`sign-return-address` and similar module attributes should be propagated
to the function level before modules got merged because module flags may
contradict and this information is not recoverable.
Generated code will match with the normal linking flow.
NOTE: For brevity the following talks about ConstantInt but
everything extends to cover ConstantFP as well.
Whilst ConstantInt::get() supports the creation of vectors whereby
each lane has the same value, it achieves this via other constants:
* ConstantVector for fixed-length vectors
* ConstantExprs for scalable vectors
However, ConstantExprs are being deprecated and ConstantVector is
not space efficient for larger vector types. By extending ConstantInt
we can represent vector splats by only storing the underlying scalar
value.
More specifically:
* ConstantInt gains an ElementCount variant of get().
* LLVMContext is extended to map <EC,APInt>->ConstantInt.
* BitcodeReader/Writer support is extended to allow vector types.
Whilst this patch adds the base support, more work is required
before it's production ready. For example, there's likely to be
many places where isa<ConstantInt> assumes a scalar type. Accordingly
the default behaviour of ConstantInt::get() remains unchanged but a
set of flags are added to allow wider testing and thus help with the
migration:
--use-constant-int-for-fixed-length-splat
--use-constant-fp-for-fixed-length-splat
--use-constant-int-for-scalable-splat
--use-constant-fp-for-scalable-splat
NOTE: No change is required to the bitcode format because types and
values are handled separately.
NOTE: For similar reasons as above, code generation doesn't work
out-the-box.
We've been building and testing this no-debug-intrinsic work inside of
the pass manager for a while, so that optimisation passes get exercised
and tested when we turn it on. However, by converting to the
non-intrinsic form in the bitcode loader, we accidentally caused all
parts of LLVM to potentially see non-intrinsic debug-info.
Seeing how we're trying to turn things on incrementally, it was a
mistake to go this far this fast: we can instead just focus on enabling
during optimisations for the moment, then all the other parts of LLVM
later.
Turns out I was using DbgMarker::getDbgValueRange rather than the helper
utility in Instruction::getDbgValueRange, which checks for null-ness.
Original commit message follows.
[DebugInfo][RemoveDIs] Convert debug-info modes when loading bitcode (#78967)
As part of eliminating debug-intrinsics in LLVM, we'll shortly be
pushing the conversion from "old" dbg.value mode to "new" DPValue mode
out from when the pass manager runs, to when modules are loaded. This
patch adds that conversion process and some (temporary) options to
llvm-lto{,2} to help test it.
Specifically: now whenever we load a bitcode module, consider a flag of
whether to "upgrade" it into the new debug-info mode, and if we're
lazily materializing functions then do that lazily too. Doing this
exposes an error in the IRLinker/materializer handling of DPValues,
where we need to transfer the debug-info format flag correctly, and in
ValueMapper we need to remap the Values that DPValues point at.
I've added some test coverage in the modified tests; these will be
exercised by our llvm-new-debug-iterators buildbot.
This upgrading of debug-info won't be happening for the llvm18 release,
instead we'll turn it on after the branch date, thenbe push the boundary
of where "new" debug-info starts and ends down into the existing
debug-info upgrade path over the course of the next release.
As part of eliminating debug-intrinsics in LLVM, we'll shortly be
pushing the conversion from "old" dbg.value mode to "new" DPValue mode
out from when the pass manager runs, to when modules are loaded. This
patch adds that conversion process and some (temporary) options to
llvm-lto{,2} to help test it.
Specifically: now whenever we load a bitcode module, consider a flag of
whether to "upgrade" it into the new debug-info mode, and if we're
lazily materializing functions then do that lazily too. Doing this
exposes an error in the IRLinker/materializer handling of DPValues,
where we need to transfer the debug-info format flag correctly, and in
ValueMapper we need to remap the Values that DPValues point at.
I've added some test coverage in the modified tests; these will be
exercised by our llvm-new-debug-iterators buildbot.
This upgrading of debug-info won't be happening for the llvm18 release,
instead we'll turn it on after the branch date, thenbe push the boundary
of where "new" debug-info starts and ends down into the existing
debug-info upgrade path over the course of the next release.
Add the `dead_on_unwind` attribute, which states that the caller will
not read from this argument if the call unwinds. This allows eliding
stores that could otherwise be visible on the unwind path, for example:
```
declare void @may_unwind()
define void @src(ptr noalias dead_on_unwind %out) {
store i32 0, ptr %out
call void @may_unwind()
store i32 1, ptr %out
ret void
}
define void @tgt(ptr noalias dead_on_unwind %out) {
call void @may_unwind()
store i32 1, ptr %out
ret void
}
```
The optimization is not valid without `dead_on_unwind`, because the `i32
0` value might be read if `@may_unwind` unwinds.
This attribute is primarily intended to be used on sret arguments. In
fact, I previously wanted to change the semantics of sret to include
this "no read after unwind" property (see D116998), but based on the
feedback there it is better to keep these attributes orthogonal (sret is
an ABI attribute, dead_on_unwind is an optimization attribute). This is
a reboot of that change with a separate attribute.
This adds support for a HasTailCall flag on function call edges in the
ThinLTO summary. It is intended for use in aiding discovery of missing
frames from tail calls in profiled call stacks for MemProf of profiled
binaries that did not disable tail call elimination. A follow on change
will add the use of this new flag during MemProf context disambiguation.
The new flag is encoded in the bitcode along with either the hotness
flag from the profile, or the relative block frequency under the
-write-relbf-to-summary flag when there is no profile data.
Because we now will always have some additional call edge information, I
have removed the non-profile function summary record format, and we
simply encode the tail call flag along with a hotness type of none when
there is no profile information or relative block frequency. The change
of record format and name caused most of the test case changes.
I have added explicit testing of generation of the new tail call flag
into the bitcode and IR assembly format as part of the changes to
llvm/test/Bitcode/thinlto-function-summary-refgraph.ll. I have also
added round trip testing through assembly and bitcode to
llvm/test/Assembler/thinlto-summary.ll.
This flag indicates that every bit is known to be zero in at least one
of the inputs. This allows the Or to be treated as an Add since there is
no possibility of a carry from any bit.
If the flag is present and this property does not hold, the result is
poison.
This makes it easier to reverse the InstCombine transform that turns Add
into Or.
This is inspired by a comment here
https://github.com/llvm/llvm-project/pull/71955#discussion_r1391614578
Discourse thread
https://discourse.llvm.org/t/rfc-add-or-disjoint-flag/75036
Close https://github.com/llvm/llvm-project/issues/56980.
This patch tries to introduce a light-weight optimization attribute for
coroutines which are guaranteed to only be destroyed after it reached
the final suspend.
The rationale behind the patch is simple. See the example:
```C++
A foo() {
dtor d;
co_await something();
dtor d1;
co_await something();
dtor d2;
co_return 43;
}
```
Generally the generated .destroy function may be:
```C++
void foo.destroy(foo.Frame *frame) {
switch(frame->suspend_index()) {
case 1:
frame->d.~dtor();
break;
case 2:
frame->d.~dtor();
frame->d1.~dtor();
break;
case 3:
frame->d.~dtor();
frame->d1.~dtor();
frame->d2.~dtor();
break;
default: // coroutine completed or haven't started
break;
}
frame->promise.~promise_type();
delete frame;
}
```
Since the compiler need to be ready for all the cases that the coroutine
may be destroyed in a valid state.
However, from the user's perspective, we can understand that certain
coroutine types may only be destroyed after it reached to the final
suspend point. And we need a method to teach the compiler about this.
Then this is the patch. After the compiler recognized that the
coroutines can only be destroyed after complete, it can optimize the
above example to:
```C++
void foo.destroy(foo.Frame *frame) {
frame->promise.~promise_type();
delete frame;
}
```
I spent a lot of time experimenting and experiencing this in the
downstream. The numbers are really good. In a real-world coroutine-heavy
workload, the size of the build dir (including .o files) reduces 14%.
And the size of final libraries (excluding the .o files) reduces 8% in
Debug mode and 1% in Release mode.
Remove support for zext and sext constant expressions. All places
creating them have been removed beforehand, so this just removes the
APIs and uses of these constant expressions in tests.
There is some additional cleanup that can be done on top of this, e.g.
we can remove the ZExtInst vs ZExtOperator footgun.
This is part of
https://discourse.llvm.org/t/rfc-remove-most-constant-expressions/63179.
This adds a writable attribute, which in conjunction with
dereferenceable(N) states that a spurious store of N bytes is
introduced on function entry. This implies that this many bytes
are writable without trapping or introducing data races. See
https://llvm.org/docs/Atomics.html#optimization-outside-atomic for
why the second point is important.
This attribute can be added to sret arguments. I believe Rust will
also be able to use it for by-value (moved) arguments. Rust likely
won't be able to use it for &mut arguments (tree borrows does not
appear to allow spurious stores).
In this patch the new attribute is only used by LICM scalar promotion.
However, the actual motivation for this is to fix a correctness issue
in call slot optimization, which needs this attribute to avoid
optimization regressions.
Followup to the discussion on D157499.
Differential Revision: https://reviews.llvm.org/D158081
Add an nneg flag to the zext instruction, which specifies that the
argument is non-negative. Otherwise, the result is a poison value.
The primary use-case for the flag is to preserve information when sext
gets replaced with zext due to range-based canonicalization. The nneg
flag allows us to convert the zext back into an sext later. This is
useful for some optimizations (e.g. a signed icmp can fold with sext but
not zext), as well as some targets (e.g. RISCV prefers sext over zext).
Discourse thread: https://discourse.llvm.org/t/rfc-add-zext-nneg-flag/73914
This patch is based on https://reviews.llvm.org/D156444 by
@Panagiotis156, with some implementation simplifications and additional
tests.
---------
Co-authored-by: Panagiotis K <karouzakispan@gmail.com>
This patch adds a new fn attribute, `optdebug`, that specifies that
optimizations should make decisions that prioritize debug info quality,
potentially at the cost of runtime performance.
This patch does not add any functional changes triggered by this
attribute, only the attribute itself. A subsequent patch will use this
flag to disable the post-RA scheduler.
Metadata (via ValueAsMetadata) can reference constant expressions
that may no longer be supported. These references can both be in
function-local metadata and module metadata, if the same expression
is used in multiple functions. At least in theory, such references
could also be in metadata proper, rather than just inside
ValueAsMetadata references in calls.
Instead of trying to expand these expressions (which we can't
reliably do), pretend that the constant has been deleted, which
means that ValueAsMetadata references will get replaced with
undef metadata.
Fixes https://github.com/llvm/llvm-project/issues/68281.
This fixes the bitcode upgrade failure reported in
https://reviews.llvm.org/D155924#4616789.
The expansion always happens in the entry block, so this may be
inaccurate if there are trapping constant expressions.
The module paths string table mapped to both an id sequentially assigned
during LTO linking, and the module hash. The former is leftover from
before the module hash was added for caching and subsequently replaced
use of the module id when renaming promoted symbols (to avoid affects
due to link order changes). The sequentially assigned module id was not
removed, however, as it was still a convenience when serializing to/from
bitcode and assembly.
This patch removes the module id from this table, since it isn't
strictly needed and can lead to confusion on when it is appropriate to
use (e.g. see fix in D156525). It also takes a (likely not significant)
amount of overhead. Where an integer module id is needed (e.g. bitcode
writing), one is assigned on the fly.
There are a couple of test changes since the paths are now sorted
alphanumerically when assigning ids on the fly during assembly writing,
in order to ensure deterministic behavior.
Differential Revision: https://reviews.llvm.org/D156730
Here's a high level summary of the changes in this patch. For more
information on rational, see the RFC.
(https://discourse.llvm.org/t/rfc-a-unified-lto-bitcode-frontend/61774).
- Add config parameter to LTO backend, specifying which LTO mode is
desired when using unified LTO.
- Add unified LTO flag to the summary index for efficiency. Unified
LTO modules can be detected without parsing the module.
- Make sure that the ModuleID is generated by incorporating more types
of symbols.
Differential Revision: https://reviews.llvm.org/D123803
Move `AttributeMask` out of `llvm/IR/Attributes.h` to a new file
`llvm/IR/AttributeMask.h`. After doing this we can remove the
`#include <bitset>` and `#include <set>` directives from `Attributes.h`.
Since there are many headers including `Attributes.h`, but not needing
the definition of `AttributeMask`, this causes unnecessary bloating of
the translation units and slows down compilation.
This commit adds in the include directive for `llvm/IR/AttributeMask.h`
to the handful of source files that need to see the definition.
This reduces the total number of preprocessing tokens across the LLVM
source files in lib from (roughly) 1,917,509,187 to 1,902,982,273 - a
reduction of ~0.76%. This should result in a small improvement in
compilation time.
Differential Revision: https://reviews.llvm.org/D153728
Adds an LTO option to indicate that whether we are linking with an
allocator that supports hot/cold operator new interfaces. If not,
at the start of the LTO backends any existing memprof hot/cold
attributes are removed from the IR, and we also remove memprof metadata
so that post-LTO inlining doesn't add any new attributes.
This is done via setting a new flag in the module summary index. It is
important to communicate via the index to the LTO backends so that
distributed ThinLTO handles this correctly, as they are invoked by
separate clang processes and the combined index is how we communicate
information from the LTO link. Specifically, for distributed ThinLTO the
LTO related processes look like:
```
# Thin link:
$ lld --thinlto-index-only obj1.o ... objN.o -llib ...
# ThinLTO backends:
$ clang -x ir obj1.o -fthinlto-index=obj1.o.thinlto.bc -c -O2
...
$ clang -x ir objN.o -fthinlto-index=objN.o.thinlto.bc -c -O2
```
It is during the thin link (lld --thinlto-index-only) that we have
visibility into linker dependences and want to be able to pass the new
option via -Wl,-supports-hot-cold-new. This will be recorded in the
summary indexes created for the distributed backend processes
(*.thinlto.bc) and queried from there, so that we don't need to know
during those individual clang backends what allocation library was
linked. Since in-process ThinLTO and regular LTO also use a combined
index, for consistency we query the flag out of the index in all LTO
backends.
Additionally, when the LTO option is disabled, exit early from the
MemProfContextDisambiguation handling performed during LTO, as this is
unnecessary.
Depends on D149117 and D149192.
Differential Revision: https://reviews.llvm.org/D149215
This carries a bitmask indicating forbidden floating-point value kinds
in the argument or return value. This will enable interprocedural
-ffinite-math-only optimizations. This is primarily to cover the
no-nans and no-infinities cases, but also covers the other floating
point classes for free. Textually, this provides a number of names
corresponding to bits in FPClassTest, e.g.
call nofpclass(nan inf) @must_be_finite()
call nofpclass(snan) @cannot_be_snan()
This is more expressive than the existing nnan and ninf fast math
flags. As an added bonus, you can represent fun things like nanf:
declare nofpclass(inf zero sub norm) float @only_nans()
Compared to nnan/ninf:
- Can be applied to individual call operands as well as the return value
- Can distinguish signaling and quiet nans
- Distinguishes the sign of infinities
- Can be safely propagated since it doesn't imply anything about
other operands.
- Does not apply to FP instructions; it's not a flag
This is one step closer to being able to retire "no-nans-fp-math" and
"no-infs-fp-math". The one remaining situation where we have no way to
represent no-nans/infs is for loads (if we wanted to solve this we
could introduce !nofpclass metadata, following along with
noundef/!noundef).
This is to help simplify the GPU builtin math library
distribution. Currently the library code has explicit finite math only
checks, read from global constants the compiler driver needs to set
based on the compiler flags during linking. We end up having to
internalize the library into each translation unit in case different
linked modules have different math flags. By propagating known-not-nan
and known-not-infinity information, we can automatically prune the
edge case handling in most functions if the function is only reached
from fast math uses.
This patch adds several missing GlobalList modifier functions, like
removeGlobalVariable(), eraseGlobalVariable() and insertGlobalVariable().
There is no longer need to access the list directly so it also makes
getGlobalList() private.
Differential Revision: https://reviews.llvm.org/D144027
These are essentially add/sub 1 with a clamping value.
AMDGPU has instructions for these. CUDA/HIP expose these as
atomicInc/atomicDec. Currently we use target intrinsics for these,
but those do no carry the ordering and syncscope. Add these to
atomicrmw so we can carry these and benefit from the regular
legalization processes.
When opaque pointers are enabled and old IR with typed pointers is read,
the BitcodeReader automatically upgrades all typed pointers to opaque
pointers. This is a lossy conversion, i.e. when a function argument is a
pointer and unused, it’s impossible to reconstruct the original type
behind the pointer.
There are cases where the type information of pointers is needed. One is
reading DXIL, which is bitcode of old LLVM IR and makes a lot of use of
pointers in function signatures.
We’d like to keep using up-to-date llvm to read in and process DXIL, so
in the face of opaque pointers, we need some way to access the type
information of pointers from the read bitcode.
This patch allows extracting type information by supplying functions to
parseBitcodeFile that get called for each function signature or metadata
value. The function can access the type information via the reader’s
type IDs and the getTypeByID and getContainedTypeID functions.
The tests exemplarily shows how type info from pointers can be stored in
metadata for use after the BitcodeReader finished.
Differential Revision: https://reviews.llvm.org/D127728
This reverts commit b56df190b01335506ce30a4559d880da76d1a181.
The unit tests are implemented in a way that requires support for
writing typed pointer bitcode, which is going away soon. Please
rewrite it in a way that not have requirement, e.g. by shipping
pre-compiled bitcode, as we do for integration tests.
When opaque pointers are enabled and old IR with typed pointers is read,
the BitcodeReader automatically upgrades all typed pointers to opaque
pointers. This is a lossy conversion, i.e. when a function argument is a
pointer and unused, it’s impossible to reconstruct the original type
behind the pointer.
There are cases where the type information of pointers is needed. One is
reading DXIL, which is bitcode of old LLVM IR and makes a lot of use of
pointers in function signatures.
We’d like to keep using up-to-date llvm to read in and process DXIL, so
in the face of opaque pointers, we need some way to access the type
information of pointers from the read bitcode.
This patch allows extracting type information by supplying functions to
parseBitcodeFile that get called for each function signature or metadata
value. The function can access the type information via the reader’s
type IDs and the getTypeByID and getContainedTypeID functions.
The tests exemplarily shows how type info from pointers can be stored in
metadata for use after the BitcodeReader finished.
Differential Revision: https://reviews.llvm.org/D127728
Use the existing mechanism to change the data layout using callbacks.
Before this patch, we had a callback type DataLayoutCallbackTy that receives
a single StringRef specifying the target triple, and optionally returns
the data layout string to be used. Module loaders (both IR and BC) then
apply the callback to potentially override the module's data layout,
after first having imported and parsed the data layout from the file.
We can't do the same to fix invalid data layouts, because the import will already
fail, before the callback has a chance to fix it.
Instead, module loaders now tentatively parse the data layout into a string,
wait until the target triple has been parsed, apply the override callback
to the imported string and only then parse the tentative string as a data layout.
Moreover, add the old data layout string S as second argument to the callback,
in addition to the already existing target triple argument.
S is either the default data layout string in case none is specified, or the data
layout string specified in the module, possibly after auto-upgrades (for the BitcodeReader).
This allows callbacks to inspect the old data layout string,
and fix it instead of setting a fixed data layout.
Also allow to pass data layout override callbacks to lazy bitcode module
loader functions.
Differential Revision: https://reviews.llvm.org/D140985
Since the linker does not resolve local symbols, we cannot look up
whether they are prevailing. The prior check was blocking all locals
from getting memprof summaries in the combined index.
Modified the existing test case to contain a local. This necessitated
some other fixes as the order of summary entries changed.
Differential Revision: https://reviews.llvm.org/D140786
Use deduction guides instead of helper functions.
The only non-automatic changes have been:
1. ArrayRef(some_uint8_pointer, 0) needs to be changed into ArrayRef(some_uint8_pointer, (size_t)0) to avoid an ambiguous call with ArrayRef((uint8_t*), (uint8_t*))
2. CVSymbol sym(makeArrayRef(symStorage)); needed to be rewritten as CVSymbol sym{ArrayRef(symStorage)}; otherwise the compiler is confused and thinks we have a (bad) function prototype. There was a few similar situation across the codebase.
3. ADL doesn't seem to work the same for deduction-guides and functions, so at some point the llvm namespace must be explicitly stated.
4. The "reference mode" of makeArrayRef(ArrayRef<T> &) that acts as no-op is not supported (a constructor cannot achieve that).
Per reviewers' comment, some useless makeArrayRef have been removed in the process.
This is a follow-up to https://reviews.llvm.org/D140896 that introduced
the deduction guides.
Differential Revision: https://reviews.llvm.org/D140955
