Merging identical blocks when it doesn't reduce fallthrough. It is common for
the blocks created from critical edge splitting to be identical. We would like
to merge these blocks whenever doing so would not reduce fallthrough.
llvm-svn: 299890
Summary: D25742 improved the precision of debug locations for PGO by removing debug locations from common tail when tail-merging. However, if identical insturctions that are merged into a common tail have the same debug locations, there's no need to remove them. This patch creates a merged debug location of identical instructions across SameTails and assign it to the instruction in the common tail, so that the debug locations are maintained if they are same across identical instructions.
Reviewers: aprantl, probinson, MatzeB, rob.lougher
Reviewed By: aprantl
Subscribers: andreadb, llvm-commits
Differential Revision: https://reviews.llvm.org/D30226
llvm-svn: 297805
Summary:
Currently, BranchFolder drops DebugLoc for branch instructions in some places. For example, for the test code attached, the branch instruction of 'entry' block has a DILocation of
```
!12 = !DILocation(line: 6, column: 3, scope: !11)
```
, but this information is gone when then block is lowered because BranchFolder misses it. This patch is a fix for this issue.
Reviewers: qcolombet, aprantl, craig.topper, MatzeB
Reviewed By: aprantl
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D29902
llvm-svn: 295684
This reverts r294348, which removed support for conditional tail calls
due to the PR above. It fixes the PR by marking live registers as
implicitly used and defined by the now predicated tailcall. This is
similar to how IfConversion predicates instructions.
Differential Revision: https://reviews.llvm.org/D29856
llvm-svn: 295262
Summary:
Blocks ending in unreachable are typically cold because they end the
program or throw an exception, so merging them with other identical
blocks is usually profitable because it reduces the size of cold code.
MachineBlockPlacement generally does not arrange to fall through to such
blocks, so commoning these blocks will not introduce additional
unconditional branches.
Reviewers: hans, iteratee, haicheng
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D29153
llvm-svn: 295105
They are currently modelled incorrectly (as calls, which clobber
registers, confusing e.g. Machine Copy Propagation).
Reverting until we figure out the proper solution.
llvm-svn: 294348
When choosing the best successor for a block, ordinarily we would have preferred
a block that preserves the CFG unless there is a strong probability the other
direction. For small blocks that can be duplicated we now skip that requirement
as well, subject to some simple frequency calculations.
Differential Revision: https://reviews.llvm.org/D28583
llvm-svn: 293716
Summary:
This commits moves skipDebugInstructionsForward and
skipDebugInstructionsBackward from lib/CodeGen/IfConversion.cpp
to include/llvm/CodeGen/MachineBasicBlock.h and updates
some codgen files to use them.
This refactoring was suggested in https://reviews.llvm.org/D27688
and I thought it's best to do the refactoring in a separate
review, but I could also put both changes in a single review
if that's preferred.
Also, the names for the functions aren't the snappiest and
I would be happy to rename them if anybody has suggestions.
Reviewers: eli.friedman, iteratee, aprantl, MatzeB
Subscribers: MatzeB, llvm-commits
Differential Revision: https://reviews.llvm.org/D27782
llvm-svn: 289933
This reapplies revision 285093. Original commit message:
The branch folding pass tail merges blocks into a common-tail. However, the
tail retains the debug information from one of the original inputs to the
merge (chosen randomly). This is a problem for sampled-based PGO, as hits
on the common-tail will be attributed to whichever block was chosen,
irrespective of which path was actually taken to the common-tail.
This patch fixes the issue by nulling the debug location for the common-tail.
Differential Revision: https://reviews.llvm.org/D25742
llvm-svn: 285212
This reverts r285093, as it caused unexpected buildbot failures on
clang-ppc64le-linux, clang-ppc64be-linux, clang-ppc64be-linux-multistage
and clang-ppc64be-linux-lnt. Failing test ubsan/TestCases/TypeCheck/vptr.cpp.
llvm-svn: 285110
The branch folding pass tail merges blocks into a common-tail. However, the
tail retains the debug information from one of the original inputs to the
merge (chosen randomly). This is a problem for sampled-based PGO, as hits
on the common-tail will be attributed to whichever block was chosen,
irrespective of which path was actually taken to the common-tail.
This patch fixes the issue by nulling the debug location for the common-tail.
Differential Revision: https://reviews.llvm.org/D25742
llvm-svn: 285093
Branch folder removes implicit defs if they are the only non-branching
instructions in a block, and the branches do not use the defined registers.
The problem is that in some cases these implicit defs are required for
the liveness information to be correct.
Differential Revision: https://reviews.llvm.org/D25478
llvm-svn: 284036
It is legal to merge instructions with different undef flags; However we
must drop the undef flag from the merged instruction if it isn't present
everywhere.
This fixes http://llvm.org/PR30199
llvm-svn: 281957
When branching to a block that immediately tail calls, it is possible to fold
the call directly into the branch if the call is direct and there is no stack
adjustment, saving one byte.
Example:
define void @f(i32 %x, i32 %y) {
entry:
%p = icmp eq i32 %x, %y
br i1 %p, label %bb1, label %bb2
bb1:
tail call void @foo()
ret void
bb2:
tail call void @bar()
ret void
}
before:
f:
movl 4(%esp), %eax
cmpl 8(%esp), %eax
jne .LBB0_2
jmp foo
.LBB0_2:
jmp bar
after:
f:
movl 4(%esp), %eax
cmpl 8(%esp), %eax
jne bar
.LBB0_1:
jmp foo
I don't expect any significant size savings from this (on a Clang bootstrap I
saw 288 bytes), but it does make the code a little tighter.
This patch only does 32-bit, but 64-bit would work similarly.
Differential Revision: https://reviews.llvm.org/D24108
llvm-svn: 280832
This is prep work for allowing the threshold to be different during layout,
and to enforce a single threshold between merging and duplicating during
layout. No observable change intended.
llvm-svn: 279117
To fix PR28014, this patch restricts tail merging to blocks that belong to the
same loop after MBP.
Differential Revision: https://reviews.llvm.org/D23191
llvm-svn: 278463
This change makes it possible for tail-duplication and tail-merging to
be disjoint. By being less aggressive when merging during layout, there are no
overlapping cases between tail-duplication and tail-merging, provided the
thresholds are disjoint.
There is a remaining TODO to benchmark the succ_size() test for non-layout tail
merging.
llvm-svn: 278265
Use LivePhysRegs with a backwards walking algorithm to update live in
lists, this way the results do not depend on the presence of kill flags
anymore.
This patch also reduces the number of registers added as live-in.
Previously all pristine registers as well as all sub registers of a
super register were added resulting in unnecessarily large live in
lists. This fixed https://llvm.org/PR25263.
Differential Revision: http://reviews.llvm.org/D22027
llvm-svn: 275201
Blocks to be tail-merged may share more than one successor. Correct the
comment to state that they share a specific successor, SuccBB, rather
than a single successor, which is not true.
llvm-svn: 275104
Tail merge was making the assumption that a layout successor or
predecessor was always a cfg successor/predecessor. Remove that
assumption. Changes to tests are necessary because the errant cfg edges
were preventing optimizations.
llvm-svn: 273700
This reapplies commit r271930, r271915, r271923. They hit a bug in
Thumb which is fixed in r272258 now.
The original message:
The code layout that TailMerging (inside BranchFolding) works on is not the
final layout optimized based on the branch probability. Generally, after
BlockPlacement, many new merging opportunities emerge.
This patch calls Tail Merging after MBP and calls MBP again if Tail Merging
merges anything.
llvm-svn: 272267
The code layout that TailMerging (inside BranchFolding) works on is not the
final layout optimized based on the branch probability. Generally, after
BlockPlacement, many new merging opportunities emerge.
This patch calls Tail Merging after MBP and calls MBP again if Tail Merging
merges anything.
Differential Revision: http://reviews.llvm.org/D20276
llvm-svn: 271925
Move the register stackification and coloring passes to run very late, after
PEI, tail duplication, and most other passes. This means that all code emitted
and expanded by those passes is now exposed to these passes. This also
eliminates the need for prologue/epilogue code to be manually stackified,
which significantly simplifies the code.
This does require running LiveIntervals a second time. It's useful to think
of these late passes not as late optimization passes, but as a domain-specific
compression algorithm based on knowledge of liveness information. It's used to
compress the code after all conventional optimizations are complete, which is
why it uses LiveIntervals at a phase when actual optimization passes don't
typically need it.
Differential Revision: http://reviews.llvm.org/D20075
llvm-svn: 269012
Many files include Passes.h but only a fraction needs to know about the
TargetPassConfig class. Move it into an own header. Also rename
Passes.cpp to TargetPassConfig.cpp while we are at it.
llvm-svn: 269011
The original commit was reverted because of a buildbot problem with LazyCallGraph::SCC handling (not related to the OptBisect handling).
Differential Revision: http://reviews.llvm.org/D19172
llvm-svn: 267231
This patch implements a optimization bisect feature, which will allow optimizations to be selectively disabled at compile time in order to track down test failures that are caused by incorrect optimizations.
The bisection is enabled using a new command line option (-opt-bisect-limit). Individual passes that may be skipped call the OptBisect object (via an LLVMContext) to see if they should be skipped based on the bisect limit. A finer level of control (disabling individual transformations) can be managed through an addition OptBisect method, but this is not yet used.
The skip checking in this implementation is based on (and replaces) the skipOptnoneFunction check. Where that check was being called, a new call has been inserted in its place which checks the bisect limit and the optnone attribute. A new function call has been added for module and SCC passes that behaves in a similar way.
Differential Revision: http://reviews.llvm.org/D19172
llvm-svn: 267022
If the lhs is evaluated before the rhs, FuncletI's operator-> can trigger the
assert(isHandleInSync() && "invalid iterator access!");
at include/llvm/ADT/DenseMap.h:1061. (Happens e.g. when compiled with GCC 6.)
Differential Revision: http://reviews.llvm.org/D18440
llvm-svn: 265024
Summary:
Removing MMOs is not our prefer behavior any more.
Reviewers: mcrosier, reames
Differential Revision: http://reviews.llvm.org/D17668
llvm-svn: 262580
Change MachineInstr API to prefer MachineInstr& over MachineInstr*
whenever the parameter is expected to be non-null. Slowly inching
toward being able to fix PR26753.
llvm-svn: 262149
Change TargetInstrInfo API to take `MachineInstr&` instead of
`MachineInstr*` in the functions related to predicated instructions
(I'll try to come back later and get some of the rest). All of these
functions require non-null parameters already, so references are more
clear. As a bonus, this happens to factor away a host of implicit
iterator => pointer conversions.
No functionality change intended.
llvm-svn: 261605
Kyle Butt