This is the last JumpThreading patch for getting the performance numbers shown at
https://reviews.llvm.org/D84940#2184653 .
This patch makes ProcessBlock call ProcessBranchOnPHI when the branch condition
is freeze(phi) as well (originally it calls the function when the condition is
phi only).
Since what ProcessBranchOnPHI does is to duplicate the basic block into
predecessors if profitable, it is still valid when the condition is freeze(phi)
too.
```
p = phi [a, pred1] [b, pred2]
p.fr = freeze p
br p.fr, ...
=>
pred1:
p.fr = freeze a
br p.fr, ...
pred2:
p.fr2 = freeze b
br p.fr2, ...
```
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D85029
This is a simple patch that makes freeze as a zero-cost instruction, as bitcast already is.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D85023
As discussed in D84949, this removes the constraint to cast since it does not
cause compile time degradation.
Reviewed By: lebedev.ri
Differential Revision: https://reviews.llvm.org/D85188
Compared to the optimized code with branch conditions never frozen,
limiting the type of freeze's operand causes generation of suboptimal code in
some cases.
I would like to suggest removing the constraint, as this patch does.
If the number of freeze instructions becomes significant, this can be revisited.
Differential Revision: https://reviews.llvm.org/D84949
This patch allows SimplifyPartiallyRedundantLoad work when
the branch condition was frozen.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D84944
This patch makes JumpThreading fold br(freeze(undef)) if the freeze instruction
is only used by the branch.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D84818
This patch adds a basic support for freeze instruction to JumpThreading
by making ComputeValueKnownInPredecessorsImpl look into its operand.
Reviewed By: efriedma, nikic
Differential Revision: https://reviews.llvm.org/D84598
SplitBlockPredecessors() can not split blocks that have such terminators,
and in two other places we already ensure that we don't end up calling
SplitBlockPredecessors() on such blocks. Do so in one more place.
Fixes https://bugs.llvm.org/show_bug.cgi?id=46857
Summary:
This patch simplifies FindMostPopularDest without changing the
functionality.
Given a list of jump threading destinations, the function finds the
most popular destination. To ensure determinism when there are
multiple destinations with the highest popularity, the function picks
the first one in the successor list with the highest popularity.
Without this patch:
- The function populates DestPopularity -- a histogram mapping
destinations to their respective occurrence counts.
- Then we iterate over DestPopularity, looking for the highest
popularity while building a vector of destinations with the highest
popularity.
- Finally, we iterate the successor list, looking for the destination
with the highest popularity.
With this patch:
- We implement DestPopularity with MapVector instead of DenseMap. We
populate the map with popularity 0 for all successors in the order
they appear in the successor list.
- We build the histogram in the same way as before.
- We simply use std::max_element on DestPopularity to find the most
popular destination. The use of MapVector ensures determinism.
Reviewers: wmi, efriedma
Reviewed By: wmi
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D81030
Hide the method that allows setting probability for particular edge
and introduce a public method that sets probabilities for all
outgoing edges at once.
Setting individual edge probability is error prone. More over it is
difficult to check that the total probability is 1.0 because there is
no easy way to know when the user finished setting all
the probabilities.
Related bug is fixed in BranchProbabilityInfo::calcMetadataWeights().
Changing unreachable branch probabilities to raw(1) and distributing
the rest (oldProbability - raw(1)) over the reachable branches could
introduce total probability inaccuracy bigger than 1/numOfBranches.
Reviewers: yamauchi, ebrevnov
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D79396
After D76797 the dominator tree is no longer used in LVI, so we
can remove it as a pass dependency, and also get rid of the
dominator tree enabling/disabling logic in JumpThreading.
Apart from cleaning up the code, this also clarifies LVI
cache consistency, in that the LVI cache can no longer
depend on whether the DT was or wasn't enabled due to
pending DT updates at any given time.
Differential Revision: https://reviews.llvm.org/D76985
Hide the method that allows setting probability for particular
edge and introduce a public method that sets probabilities for
all outgoing edges at once.
Setting individual edge probability is error prone. More over
it is difficult to check that the total probability is 1.0
because there is no easy way to know when the user finished
setting all the probabilities.
Reviewers: yamauchi, ebrevnov
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D79396
Summary:
ComputeValueKnownInPredecessorsImpl is the main folding mechanism in
JumpThreading.cpp. To avoid potential infinite recursion while
chasing use-def chains, it uses:
DenseSet<std::pair<Value *, BasicBlock *>> &RecursionSet
to keep track of Value-BB pairs that we've processed.
Now, when ComputeValueKnownInPredecessorsImpl recursively calls
itself, it always passes BB as is, so the second element is always BB.
This patch simplifes the function by dropping "BasicBlock *" from
RecursionSet.
Reviewers: wmi, efriedma
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D77699
Summary:
Select folding in JumpThreading can create a conditional branch on a
code patch that did not have one in the original program. This is not a
valid transformation in sanitize_memory functions.
Note that JumpThreading does select folding in 3 different places. Two
of them seem safe - they apply to a select instruction in a BB that ends
with an unconditional branch to another BB, which (in turn) ends with a
conditional branch or a switch with the same condition.
Fixes PR45220.
Reviewers: glider, dvyukov, efriedma
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D76332
Summary:
This patch fixes https://bugs.llvm.org/show_bug.cgi?id=44611 by
preventing an infinite loop in the jump threading pass when
-jump-threading-across-loop-headers is on. Specifically, without this
patch, jump threading through two basic blocks would trigger on the
same area of the CFG over and over, resulting in an infinite loop.
Consider testcase PR44611-across-header-hang.ll in this patch. The
first opportunity to thread through two basic blocks is:
from bb_body2 through bb_header and bb_body1 to bb_body2.
The pass duplicates bb_header and bb_body1 as, say, bb_header.thread1
and bb_body1.thread1. Since bb_header contains a successor edge back
to itself, bb_header.thread1 also contains a successor edge to
bb_header, immediately giving rise to the next jump threading
opportunity:
from bb_header.thread1 through bb_header and bb_body1 to bb_body2.
After that, we repeatedly thread an incoming edge into bb_header
through bb_header and bb_body1 to bb_body2. In other words, we keep
peeling one iteration from bb_header's self loop.
The patch fixes the problem by preventing the pass from duplicating a
basic block containing a self loop.
Reviewers: wmi, junparser, efriedma
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D76390
Fixes https://bugs.llvm.org/show_bug.cgi?id=44922 (caused by 4698bf145d)
ThreadThroughTwoBasicBlocks assumes PredBBBranch is conditional. The following code can segfault.
AddPHINodeEntriesForMappedBlock(PredBBBranch->getSuccessor(1), PredBB, NewBB,
ValueMapping);
We can also allow unconditional PredBB, but the produced code is not
better.
Reviewed By: kazu
Differential Revision: https://reviews.llvm.org/D74747
This patch is a fix following the revert of 72ce759
(https://reviews.llvm.org/rG72ce759928e6dfee6a9efa310b966c19722352ba)
and fixes the failure that it caused.
The above patch failed on the Thread Sanitizer buildbot with an out of
memory error. After an investigation, the cause was identified as an
explosion in debug intrinsics while running the Jump Threading pass on
ModuleMap.ll. The above patched prevented debug intrinsics from being
dropped when their Basic Block was deleted due to being "empty". In this
case, one of the functions in ModuleMap.ll had (after many optimization
passes) a very large number of debug intrinsics representing a set of
repeatedly inlined variables. Previously the vast majority of these were
silently dropped during Jump Threading when their blocks were deleted,
but as of the above patch they survived for longer, causing a large
increase in the number of debug intrinsics. These intrinsics were then
repeatedly cloned by the Jump Threading pass as edges were threaded,
multiplying the intrinsic count further. The memory consumed by this
process spiralled out of control, crashing the buildbot that uses TSan
(which has an estimated 5-10x memory overhead compared to non-sanitized
builds).
This patch adds RemoveRedundantDbgInstrs to the Jump Threading pass, in
order to reduce the number of debug intrinsics down to a manageable
amount in cases where many intrinsics for the same variable end up
bunched together contiguously, as in this case.
Differential Revision: https://reviews.llvm.org/D73054
This reverts commit 41784bed01.
Since the original revision ead815924e,
this revision fixes three issues:
- This revision fixes the Windows build. My original patch improperly
copied EH pads on Windows. This patch disregards jump threading
opportunities having to do with EH pads.
- This revision fixes jump threading to a wrong destination.
Specifically, my original patch treated any Constant other than 0 as 1
while evaluating the branch condition. This bug led to treating
constant expressions like:
icmp ugt i8* null, inttoptr (i64 4 to i8*)
to "true". This patch fixes the bug by calling isOneValue.
- This revision fixes the cost calculation of two basic blocks being
threaded through. Note that getJumpThreadDuplicationCost returns
"(unsigned)~0" for those basic blocks that cannot be duplicated. If
we sum of two return values from getJumpThreadDuplicationCost, we
could have an unsigned overflow like:
(unsigned)~0 + 5 = 4
and mistakenly determine that it's safe and profitable to proceed
with the jump threading opportunity. The patch fixes the bug by
checking each return value before summing them up.
[JumpThreading] Thread jumps through two basic blocks
Summary:
This patch teaches JumpThreading.cpp to thread through two basic
blocks like:
bb3:
%var = phi i32* [ null, %bb1 ], [ @a, %bb2 ]
%tobool = icmp eq i32 %cond, 0
br i1 %tobool, label %bb4, label ...
bb4:
%cmp = icmp eq i32* %var, null
br i1 %cmp, label bb5, label bb6
by duplicating basic blocks like bb3 above. Once we duplicate bb3 as
bb3.dup and redirect edge bb2->bb3 to bb2->bb3.dup, we have:
bb3:
%var = phi i32* [ @a, %bb2 ]
%tobool = icmp eq i32 %cond, 0
br i1 %tobool, label %bb4, label ...
bb3.dup:
%var = phi i32* [ null, %bb1 ]
%tobool = icmp eq i32 %cond, 0
br i1 %tobool, label %bb4, label ...
bb4:
%cmp = icmp eq i32* %var, null
br i1 %cmp, label bb5, label bb6
Then the existing code in JumpThreading.cpp can thread edge
bb3.dup->bb4 through bb4 and eventually create bb3.dup->bb5.
Reviewers: wmi
Subscribers: hiraditya, jfb, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70247
Duplicating instructions can lead to code size increases but using
a threshold of 3 is good for reducing code size.
Differential Revision: https://reviews.llvm.org/D72916
Summary:
With this patch, we no longer cache F.hasProfileData(). We simply
call the function again.
I'm doing this because:
- JumpThreadingPass also has a member variable named HasProfileData,
which is very confusing,
- the function is very lightweight, and
- this patch makes JumpThreading::runOnFunction more consistent with
JumpThreadingPass::run.
Subscribers: hiraditya, jfb, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70602
Summary:
Without this patch, the jump threading pass ignores profiling data
whenever we invoke the pass with the new pass manager.
Specifically, JumpThreadingPass::run calls runImpl with class variable
HasProfileData always set to false. In turn, runImpl sets
HasProfileData to false again:
HasProfileData = HasProfileData_;
In the end, we don't use profiling data at all with the new pass
manager.
This patch fixes the problem by passing F.hasProfileData() to runImpl.
The bug appears to have been introduced at:
https://reviews.llvm.org/D41461
which removed local variable HasProfileData in JumpThreadingPass::run
even though there was one more use left in the same function. As a
result, the remaining use ended referring to the class variable
instead.
Note that F.hasProfileData is an extremely lightweight function, so I
don't see the need to cache its result. Once this patch is approved,
I'm planning to stop caching the result of F.hasProfileData in
runOnFunction.
Reviewers: wmi, eli.friedman
Subscribers: hiraditya, jfb, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70509
Summary:
This patch moves various checks from ThreadEdge to new function
TryThreadEdge The rational behind this is that I'd like to use
ThreadEdge without its checks in my upcoming patch.
This patch preserves lightweight checks as assertions in ThreadEdge.
ThreadEdge does not repeat the cost check, however.
Reviewers: wmi
Subscribers: hiraditya, jfb, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70338
This file lists every pass in LLVM, and is included by Pass.h, which is
very popular. Every time we add, remove, or rename a pass in LLVM, it
caused lots of recompilation.
I found this fact by looking at this table, which is sorted by the
number of times a file was changed over the last 100,000 git commits
multiplied by the number of object files that depend on it in the
current checkout:
recompiles touches affected_files header
342380 95 3604 llvm/include/llvm/ADT/STLExtras.h
314730 234 1345 llvm/include/llvm/InitializePasses.h
307036 118 2602 llvm/include/llvm/ADT/APInt.h
213049 59 3611 llvm/include/llvm/Support/MathExtras.h
170422 47 3626 llvm/include/llvm/Support/Compiler.h
162225 45 3605 llvm/include/llvm/ADT/Optional.h
158319 63 2513 llvm/include/llvm/ADT/Triple.h
140322 39 3598 llvm/include/llvm/ADT/StringRef.h
137647 59 2333 llvm/include/llvm/Support/Error.h
131619 73 1803 llvm/include/llvm/Support/FileSystem.h
Before this change, touching InitializePasses.h would cause 1345 files
to recompile. After this change, touching it only causes 550 compiles in
an incremental rebuild.
Reviewers: bkramer, asbirlea, bollu, jdoerfert
Differential Revision: https://reviews.llvm.org/D70211
Summary:
This patch factors out code to clone instructions -- partly for
readability and partly to facilitate an upcoming patch of my own.
Reviewers: wmi
Subscribers: hiraditya, jfb, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69861
Summary:
This patch factors out code to merge a basic block with its sole
successor -- partly for readability and partly to facilitate an
upcoming patch of my own.
Reviewers: wmi
Subscribers: hiraditya, jfb, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69852
Summary:
This patch factors out common code to update the SSA form in
JumpThreading.cpp -- partly for readability and partly to facilitate
an coming patch of my own.
Reviewers: wmi
Subscribers: hiraditya, jfb, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69811
The static analyzer is warning about a potential null dereference, but we should be able to use cast<> directly and if not assert will fire for us.
llvm-svn: 375103
Summary:
This is the first change to enable the TLI to be built per-function so
that -fno-builtin* handling can be migrated to use function attributes.
See discussion on D61634 for background. This is an enabler for fixing
handling of these options for LTO, for example.
This change should not affect behavior, as the provided function is not
yet used to build a specifically per-function TLI, but rather enables
that migration.
Most of the changes were very mechanical, e.g. passing a Function to the
legacy analysis pass's getTLI interface, or in Module level cases,
adding a callback. This is similar to the way the per-function TTI
analysis works.
There was one place where we were looking for builtins but not in the
context of a specific function. See FindCXAAtExit in
lib/Transforms/IPO/GlobalOpt.cpp. I'm somewhat concerned my workaround
could provide the wrong behavior in some corner cases. Suggestions
welcome.
Reviewers: chandlerc, hfinkel
Subscribers: arsenm, dschuff, jvesely, nhaehnle, mehdi_amini, javed.absar, sbc100, jgravelle-google, eraman, aheejin, steven_wu, george.burgess.iv, dexonsmith, jfb, asbirlea, gchatelet, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66428
llvm-svn: 371284
unreachable loop.
updatePredecessorProfileMetadata in jumpthreading tries to find the
first dominating predecessor block for a PHI value by searching upwards
the predecessor block chain.
But jumpthreading may see some temporary IR state which contains
unreachable bb not being cleaned up. If an unreachable loop happens to
be on the predecessor block chain, keeping chasing the predecessor
block will run into an infinite loop.
The patch fixes it.
Differential Revision: https://reviews.llvm.org/D65310
llvm-svn: 367154
If the block being cloned contains a PHI node, in general, we need to
clone that PHI node, even though it's trivial. If the operand of the PHI
is an instruction in the block being cloned, the correct value for the
operand doesn't exist until SSAUpdater constructs it.
We usually don't hit this issue because we try to avoid threading across
loop headers, but it's possible to hit this in some cases involving
irreducible CFGs. I added a flag to allow threading across loop headers
to make the testcase easier to understand.
Thanks to Brian Rzycki for reducing the testcase.
Fixes https://bugs.llvm.org/show_bug.cgi?id=42085.
Differential Revision: https://reviews.llvm.org/D63913
llvm-svn: 365094
Summary:
The return value of a TryToUnfoldSelect call was not checked, which led to an
incorrectly preserved loop info and some crash.
The original crash was reported on https://reviews.llvm.org/D59514.
Reviewers: davidxl, amehsan
Reviewed By: davidxl
Subscribers: fhahn, brzycki, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D61920
llvm-svn: 360780
Fixes bug 40992: https://bugs.llvm.org/show_bug.cgi?id=40992
There is potential for miscompiled code emitted from JumpThreading when
analyzing a block with one or more indirectbr or callbr predecessors. The
ProcessThreadableEdges() function incorrectly folds conditional branches
into an unconditional branch.
This patch prevents incorrect branch folding without fully pessimizing
other potential threading opportunities through the same basic block.
This IR shape was manually fed in via opt and is unclear if clang and the
full pass pipeline will ever emit similar code shapes.
Thanks to Matthias Liedtke for the bug report and simplified IR example.
Differential Revision: https://reviews.llvm.org/D60284
llvm-svn: 357930
Fixes bug 37966: https://bugs.llvm.org/show_bug.cgi?id=37966
The Jump Threading pass will replace certain conditional branch
instructions with unconditional branches when it can prove that only one
branch can occur. Prior to this patch, it would not carry the debug
info from the old instruction to the new one.
This patch fixes the bug described by copying the debug info from the
conditional branch instruction to the new unconditional branch
instruction, and adds a regression test for the Jump Threading pass that
covers this case.
Patch by Stephen Tozer!
Differential Revision: https://reviews.llvm.org/D58963
llvm-svn: 355822
Summary:
This patch separates two semantics of `applyUpdates`:
1. User provides an accurate CFG diff and the dominator tree is updated according to the difference of `the number of edge insertions` and `the number of edge deletions` to infer the status of an edge before and after the update.
2. User provides a sequence of hints. Updates mentioned in this sequence might never happened and even duplicated.
Logic changes:
Previously, removing invalid updates is considered a side-effect of deduplication and is not guaranteed to be reliable. To handle the second semantic, `applyUpdates` does validity checking before deduplication, which can cause updates that have already been applied to be submitted again. Then, different calls to `applyUpdates` might cause unintended consequences, for example,
```
DTU(Lazy) and Edge A->B exists.
1. DTU.applyUpdates({{Delete, A, B}, {Insert, A, B}}) // User expects these 2 updates result in a no-op, but {Insert, A, B} is queued
2. Remove A->B
3. DTU.applyUpdates({{Delete, A, B}}) // DTU cancels this update with {Insert, A, B} mentioned above together (Unintended)
```
But by restricting the precondition that updates of an edge need to be strictly ordered as how CFG changes were made, we can infer the initial status of this edge to resolve this issue.
Interface changes:
The second semantic of `applyUpdates` is separated to `applyUpdatesPermissive`.
These changes enable DTU(Lazy) to use the first semantic if needed, which is quite useful in `transforms/utils`.
Reviewers: kuhar, brzycki, dmgreen, grosser
Reviewed By: brzycki
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D58170
llvm-svn: 354669
This patch accompanies the RFC posted here:
http://lists.llvm.org/pipermail/llvm-dev/2018-October/127239.html
This patch adds a new CallBr IR instruction to support asm-goto
inline assembly like gcc as used by the linux kernel. This
instruction is both a call instruction and a terminator
instruction with multiple successors. Only inline assembly
usage is supported today.
This also adds a new INLINEASM_BR opcode to SelectionDAG and
MachineIR to represent an INLINEASM block that is also
considered a terminator instruction.
There will likely be more bug fixes and optimizations to follow
this, but we felt it had reached a point where we would like to
switch to an incremental development model.
Patch by Craig Topper, Alexander Ivchenko, Mikhail Dvoretckii
Differential Revision: https://reviews.llvm.org/D53765
llvm-svn: 353563
DomTreeUpdater depends on headers from Analysis, but is in IR. This is a
layering violation since Analysis depends on IR. Relocate this code from IR
to Analysis to fix the layering violation.
llvm-svn: 353265
Juneyoung Lee