Summary:
JumpThreading for guards feature has been reverted at https://reviews.llvm.org/rL295200
due to the following problem: the feature used the following algorithm for detection of
diamond patters:
1. Find a block with 2 predecessors;
2. Check that these blocks have a common single parent;
3. Check that the parent's terminator is a branch instruction.
The problem is that these checks are insufficient. They may pass for a non-diamond
construction in case if those two predecessors are actually the same block. This may
happen if parent's terminator is a br (either conditional or unconditional) to a block
that ends with "switch" instruction with exactly two branches going to one block.
This patch re-enables the JumpThreading for guards and fixes this issue by adding the
check that those found predecessors are actually different blocks. This guarantees that
parent's terminator is a conditional branch with exactly 2 different successors, which
is now ensured by assertions. It also adds two more tests for this situation (with parent's
terminator being a conditional and an unconditional branch).
Patch by Max Kazantsev!
Reviewers: anna, sanjoy, reames
Reviewed By: sanjoy
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D30036
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295410 91177308-0d34-0410-b5e6-96231b3b80d8
This reverts commit r294617.
We fail on an assert while trying to get a condition from an
unconditional branch.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295200 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
This patch allows JumpThreading also thread through guards.
Virtually, guard(cond) is equivalent to the following construction:
if (cond) { do something } else {deoptimize}
Yet it is not explicitly converted into IFs before lowering.
This patch enables early threading through guards in simple cases.
Currently it covers the following situation:
if (cond1) {
// code A
} else {
// code B
}
// code C
guard(cond2)
// code D
If there is implication cond1 => cond2 or !cond1 => cond2, we can transform
this construction into the following:
if (cond1) {
// code A
// code C
} else {
// code B
// code C
guard(cond2)
}
// code D
Thus, removing the guard from one of execution branches.
Patch by Max Kazantsev!
Reviewers: reames, apilipenko, igor-laevsky, anna, sanjoy
Reviewed By: sanjoy
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D29620
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294617 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
These are good candidates for jump threading. This enables later opts
(such as InstCombine) to combine instructions from the selects with
instructions out of the selects. SimplifyCFG will fold the select
again if unfolding wasn't worth it.
Patch by James Molloy and Pablo Barrio.
Reviewers: rengolin, haicheng, sebpop
Subscribers: jojo, jmolloy, llvm-commits
Differential Revision: https://reviews.llvm.org/D26391
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286236 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
These are good candidates for jump threading. This enables later opts
(such as InstCombine) to combine instructions from the selects with
instructions out of the selects. SimplifyCFG will fold the select
again if unfolding wasn't worth it.
Patch by James Molloy and Pablo Barrio.
Reviewers: reames, bkramer, mcrosier, gberry, haicheng, jmolloy, sebpop
Subscribers: jojo, rengolin, llvm-commits
Differential Revision: https://reviews.llvm.org/D25477
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284971 91177308-0d34-0410-b5e6-96231b3b80d8
All of these existed because MSVC 2013 was unable to synthesize default
move ctors. We recently dropped support for it so all that error-prone
boilerplate can go.
No functionality change intended.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284721 91177308-0d34-0410-b5e6-96231b3b80d8
Currently the pass updates branch weights in the IR if the function has
any PGO info (entry frequency is set). However we could still have
regions of the CFG that does not have branch weights collected (e.g. a
cold region). In this case we'd use static estimates. Since static
estimates for branches are determined independently, they are
inconsistent. Updating them can "randomly" inflate block frequencies.
I've run into this in a completely cold loop of h264ref from
SPEC. -Rpass-with-hotness showed the loop to be completely cold during
inlining (before JT) but completely hot during vectorization (after JT).
The new testcase demonstrate the problem. We check array elements
against 1, 2 and 3 in a loop. The check against 3 is the loop-exiting
check. The block names should be self-explanatory.
In this example, jump threading incorrectly updates the weight of the
loop-exiting branch to 0, drastically inflating the frequency of the
loop (in the range of billions).
There is no run-time profile info for edges inside the loop, so branch
probabilities are estimated. These are the resulting branch and block
frequencies for the loop body:
check_1 (16)
(8) / |
eq_1 | (8)
\ |
check_2 (16)
(8) / |
eq_2 | (8)
\ |
check_3 (16)
(1) / |
(loop exit) | (15)
|
(back edge)
First we thread eq_1 -> check_2 to check_3. Frequencies are updated to
remove the frequency of eq_1 from check_2 and then from the false edge
leaving check_2. Changed frequencies are highlighted with * *:
check_1 (16)
(8) / |
eq_1~ | (8)
/ |
/ check_2 (*8*)
/ (8) / |
\ eq_2 | (*0*)
\ \ |
` --- check_3 (16)
(1) / |
(loop exit) | (15)
|
(back edge)
Next we thread eq_1 -> check_3 and eq_2 -> check_3 to check_1 as new
back edges. Frequencies are updated to remove the frequency of eq_1 and
eq_3 from check_3 and then the false edge leaving check_3 (changed
frequencies are highlighted with * *):
check_1 (16)
(8) / |
eq_1~ | (8)
/ |
/ check_2 (*8*)
/ (8) / |
/-- eq_2~ | (*0*)
(back edge) |
check_3 (*0*)
(*0*) / |
(loop exit) | (*0*)
|
(back edge)
As a result, the loop exit edge ends up with 0 frequency which in turn makes
the loop header to have maximum frequency.
There are a few potential problems here:
1. The profile data seems odd. There is a single profile sample of the
loop being entered. On the other hand, there are no weights inside the
loop.
2. Based on static estimation we shouldn't set edges to "extreme"
values, i.e. extremely likely or unlikely.
3. We shouldn't create profile metadata that is calculated from static
estimation. I am not sure what policy is but it seems to make sense to
treat profile metadata as something that is known to originate from
profiling. Estimated probabilities should only be reflected in BPI/BFI.
Any one of these would probably fix the immediate problem. I went for 3
because I think it's a good policy to have and added a FIXME about 2.
Differential Revision: https://reviews.llvm.org/D24118
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280713 91177308-0d34-0410-b5e6-96231b3b80d8
Besides a general consistently benefit, the extra layer of indirection
allows the mechanical part of https://reviews.llvm.org/D23256 that
requires touching every transformation and analysis to be factored out
cleanly.
Thanks to David for the suggestion.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278077 91177308-0d34-0410-b5e6-96231b3b80d8
What happened here is that in the new PM there is a bunch of new copying
(actually, moving) and so this reads the HasProfileData member in
situations where it used to not be read.
It used to only be read strictly in the "runOnFunction" method and its
callees, where is *is* initialized (even after my patch).
So this ends up being benign as far as functional behavior of the
compiler (since we set HasProfileData in the "runImpl" method before we
ever make decisions based on it).
It's awesome that UBSan caught this. It highlights one more thing to
watch out for when porting passes.
Sanitizer bot log was:
-- Testing: 17049 tests, 32 threads --
Testing: 0 .. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80..
FAIL: LLVM :: Transforms/JumpThreading/thread-loads.ll (15184 of 17049)
******************** TEST 'LLVM :: Transforms/JumpThreading/thread-loads.ll' FAILED ********************
Script:
--
/mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm_build_ubsan/./bin/opt < /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/test/Transforms/JumpThreading/thread-loads.ll -jump-threading -S | /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm_build_ubsan/./bin/FileCheck /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/test/Transforms/JumpThreading/thread-loads.ll
/mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm_build_ubsan/./bin/opt < /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/test/Transforms/JumpThreading/thread-loads.ll -passes=jump-threading -S | /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm_build_ubsan/./bin/FileCheck /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/test/Transforms/JumpThreading/thread-loads.ll
--
Exit Code: 2
Command Output (stderr):
--
/mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/include/llvm/Transforms/Scalar/JumpThreading.h:90:57: runtime error: load of value 136, which is not a valid value for type 'bool'
#0 0x2c33ba1 in llvm::JumpThreadingPass::JumpThreadingPass(llvm::JumpThreadingPass&&) /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/include/llvm/Transforms/Scalar/JumpThreading.h:90:57
#1 0x2bc88e4 in void llvm::PassManager<llvm::Function>::addPass<llvm::JumpThreadingPass>(llvm::JumpThreadingPass) /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/include/llvm/IR/PassManager.h:282:40
#2 0x2bb2682 in llvm::PassBuilder::parseFunctionPassName(llvm::PassManager<llvm::Function>&, llvm::StringRef) /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/lib/Passes/PassRegistry.def:133:1
#3 0x2bb4914 in llvm::PassBuilder::parseFunctionPassPipeline(llvm::PassManager<llvm::Function>&, llvm::StringRef&, bool, bool) /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/lib/Passes/PassBuilder.cpp:489:12
#4 0x2bb6f81 in llvm::PassBuilder::parsePassPipeline(llvm::PassManager<llvm::Module>&, llvm::StringRef, bool, bool) /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/lib/Passes/PassBuilder.cpp:674:10
#5 0x986690 in llvm::runPassPipeline(llvm::StringRef, llvm::LLVMContext&, llvm::Module&, llvm::TargetMachine*, llvm::tool_output_file*, llvm::StringRef, llvm::opt_tool::OutputKind, llvm::opt_tool::VerifierKind, bool, bool) /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/tools/opt/NewPMDriver.cpp:85:8
#6 0x9af25e in main /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/tools/opt/opt.cpp:468:12
#7 0x7fd7e27dbf44 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21f44)
#8 0x960157 in _start (/mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm_build_ubsan/bin/opt+0x960157)
FileCheck error: '-' is empty.
FileCheck command line: /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm_build_ubsan/./bin/FileCheck /mnt/b/sanitizer-buildbot3/sanitizer-x86_64-linux-fast/build/llvm/test/Transforms/JumpThreading/thread-loads.ll
--
********************
Testing: 0 .. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 80.. 90..
Testing Time: 128.90s
********************
Failing Tests (1):
LLVM :: Transforms/JumpThreading/thread-loads.ll
Expected Passes : 16725
Expected Failures : 129
Unsupported Tests : 194
Unexpected Failures: 1
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272616 91177308-0d34-0410-b5e6-96231b3b80d8
This reverts commit r272603 and adds a fix.
Big thanks to Davide for pointing me at r216244 which gives some insight
into how to fix this VS2013 issue. VS2013 can't synthesize a move
constructor. So the fix here is to add one explicitly to the
JumpThreadingPass class.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272607 91177308-0d34-0410-b5e6-96231b3b80d8
I've tested this locally with VS2015 and there are no issues there,
so this might be a VS2013 specific issue.
Thanks to Davide for the suggested fix.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272601 91177308-0d34-0410-b5e6-96231b3b80d8
This follows the approach in r263208 (for GVN) pretty closely:
- move the bulk of the body of the function to the new PM class.
- expose a runImpl method on the new-PM class that takes the IRUnitT and
pointers/references to any analyses and use that to implement the
old-PM class.
- use a private namespace in the header for stuff that used to be file
scope
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272597 91177308-0d34-0410-b5e6-96231b3b80d8
