has been modular since r206822, and excluding it was leading to workarounds
such as the one in r219592, which this change removes.
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consider:
C1 = INT_MIN
C2 = -1
C1 * C2 overflows without a doubt but consider the following:
%x = i32 INT_MIN
This means that (%X /s C1) is 1 and (%X /s C1) /s C2 is -1.
N. B. Move the unsigned version of this transform to InstSimplify, it
doesn't create any new instructions.
This fixes PR21243.
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routines and fix all of the bugs they expose.
I hit a test case that crashed even without these asserts due to passing
a non-exiting latch to the ExitingBlock parameter of the trip count
computation machinery. However, when I add the nice asserts, it turns
out we have plenty of coverage of these bugs, they just didn't manifest
in crashers.
The core problem seems to stem from an assumption that the latch *is*
the exiting block. While this is often true, and somewhat the "normal"
way to think about loops, it isn't necessarily true. The correct way to
call the trip count routines in a *generic* fashion (that is, without
a particular exit in mind) is to just use the loop's single exiting
block if it has one. The trip count can't be computed generically unless
it does. This works great for the loop vectorizer. The loop unroller
actually *wants* to select the latch when it has to chose between
multiple exits because for unrolling it is the latch trips that matter.
But if this is the desire, it needs to explicitly guard for non-exiting
latches and check for the generic trip count in that case.
I've added the asserts, and added convenience APIs for querying the trip
count generically that check for a single exit block. I've kept the APIs
consistent between computing trip count and trip multiples.
Thansk to Mark for the help debugging and tracking down the *right* fix
here!
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It also makes it more aggressive in querying range information by
adding a call to isKnownPredicateWithRanges to
isLoopBackedgeGuardedByCond and isLoopEntryGuardedByCond.
phabricator: http://reviews.llvm.org/D5638
Reviewed by: atrick, hfinkel
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ScalarEvolution in the presence of multiple exits. Previously all
loops exits had to have identical counts for a loop trip count to be
considered computable. This pessimization was implemented by calling
getBackedgeTakenCount(L) rather than getExitCount(L, ExitingBlock)
inside of ScalarEvolution::getSmallConstantTripCount() (see the FIXME
in the comments of that function). The pessimization was added to fix
a corner case involving undefined behavior (pr/16130). This patch more
precisely handles the undefined behavior case allowing the pessimization
to be removed.
ControlsExit replaces IsSubExpr to more precisely track the case where
undefined behavior is expected to occur. Because undefined behavior is
tracked more precisely we can remove MustExit from ExitLimit. MustExit
was used to track the case where the limit was computed potentially
assuming undefined behavior even if undefined behavior didn't necessarily
occur.
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Some of r218231 was reverted with the code that used it in r218971, but not all
of it. This removes the rest (which is now dead).
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This reverts r218944, which reverted r218714, plus a bug fix.
Description of the bug in r218714 (by Nick)
The original patch forgot to check if the Scale in VariableGEPIndex flipped the
sign of the variable. The BasicAA pass iterates over the instructions in the
order they appear in the function, and so BasicAliasAnalysis::aliasGEP is
called with the variable it first comes across as parameter GEP1. Adding a
%reorder label puts the definition of %a after %b so aliasGEP is called with %b
as the first parameter and %a as the second. aliasGEP later calculates that %a
== %b + 1 - %idxprom where %idxprom >= 0 (if %a was passed as the first
parameter it would calculate %b == %a - 1 + %idxprom where %idxprom >= 0) -
ignoring that %idxprom is scaled by -1 here lead the patch to incorrectly
conclude that %a > %b.
Revised patch by Nick White, thanks! Thanks to Lang to isolating the bug.
Slightly modified by me to add an early exit from the loop and avoid
unnecessary, but expensive, function calls.
Original commit message:
Two related things:
1. Fixes a bug when calculating the offset in GetLinearExpression. The code
previously used zext to extend the offset, so negative offsets were converted
to large positive ones.
2. Enhance aliasGEP to deduce that, if the difference between two GEP
allocations is positive and all the variables that govern the offset are also
positive (i.e. the offset is strictly after the higher base pointer), then
locations that fit in the gap between the two base pointers are NoAlias.
Patch by Nick White!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219135 91177308-0d34-0410-b5e6-96231b3b80d8
This assertion is firing because -loop-unroll is failing to preserve
-loop-info (see PR20987). Improve it.
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We used to return PartialAlias if *either* variable being queried interacted
with arguments or globals. AFAICT, we can change this to only returning
MayAlias iff *both* variables being queried interacted with arguments or
globals.
Also, adding some basic functionality tests: some basic IPA tests, checking
that we give conservative responses with arguments/globals thrown in the mix,
and ensuring that we trace values through stores and loads.
Note that saying that 'x' interacted with arguments or globals means that the
Attributes of the StratifiedSet that 'x' belongs to has any bits set.
Patch by George Burgess IV, thanks!
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C++14 adds new builtin signatures for 'operator delete'. This change allows
new/delete pairs to be removed in C++14 onwards, as they were in C++11 and
before.
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This patch broke 447.dealII on Darwin. I'm currently working on a reduced
test-case, but reverting for now to keep the bots happy.
<rdar://problem/18530107>
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As discussed here:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20140609/220598.html
And again here:
http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-September/077168.html
The sqrt of a negative number when using the llvm intrinsic is undefined.
We should return undef rather than 0.0 to match the definition in the LLVM IR lang ref.
This change should not affect any code that isn't using "no-nans-fp-math";
ie, no-nans is a requirement for generating the llvm intrinsic in place of a sqrt function call.
Unfortunately, the behavior introduced by this patch will not match current gcc, xlc, icc, and
possibly other compilers. The current clang/llvm behavior of returning 0.0 doesn't either.
We knowingly approve of this difference with the other compilers in an attempt to flag code
that is invoking undefined behavior.
A front-end warning should also try to convince the user that the program will fail:
http://llvm.org/bugs/show_bug.cgi?id=21093
Differential Revision: http://reviews.llvm.org/D5527
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- Problem
One program takes ~3min to compile under -O2. This happens after a certain
function A is inlined ~700 times in a function B, inserting thousands of new
BBs. This leads to 80% of the compilation time spent in
GVN::processNonLocalLoad and
MemoryDependenceAnalysis::getNonLocalPointerDependency, while searching for
nonlocal information for basic blocks.
Usually, to avoid spending a long time to process nonlocal loads, GVN bails out
if it gets more than 100 deps as a result from
MD->getNonLocalPointerDependency. However this only happens *after* all
nonlocal information for BBs have been computed, which is the bottleneck in
this scenario. For instance, there are 8280 times where
getNonLocalPointerDependency returns deps with more than 100 bbs and from
those, 600 times it returns more than 1000 blocks.
- Solution
Bail out early during the nonlocal info computation whenever we reach a
specified threshold. This patch proposes a 100 BBs threshold, it also
reduces the compile time from 3min to 23s.
- Testing
The test-suite presented no compile nor execution time regressions.
Some numbers from my machine (x86_64 darwin):
- 17s under -Oz (which avoids inlining).
- 1.3s under -O1.
- 2m51s under -O2 ToT
*** 23s under -O2 w/ Result.size() > 100
- 1m54s under -O2 w/ Result.size() > 500
With NumResultsLimit = 100, GVN yields the same outcome as in the
unlimited 3min version.
http://reviews.llvm.org/D5532
rdar://problem/18188041
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Two related things:
1. Fixes a bug when calculating the offset in GetLinearExpression. The code
previously used zext to extend the offset, so negative offsets were converted
to large positive ones.
2. Enhance aliasGEP to deduce that, if the difference between two GEP
allocations is positive and all the variables that govern the offset are also
positive (i.e. the offset is strictly after the higher base pointer), then
locations that fit in the gap between the two base pointers are NoAlias.
Patch by Nick White!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218714 91177308-0d34-0410-b5e6-96231b3b80d8
The annotation instructions are dropped during codegen and have no
impact on size. In some cases, the annotations were preventing the
unroller from unrolling a loop because the annotation calls were
pushing the cost over the unrolling threshold.
Differential Revision: http://reviews.llvm.org/D5335
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The doFinalization method checks that the LoopToAliasSetMap is
empty. LICM populates that map as it runs through the loop nest,
deleting the entries for child loops as it goes. However, if a child
loop is deleted by another pass (e.g. unrolling) then the loop will
never be deleted from the map because LICM walks the loop nest to
find entries it can delete.
The fix is to delete the loop from the map and free the alias set
when the loop is deleted from the loop nest.
Differential Revision: http://reviews.llvm.org/D5305
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for LVI algorithm. For a specific value to be lowered, when the number of basic
blocks being checked for overdefined lattice value is larger than
lvi-overdefined-BB-threshold, or the times of encountering overdefined value
for a single basic block is larger than lvi-overdefined-threshold, the LVI
algorithm will stop further lowering the lattice value.
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shim between the TargetTransformInfo immutable pass and the Subtarget
via the TargetMachine and Function. Migrate a single call from
BasicTargetTransformInfo as an example and provide shims where TargetMachine
begins taking a Function to determine the subtarget.
No functional change.
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Some ICmpInsts when anded/ored with another ICmpInst trivially reduces
to true or false depending on whether or not all integers or no integers
satisfy the intersected/unioned range.
This sort of trivial looking code can come about when InstCombine
performs a range reduction-type operation on sdiv and the like.
This fixes PR20916.
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This adds a basic (but important) use of @llvm.assume calls in ScalarEvolution.
When SE is attempting to validate a condition guarding a loop (such as whether
or not the loop count can be zero), this check should also include dominating
assumptions.
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This change teaches LazyValueInfo to use the @llvm.assume intrinsic. Like with
the known-bits change (r217342), this requires feeding a "context" instruction
pointer through many functions. Aside from a little refactoring to reuse the
logic that turns predicates into constant ranges in LVI, the only new code is
that which can 'merge' the range from an assumption into that otherwise
computed. There is also a small addition to JumpThreading so that it can have
LVI use assumptions in the same block as the comparison feeding a conditional
branch.
With this patch, we can now simplify this as expected:
int foo(int a) {
__builtin_assume(a > 5);
if (a > 3) {
bar();
return 1;
}
return 0;
}
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This builds on r217342, which added the infrastructure to compute known bits
using assumptions (@llvm.assume calls). That original commit added only a few
patterns (to catch common cases related to determining pointer alignment); this
change adds several other patterns for simple cases.
r217342 contained that, for assume(v & b = a), bits in the mask
that are known to be one, we can propagate known bits from the a to v. It also
had a known-bits transfer for assume(a = b). This patch adds:
assume(~(v & b) = a) : For those bits in the mask that are known to be one, we
can propagate inverted known bits from the a to v.
assume(v | b = a) : For those bits in b that are known to be zero, we can
propagate known bits from the a to v.
assume(~(v | b) = a): For those bits in b that are known to be zero, we can
propagate inverted known bits from the a to v.
assume(v ^ b = a) : For those bits in b that are known to be zero, we can
propagate known bits from the a to v. For those bits in
b that are known to be one, we can propagate inverted
known bits from the a to v.
assume(~(v ^ b) = a) : For those bits in b that are known to be zero, we can
propagate inverted known bits from the a to v. For those
bits in b that are known to be one, we can propagate
known bits from the a to v.
assume(v << c = a) : For those bits in a that are known, we can propagate them
to known bits in v shifted to the right by c.
assume(~(v << c) = a) : For those bits in a that are known, we can propagate
them inverted to known bits in v shifted to the right by c.
assume(v >> c = a) : For those bits in a that are known, we can propagate them
to known bits in v shifted to the right by c.
assume(~(v >> c) = a) : For those bits in a that are known, we can propagate
them inverted to known bits in v shifted to the right by c.
assume(v >=_s c) where c is non-negative: The sign bit of v is zero
assume(v >_s c) where c is at least -1: The sign bit of v is zero
assume(v <=_s c) where c is negative: The sign bit of v is one
assume(v <_s c) where c is non-positive: The sign bit of v is one
assume(v <=_u c): Transfer the known high zero bits
assume(v <_u c): Transfer the known high zero bits (if c is know to be a power
of 2, transfer one more)
A small addition to InstCombine was necessary for some of the test cases. The
problem is that when InstCombine was simplifying and, or, etc. it would fail to
check the 'do I know all of the bits' condition before checking less specific
conditions and would not fully constant-fold the result. I'm not sure how to
trigger this aside from using assumptions, so I've just included the change
here.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217343 91177308-0d34-0410-b5e6-96231b3b80d8
This change, which allows @llvm.assume to be used from within computeKnownBits
(and other associated functions in ValueTracking), adds some (optional)
parameters to computeKnownBits and friends. These functions now (optionally)
take a "context" instruction pointer, an AssumptionTracker pointer, and also a
DomTree pointer, and most of the changes are just to pass this new information
when it is easily available from InstSimplify, InstCombine, etc.
As explained below, the significant conceptual change is that known properties
of a value might depend on the control-flow location of the use (because we
care that the @llvm.assume dominates the use because assumptions have
control-flow dependencies). This means that, when we ask if bits are known in a
value, we might get different answers for different uses.
The significant changes are all in ValueTracking. Two main changes: First, as
with the rest of the code, new parameters need to be passed around. To make
this easier, I grouped them into a structure, and I made internal static
versions of the relevant functions that take this structure as a parameter. The
new code does as you might expect, it looks for @llvm.assume calls that make
use of the value we're trying to learn something about (often indirectly),
attempts to pattern match that expression, and uses the result if successful.
By making use of the AssumptionTracker, the process of finding @llvm.assume
calls is not expensive.
Part of the structure being passed around inside ValueTracking is a set of
already-considered @llvm.assume calls. This is to prevent a query using, for
example, the assume(a == b), to recurse on itself. The context and DT params
are used to find applicable assumptions. An assumption needs to dominate the
context instruction, or come after it deterministically. In this latter case we
only handle the specific case where both the assumption and the context
instruction are in the same block, and we need to exclude assumptions from
being used to simplify their own ephemeral values (those which contribute only
to the assumption) because otherwise the assumption would prove its feeding
comparison trivial and would be removed.
This commit adds the plumbing and the logic for a simple masked-bit propagation
(just enough to write a regression test). Future commits add more patterns
(and, correspondingly, more regression tests).
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This adds a set of utility functions for collecting 'ephemeral' values. These
are LLVM IR values that are used only by @llvm.assume intrinsics (directly or
indirectly), and thus will be removed prior to code generation, implying that
they should be considered free for certain purposes (like inlining). The
inliner's cost analysis, and a few other passes, have been updated to account
for ephemeral values using the provided functionality.
This functionality is important for the usability of @llvm.assume, because it
limits the "non-local" side-effects of adding llvm.assume on inlining, loop
unrolling, etc. (these are hints, and do not generate code, so they should not
directly contribute to estimates of execution cost).
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This adds an immutable pass, AssumptionTracker, which keeps a cache of
@llvm.assume call instructions within a module. It uses callback value handles
to keep stale functions and intrinsics out of the map, and it relies on any
code that creates new @llvm.assume calls to notify it of the new instructions.
The benefit is that code needing to find @llvm.assume intrinsics can do so
directly, without scanning the function, thus allowing the cost of @llvm.assume
handling to be negligible when none are present.
The current design is intended to be lightweight. We don't keep track of
anything until we need a list of assumptions in some function. The first time
this happens, we scan the function. After that, we add/remove @llvm.assume
calls from the cache in response to registration calls and ValueHandle
callbacks.
There are no new direct test cases for this pass, but because it calls it
validation function upon module finalization, we'll pick up detectable
inconsistencies from the other tests that touch @llvm.assume calls.
This pass will be used by follow-up commits that make use of @llvm.assume.
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Fixes this (the warning is right, the unsigned value is not negative):
lib/Analysis/StratifiedSets.h:689:53: warning: comparison of unsigned expression >= 0 is always true [-Wtautological-compare]
bool inbounds(StratifiedIndex N) const { return N >= 0 && N < Links.size(); }
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This provides an implementation of CFL alias analysis (including some
supporting data structures). Currently, we don't have any extremely fancy
features, sans some interprocedural analysis (i.e. no field sensitivity, etc.),
and we do best sitting behind BasicAA + TBAA. In such a configuration, we take
~0.6-0.8% of total compile time, and give ~7-8% NoAlias responses to queries
TBAA and BasicAA couldn't answer when bootstrapping LLVM. In testing this on
other projects, we've seen up to 10.5% of queries dropped by BasicAA+TBAA
answered with NoAlias by this algorithm.
Patch by George Burgess IV (with minor modifications by me -- mostly adapting
some BasicAA tests), thanks!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216970 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
MemoryDependenceAnalysis is currently cautious when the QueryInstr is an atomic
load or store, but I forgot to check for atomic cmpxchg/atomicrmw. This patch
is a way of fixing that, and making it less brittle (i.e. no risk that I forget
another possible kind of atomic, even if the IR ends up changing in the future),
by adding a fallback checking mayReadOrWriteFromMemory.
Thanks to Philip Reames for finding this bug and suggesting this solution in
http://reviews.llvm.org/D4845
Sadly, I don't see how to add a test for this, since the passes depending on
MemoryDependenceAnalysis won't trigger for an atomic rmw anyway. Does anyone
see a way for testing it?
Test Plan: none possible at first sight
Reviewers: jfb, reames
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D5019
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