriedma, jyknight, chandlerc, rnk, srhines, void, george.burgess.iv
Reviewed By: efriedma, george.burgess.iv
Subscribers: eraman, haicheng, george.burgess.iv, drinkcat, theraven, reames, sanjoy, xbolva00, llvm-commits
Differential Revision: https://reviews.llvm.org/D47895
llvm-svn: 336613
In non-zero address spaces, we were reporting that an object at `null`
always occupies zero bytes. This is incorrect in many cases, so just
return `unknown` in those cases for now.
Differential Revision: https://reviews.llvm.org/D48860
llvm-svn: 336611
Summary:
This adds a new -no-weak flag to nm to hide weak symbols in its output.
This also adds a -W alias for this which is analogous to -U.
Patch by Keith Smiley
Reviewers: kastiglione, enderby, compnerd
Reviewed By: kastiglione
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D48751
llvm-svn: 336126
Summary:
This patch introduce new intrinsic -
strip.invariant.group that was described in the
RFC: Devirtualization v2
Reviewers: rsmith, hfinkel, nlopes, sanjoy, amharc, kuhar
Subscribers: arsenm, nhaehnle, JDevlieghere, hiraditya, xbolva00, llvm-commits
Differential Revision: https://reviews.llvm.org/D47103
Co-authored-by: Krzysztof Pszeniczny <krzysztof.pszeniczny@gmail.com>
llvm-svn: 336073
Prior to this change, there was no clean way of getting FileCheck to
check that a line is completely empty. The expected way of using
"CHECK: {{^$}}" does not work because the '^' matches the end of the
previous match (this behaviour may be desirable in certain instances).
For the same reason, "CHECK-NEXT: {{^$}}" will fail when the previous
match was at the end of the line, as the pattern will match there.
Using the recommended [[:space:]] to match an explicit new line could
also match a space, and thus is not always desired. Literal '\n'
matches also do not work. A workaround was suggested in the review, but
it is a little clunky.
This change adds a new directive that behaves the same as CHECK-NEXT,
except that it only matches against empty lines (nothing, not even
whitespace, is allowed). As with CHECK-NEXT, it will fail if more than
one newline occurs before the next blank line. Example usage:
; test.txt
foo
bar
; CHECK: foo
; CHECK-EMPTY:
; CHECK-NEXT: bar
Differential Revision: https://reviews.llvm.org/D28896
Reviewed by: probinson
llvm-svn: 335613
Update AMDGPU assembler syntax behind the code-object-v3 feature:
* Replace/rename most AMDGPU assembler directives/symbols and document them.
* Provide more diagnostics (e.g. values out of range, missing values, repeated
values).
* Provide path for backwards compatibility, even with underlying descriptor
changes.
Differential Revision: https://reviews.llvm.org/D47736
llvm-svn: 335281
and everything that comes with it from implementation
and v3 header files.
Leave definition in v2 header files for backwards
compatibility.
Differential Revision: https://reviews.llvm.org/D48191
llvm-svn: 335267
Summary:
This is essentially a rewrite of the backend which introduces TableGen
base classes GenericEnum, GenericTable, and SearchIndex. They allow
generating custom enums and tables with lookup functions using
separately defined records as the underlying database.
Also added as part of this change:
- Lookup functions may use indices composed of multiple fields.
- Instruction fields are supported similar to Intrinsic fields.
- When the lookup key has contiguous numeric values, the lookup
function will directly index into the table instead of using a binary
search.
The existing SearchableTable functionality is internally mapped to the
new primitives.
Change-Id: I444f3490fa1dbfb262d7286a1660a2c4308e9932
Reviewers: arsenm, tra, t.p.northover
Subscribers: wdng, llvm-commits
Differential Revision: https://reviews.llvm.org/D48013
llvm-svn: 335225
IEEE 754 defines the expected result on overflow. As far as I know,
hardware implementations (of f16), and compiler-rt (__floatuntisf)
correctly return +-Inf on overflow. And I can't think of any useful
transform that would take advantage of overflow being undefined here.
Differential Revision: https://reviews.llvm.org/D47807
llvm-svn: 334777
- Do not emit following assembler directives:
- .hsa_code_object_version
- .hsa_code_object_isa
- .amd_amdgpu_isa
- .amd_amdgpu_hsa_metadata
- .amd_amdgpu_pal_metadata
- Do not emit .note entries
- Cleanup and bring in sync kernel descriptor header file
- Emit kernel descriptor into .rodata with appropriate relocations and
alignments
llvm-svn: 334519
I think we assume poison, not undef, for certain transforms we
currently do. In any case, we should clarify the language here.
(This sort of conversion is undefined behavior according to the C
and C++ standards. And in practice, hardware implementations handle
overflow inconsistently, so it would be difficult to define the
result here.)
Differential Revision: https://reviews.llvm.org/D47851
llvm-svn: 334326
We need to clarify the language here. I think poison makes more sense
than undef, since it's an undefined operation rather than uninitialized
memory. I don't think anything depends on the difference at the moment,
though.
Differential Revision: https://reviews.llvm.org/D47859
llvm-svn: 334325
since couple of months, supports had been enabled for FreeBSD and OpenBSD.
Reviewers: thakis, spatel, dim
Reviewed By: dim
Differential Revision: https://reviews.llvm.org/D47322
llvm-svn: 334207
Summary: It has been deprecated in favor of SETCCCARRY for a year now and isn't used by any in tree backend.
Reviewers: efriedma, craig.topper, dblaikie, bkramer
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D47685
llvm-svn: 333939
Summary:
The new rules are straightforward. The main rules to keep in mind
are:
1. NAME is an implicit template argument of class and multiclass,
and will be substituted by the name of the instantiating def/defm.
2. The name of a def/defm in a multiclass must contain a reference
to NAME. If such a reference is not present, it is automatically
prepended.
And for some additional subtleties, consider these:
3. defm with no name generates a unique name but has no special
behavior otherwise.
4. def with no name generates an anonymous record, whose name is
unique but undefined. In particular, the name won't contain a
reference to NAME.
Keeping rules 1&2 in mind should allow a predictable behavior of
name resolution that is simple to follow.
The old "rules" were rather surprising: sometimes (but not always),
NAME would correspond to the name of the toplevel defm. They were
also plain bonkers when you pushed them to their limits, as the old
version of the TableGen test case shows.
Having NAME correspond to the name of the toplevel defm introduces
"spooky action at a distance" and breaks composability:
refactoring the upper layers of a hierarchy of nested multiclass
instantiations can cause unexpected breakage by changing the value
of NAME at a lower level of the hierarchy. The new rules don't
suffer from this problem.
Some existing .td files have to be adjusted because they ended up
depending on the details of the old implementation.
Change-Id: I694095231565b30f563e6fd0417b41ee01a12589
Reviewers: tra, simon_tatham, craig.topper, MartinO, arsenm, javed.absar
Subscribers: wdng, llvm-commits
Differential Revision: https://reviews.llvm.org/D47430
llvm-svn: 333900
Object FIle Representation
At codegen time this is emitted into the ELF file a pair of symbol indices and a weight. In assembly it looks like:
.cg_profile a, b, 32
.cg_profile freq, a, 11
.cg_profile freq, b, 20
When writing an ELF file these are put into a SHT_LLVM_CALL_GRAPH_PROFILE (0x6fff4c02) section as (uint32_t, uint32_t, uint64_t) tuples as (from symbol index, to symbol index, weight).
Differential Revision: https://reviews.llvm.org/D44965
llvm-svn: 333823
