Commit Graph

7 Commits

Author SHA1 Message Date
Tobias Grosser 670a5d88a3 [tests] Do not emity binary bitcode to stdout in RegionInfo tests
llvm-svn: 309485
2017-07-29 09:58:43 +00:00
Tobias Grosser f818c3300b Revert "Fix PR 24415 (at least), by making our post-dominator tree behavior sane."
and also "clang-format GenericDomTreeConstruction.h, since the current
formatting makes it look like their is a bug in the loop indentation, and there
is not"

This reverts commit r296535.

There are still some open design questions which I would like to discuss. I
revert this for Daniel (who gave the OK), as he is on vacation.

llvm-svn: 296812
2017-03-02 21:08:37 +00:00
Daniel Berlin 03f6938edc Fix PR 24415 (at least), by making our post-dominator tree behavior sane.
Summary:
Currently, our post-dom tree tries to ignore and remove the effects of
infinite loops.  It fails miserably at this, because it tries to do it
ahead of time, and thus can only detect self-loops, and any other type
of infinite loop, it pretends doesn't exist at all.

This can, in a bunch of cases, lead to wrong answers and a completely
empty post-dom tree.

Wrong answer:

```
declare void foo()
define internal void @f() {
entry:
  br i1 undef, label %bb35, label %bb3.i

bb3.i:
  call void @foo()
  br label %bb3.i

bb35.loopexit3:
  br label %bb35

bb35:
  ret void
}
```
We get:
```
Inorder PostDominator Tree:
  [1]  <<exit node>> {0,7}
    [2] %bb35 {1,6}
      [3] %bb35.loopexit3 {2,3}
      [3] %entry {4,5}
```

This is a trivial modification of the testcase for PR 6047
Note that we pretend bb3.i doesn't exist.
We also pretend that bb35 post-dominates entry.

While it's true that it does not exit in a theoretical sense, it's not
really helpful to try to ignore the effect and pretend that bb35
post-dominates entry.  Worse, we pretend the infinite loop does
nothing (it's usually considered a side-effect), and doesn't even
exist, even when it calls a function.  Sadly, this makes it impossible
to use when you are trying to move code safely.  All compilers also
create virtual or real single exit nodes (including us), and connect
infinite loops there (which this patch does).  In fact, others have
worked around our behavior here, to the point of building their own
post-dom trees:
https://zneak.github.io/fcd/2016/02/17/structuring.html and pointing
out the region infrastructure is near-useless for them with postdom in
this state :(

Completely empty post-dom tree:
```
define void @spam()  {
bb:
  br label %bb1

bb1:                                              ; preds = %bb1, %bb
  br label %bb1

bb2:                                              ; No predecessors!
  ret void
}
```
Printing analysis 'Post-Dominator Tree Construction' for function 'foo':
=============================--------------------------------
Inorder PostDominator Tree:
  [1]  <<exit node>> {0,1}

:(

(note that even if you ignore the effects of infinite loops, bb2
should be present as an exit node that post-dominates nothing).

This patch changes post-dom to properly handle infinite loops and does
root finding during calculation to prevent empty tress in such cases.

We match gcc's (and the canonical theoretical) behavior for infinite
loops (find the backedge, connect it to the exit block).

Testcases coming as soon as i finish running this on a ton of random graphs :)

Reviewers: chandlerc, davide

Subscribers: bryant, llvm-commits

Differential Revision: https://reviews.llvm.org/D29705

llvm-svn: 296535
2017-02-28 22:57:50 +00:00
Jan Wen Voung 6dc3076080 Revert the test moves from 176733. Use "REQUIRES: asserts" instead.
llvm-svn: 176873
2013-03-12 16:27:52 +00:00
Jan Wen Voung 7857a64909 Disable statistics on Release builds and move tests that depend on -stats.
Summary:
Statistics are still available in Release+Asserts (any +Asserts builds),
and stats can also be turned on with LLVM_ENABLE_STATS.

Move some of the FastISel stats that were moved under DEBUG()
back out of DEBUG(), since stats are disabled across the board now.

Many tests depend on grepping "-stats" output.  Move those into
a orig_dir/Stats/. so that they can be marked as unsupported
when building without statistics.

Differential Revision: http://llvm-reviews.chandlerc.com/D486

llvm-svn: 176733
2013-03-08 22:56:31 +00:00
Chandler Carruth 5da53436d5 Convert the uses of '|&' to use '2>&1 |' instead, which works on old
versions of Bash. In addition, I can back out the change to the lit
built-in shell test runner to support this.

This should fix the majority of fallout on Darwin, but I suspect there
will be a few straggling issues.

llvm-svn: 159544
2012-07-02 18:37:59 +00:00
Tobias Grosser 336734aca6 Add new RegionInfo pass.
The RegionInfo pass detects single entry single exit regions in a function,
where a region is defined as any subgraph that is connected to the remaining
graph at only two spots.
Furthermore an hierarchical region tree is built.
Use it by calling "opt -regions analyze" or "opt -view-regions".

llvm-svn: 109089
2010-07-22 07:46:31 +00:00