[PATCH] D30161: [LoopUnrolling] Peel loops with invariant backedge Phi input
Max Kazantsev via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Feb 27 01:47:57 PST 2017
mkazantsev updated this revision to Diff 89849.
mkazantsev retitled this revision from "[LoopPeeling] Peel loops with invariant backedge Phi input" to "[LoopUnrolling] Peel loops with invariant backedge Phi input".
https://reviews.llvm.org/D30161
Files:
lib/Transforms/Utils/LoopUnrollPeel.cpp
test/Transforms/LoopUnroll/peel-loop-not-forced.ll
Index: test/Transforms/LoopUnroll/peel-loop-not-forced.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopUnroll/peel-loop-not-forced.ll
@@ -0,0 +1,24 @@
+; RUN: opt < %s -S -loop-unroll -indvars -loop-deletion -simplifycfg -instcombine | FileCheck %s
+
+define i32 @invariant_backedge_1(i32 %a, i32 %b) {
+; CHECK-LABEL: @invariant_backedge_1
+; CHECK: entry:
+; CHECK-NEXT: %0 = mul i32 %b, 999
+; CHECK-NEXT: %1 = add i32 %0, %a
+; CHECK-NEXT: ret i32 %1
+entry:
+ br label %loop
+
+loop:
+ %i = phi i32 [ 0, %entry ], [ %inc, %loop ]
+ %sum = phi i32 [ 0, %entry ], [ %incsum, %loop ]
+ %plus = phi i32 [ %a, %entry ], [ %b, %loop ]
+
+ %incsum = add i32 %sum, %plus
+ %inc = add i32 %i, 1
+ %cmp = icmp slt i32 %i, 1000
+ br i1 %cmp, label %loop, label %exit
+
+exit:
+ ret i32 %sum
+}
Index: lib/Transforms/Utils/LoopUnrollPeel.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnrollPeel.cpp
+++ lib/Transforms/Utils/LoopUnrollPeel.cpp
@@ -80,13 +80,16 @@
return;
}
+ // If the peeling is not allowed, bail.
+ if (!UP.AllowPeeling)
+ return;
+
// If we don't know the trip count, but have reason to believe the average
// trip count is low, peeling should be beneficial, since we will usually
// hit the peeled section.
// We only do this in the presence of profile information, since otherwise
// our estimates of the trip count are not reliable enough.
- if (BaseOnTripCount && UP.AllowPeeling &&
- L->getHeader()->getParent()->getEntryCount()) {
+ if (BaseOnTripCount && L->getHeader()->getParent()->getEntryCount()) {
Optional<unsigned> PeelCount = getLoopEstimatedTripCount(L);
if (!PeelCount)
return;
@@ -108,6 +111,31 @@
}
}
+ // Try to find a Phi node that has the same loop invariant as an input from
+ // its only back edge. If there is such Phi, peeling 1 iteration from the
+ // loop is profitable, because starting from 2nd iteration we will have an
+ // invariant instead of this Phi.
+ if (auto *BackEdge = L->getLoopLatch()) {
+ BasicBlock *Header = L->getHeader();
+ // Iterate over Phis to find one with invariant input on back edge.
+ bool FoundCandidate = false;
+ PHINode *Phi;
+ for (auto BI = Header->begin(); (Phi = dyn_cast<PHINode>(&*BI)); ++BI) {
+ Value *Input = Phi->getIncomingValueForBlock(BackEdge);
+ if (L->isLoopInvariant(Input)) {
+ FoundCandidate = true;
+ break;
+ }
+ }
+ if (FoundCandidate) {
+ DEBUG(dbgs() << "Peel one iteration to get rid of " << *Phi
+ << " because starting from 2nd iteration it is always"
+ << " an invariant\n");
+ UP.PeelCount = 1;
+ return;
+ }
+ }
+
return;
}
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