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New Loop Distribution pass

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Summary:
This implements the initial version as was proposed earlier this year
(http://lists.cs.uiuc.edu/pipermail/llvmdev/2015-January/080462.html).
Since then Loop Access Analysis was split out from the Loop Vectorizer
and was made into a separate analysis pass.  Loop Distribution becomes
the second user of this analysis.

The pass is off by default and can be enabled
with -enable-loop-distribution.  There is currently no notion of
profitability; if there is a loop with dependence cycles, the pass will
try to split them off from other memory operations into a separate loop.

I decided to remove the control-dependence calculation from this first
version.  This and the issues with the PDT are actively discussed so it
probably makes sense to treat it separately.  Right now I just mark all
terminator instruction required which keeps identical CFGs for each
distributed loop.  This seems to be working pretty well for 456.hmmer
where even though there is an empty if-then block in the distributed
loop initially, it gets completely removed.

The pass keeps DominatorTree and LoopInfo updated.  I've tested this
with -loop-distribute-verify with the testsuite where we distribute ~90
loops.  SimplifyLoop is violated in some cases and I have a FIXME
covering this.

Reviewers: hfinkel, nadav, aschwaighofer

Reviewed By: aschwaighofer

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8831

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237358 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Adam Nemet
2015-05-14 12:05:18 +00:00
parent 6a882f8907
commit dd469afe15
12 changed files with 1487 additions and 0 deletions
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9
lib/Transforms/IPO/PassManagerBuilder.cpp
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@@ -85,6 +85,10 @@ static cl::opt<bool> EnableLoopInterchange(
"enable-loopinterchange", cl::init(false), cl::Hidden,
cl::desc("Enable the new, experimental LoopInterchange Pass"));
static cl::opt<bool> EnableLoopDistribute(
"enable-loop-distribute", cl::init(false), cl::Hidden,
cl::desc("Enable the new, experimental LoopDistribution Pass"));
PassManagerBuilder::PassManagerBuilder() {
OptLevel = 2;
SizeLevel = 0;
@@ -320,6 +324,11 @@ void PassManagerBuilder::populateModulePassManager(
// on the rotated form.
MPM.add(createLoopRotatePass());
// Distribute loops to allow partial vectorization. I.e. isolate dependences
// into separate loop that would otherwise inhibit vectorization.
if (EnableLoopDistribute)
MPM.add(createLoopDistributePass());
MPM.add(createLoopVectorizePass(DisableUnrollLoops, LoopVectorize));
// FIXME: Because of #pragma vectorize enable, the passes below are always
// inserted in the pipeline, even when the vectorizer doesn't run (ex. when