Summary:
Backends can use setInsertFencesForAtomic to signal to the middle-end that
montonic is the only memory ordering they can accept for
stores/loads/rmws/cmpxchg. The code lowering those accesses with a stronger
ordering to fences + monotonic accesses is currently living in
SelectionDAGBuilder.cpp. In this patch I propose moving this logic out of it
for several reasons:
- There is lots of redundancy to avoid: extremely similar logic already
exists in AtomicExpand.
- The current code in SelectionDAGBuilder does not use any target-hooks, it
does the same transformation for every backend that requires it
- As a result it is plain *unsound*, as it was apparently designed for ARM.
It happens to mostly work for the other targets because they are extremely
conservative, but Power for example had to switch to AtomicExpand to be
able to use lwsync safely (see r218331).
- Because it produces IR-level fences, it cannot be made sound ! This is noted
in the C++11 standard (section 29.3, page 1140):
```
Fences cannot, in general, be used to restore sequential consistency for atomic
operations with weaker ordering semantics.
```
It can also be seen by the following example (called IRIW in the litterature):
```
atomic<int> x = y = 0;
int r1, r2, r3, r4;
Thread 0:
x.store(1);
Thread 1:
y.store(1);
Thread 2:
r1 = x.load();
r2 = y.load();
Thread 3:
r3 = y.load();
r4 = x.load();
```
r1 = r3 = 1 and r2 = r4 = 0 is impossible as long as the accesses are all seq_cst.
But if they are lowered to monotonic accesses, no amount of fences can prevent it..
This patch does three things (I could cut it into parts, but then some of them
would not be tested/testable, please tell me if you would prefer that):
- it provides a default implementation for emitLeadingFence/emitTrailingFence in
terms of IR-level fences, that mimic the original logic of SelectionDAGBuilder.
As we saw above, this is unsound, but the best that can be done without knowing
the targets well (and there is a comment warning about this risk).
- it then switches Mips/Sparc/XCore to use AtomicExpand, relying on this default
implementation (that exactly replicates the logic of SelectionDAGBuilder, so no
functional change)
- it finally erase this logic from SelectionDAGBuilder as it is dead-code.
Ideally, each target would define its own override for emitLeading/TrailingFence
using target-specific fences, but I do not know the Sparc/Mips/XCore memory model
well enough to do this, and they appear to be dealing fine with the ARM-inspired
default expansion for now (probably because they are overly conservative, as
Power was). If anyone wants to compile fences more agressively on these
platforms, the long comment should make it clear why he should first override
emitLeading/TrailingFence.
Test Plan: make check-all, no functional change
Reviewers: jfb, t.p.northover
Subscribers: aemerson, llvm-commits
Differential Revision: http://reviews.llvm.org/D5474
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219957 91177308-0d34-0410-b5e6-96231b3b80d8
map, this makes sure that we can compile the same code for two different
ABIs (hard and soft float) in the same module.
Update one testcase accordingly (and fix some confusing naming) and
add a new testcase as well with the ordering swapped which would
highlight the problem.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218632 91177308-0d34-0410-b5e6-96231b3b80d8
based on the Function. This is currently used to implement
mips16 support in the mips backend via the existing module
pass resetting the subtarget.
Things to note:
a) This involved running resetTargetOptions before creating a
new subtarget so that code generation options like soft-float
could be recognized when creating the new subtarget. This is
to deal with initialization code in isel lowering that only
paid attention to the initial value.
b) Many of the existing testcases weren't using the soft-float
feature correctly. I've corrected these based on the check
values assuming that was the desired behavior.
c) The mips port now pays attention to the target-cpu and
target-features strings when generating code for a particular
function. I've removed these from one function where the
requested cpu and features didn't match the check lines in
the testcase.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218492 91177308-0d34-0410-b5e6-96231b3b80d8
Approved by Jim Grosbach, Lang Hames, Rafael Espindola.
This reinstates commits r215111, 215115, 215116, 215117, 215136.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216982 91177308-0d34-0410-b5e6-96231b3b80d8
be deleted. This will be reapplied as soon as possible and before
the 3.6 branch date at any rate.
Approved by Jim Grosbach, Lang Hames, Rafael Espindola.
This reverts commits r215111, 215115, 215116, 215117, 215136.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215154 91177308-0d34-0410-b5e6-96231b3b80d8
I am sure we will be finding bits and pieces of dead code for years to
come, but this is a good start.
Thanks to Lang Hames for making MCJIT a good replacement!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215111 91177308-0d34-0410-b5e6-96231b3b80d8
shorter/easier and have the DAG use that to do the same lookup. This
can be used in the future for TargetMachine based caching lookups from
the MachineFunction easily.
Update the MIPS subtarget switching machinery to update this pointer
at the same time it runs.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214838 91177308-0d34-0410-b5e6-96231b3b80d8
This pass attempts to speculatively use a sqrt instruction if one exists on the target, falling back to a libcall if the target instruction returned NaN.
This was enabled for MIPS and System-Z, but is well guarded and is good for most targets - GCC does this for (that I've checked) X86, ARM and AArch64.
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a) Move the replacement level decision to the target machine.
b) Create additional subtargets at the TargetMachine level to
cache and make replacement easy.
c) Make the mips16 features obvious.
d) Remove the override logic as it no longer does anything.
e) Have MipsModuleDAGToDAGISel take only the target machine.
f) Have the constant islands pass grab the current subtarget
from the MachineFunction (via the TargetMachine) instead
of caching it.
g) Unconditionally initialize TLOF.
h) Remove the old complicated subtarget based resetting and
replace it with simple conditionals.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213430 91177308-0d34-0410-b5e6-96231b3b80d8
two reasons:
a) we're already caching the target machine which contains it,
b) which relocation model you get is dependent upon whether or
not you ask before MCCodeGenInfo is constructed on the target
machine, so avoid any latent issues there.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213420 91177308-0d34-0410-b5e6-96231b3b80d8
behavior based on other files defining DEBUG_TYPE, which means it cannot
define DEBUG_TYPE at all. This is actually better IMO as it forces folks
to define relevant DEBUG_TYPEs for their files. However, it requires all
files that currently use DEBUG(...) to define a DEBUG_TYPE if they don't
already. I've updated all such files in LLVM and will do the same for
other upstream projects.
This still leaves one important change in how LLVM uses the DEBUG_TYPE
macro going forward: we need to only define the macro *after* header
files have been #include-ed. Previously, this wasn't possible because
Debug.h required the macro to be pre-defined. This commit removes that.
By defining DEBUG_TYPE after the includes two things are fixed:
- Header files that need to provide a DEBUG_TYPE for some inline code
can do so by defining the macro before their inline code and undef-ing
it afterward so the macro does not escape.
- We no longer have rampant ODR violations due to including headers with
different DEBUG_TYPE definitions. This may be mostly an academic
violation today, but with modules these types of violations are easy
to check for and potentially very relevant.
Where necessary to suppor headers with DEBUG_TYPE, I have moved the
definitions below the includes in this commit. I plan to move the rest
of the DEBUG_TYPE macros in LLVM in subsequent commits; this one is big
enough.
The comments in Debug.h, which were hilariously out of date already,
have been updated to reflect the recommended practice going forward.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206822 91177308-0d34-0410-b5e6-96231b3b80d8
subsequent changes are easier to review. About to fix some layering
issues, and wanted to separate out the necessary churn.
Also comment and sink the include of "Windows.h" in three .inc files to
match the usage in Memory.inc.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198685 91177308-0d34-0410-b5e6-96231b3b80d8
Before this patch any program that wanted to know the final symbol name of a
GlobalValue had to link with Target.
This patch implements a compromise solution where the mangler uses DataLayout.
This way, any tool that already links with Target (llc, clang) gets the exact
behavior as before and new IR files can be mangled without linking with Target.
With this patch the mangler is constructed with just a DataLayout and DataLayout
is extended to include the information the Mangler needs.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198438 91177308-0d34-0410-b5e6-96231b3b80d8
Robin Morisset
Eric Christopher
David Majnemer
Rafael Espindola
James Molloy
Craig Topper
Chandler Carruth
Reed Kotler