Commit Graph

5 Commits

Author SHA1 Message Date
Florian Hahn 831a757728 [LoopInterchange] Preserve LoopInfo after interchanging.
LoopInterchange relies on LoopInfo being up-to-date, so we should
preserve it after interchanging. This patch updates restructureLoops to
move the BBs of the interchanged loops to the right place.

Reviewers: davide, efriedma, karthikthecool, mcrosier

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D45278

llvm-svn: 329264
2018-04-05 09:48:45 +00:00
Florian Hahn b79217077d [LoopInterchange] Update tests so DA can handle access after D35430.
I have taken the opportunity to simplify some tests slightly and move
parts around.

It also brings back a few IR checks for interchangable loops.

Reviewers: karthikthecool, sebpop, grosser

Reviewed By: sebpop

Differential Revision: https://reviews.llvm.org/D45207

llvm-svn: 329081
2018-04-03 16:37:58 +00:00
Sebastian Pop bf6e1c26cf DA: remove uses of GEP, only ask SCEV
It's been quite some time the Dependence Analysis (DA) is broken,
as it uses the GEP representation to "identify" multi-dimensional arrays.
It even wrongly detects multi-dimensional arrays in single nested loops:

from test/Analysis/DependenceAnalysis/Coupled.ll, example @couple6
;; for (long int i = 0; i < 50; i++) {
;; A[i][3*i - 6] = i;
;; *B++ = A[i][i];

DA used to detect two subscripts, which makes no sense in the LLVM IR
or in C/C++ semantics, as there are no guarantees as in Fortran of
subscripts not overlapping into a next array dimension:

maximum nesting levels = 1
SrcPtrSCEV = %A
DstPtrSCEV = %A
using GEPs
subscript 0
    src = {0,+,1}<nuw><nsw><%for.body>
    dst = {0,+,1}<nuw><nsw><%for.body>
    class = 1
    loops = {1}
subscript 1
    src = {-6,+,3}<nsw><%for.body>
    dst = {0,+,1}<nuw><nsw><%for.body>
    class = 1
    loops = {1}
Separable = {}
Coupled = {1}

With the current patch, DA will correctly work on only one dimension:

maximum nesting levels = 1
SrcSCEV = {(-2424 + %A)<nsw>,+,1212}<%for.body>
DstSCEV = {%A,+,404}<%for.body>
subscript 0
    src = {(-2424 + %A)<nsw>,+,1212}<%for.body>
    dst = {%A,+,404}<%for.body>
    class = 1
    loops = {1}
Separable = {0}
Coupled = {}

This change removes all uses of GEP from DA, and we now only rely
on the SCEV representation.

The patch does not turn on -da-delinearize by default, and so the DA analysis
will be more conservative in the case of multi-dimensional memory accesses in
nested loops.

I disabled some interchange tests, as the DA is not able to disambiguate
the dependence anymore. To make DA stronger, we may need to
compute a bound on the number of iterations based on the access functions
and array dimensions.

The patch cleans up all the CHECKs in test/Transforms/LoopInterchange/*.ll to
avoid checking for snippets of LLVM IR: this form of checking is very hard to
maintain. Instead, we now check for output of the pass that are more meaningful
than dozens of lines of LLVM IR. Some tests now require -debug messages and thus
only enabled with asserts.

Patch written by Sebastian Pop and Aditya Kumar.

Differential Revision: https://reviews.llvm.org/D35430

llvm-svn: 326837
2018-03-06 21:55:59 +00:00
Florian Hahn c6296fea3f [LoopInterchange] Incrementally update the dominator tree.
We can use incremental dominator tree updates to avoid re-calculating
the dominator tree after interchanging 2 loops.

Reviewers: dmgreen, kuhar

Reviewed By: kuhar

Differential Revision: https://reviews.llvm.org/D43176

llvm-svn: 325122
2018-02-14 13:13:15 +00:00
David Green 907b60fbba [LoopInterchange] Fix phi node ordering miscompile.
The way that splitInnerLoopHeader splits blocks requires that
the induction PHI will be the first PHI in the inner loop
header. This makes sure that is actually the case when there
are both IV and reduction phis.

Differential Revision: https://reviews.llvm.org/D38682

llvm-svn: 316261
2017-10-21 13:58:37 +00:00