[llvm] r328854 - peel loops with runtime small trip counts

[Ikhlas Ajbar via llvm-commits]

Author: iajbar
Date: Thu Mar 29 20:05:34 2018
New Revision: 328854

URL: http://llvm.org/viewvc/llvm-project?rev=328854&view=rev
Log:
peel loops with runtime small trip counts

For Hexagon, peeling loops with small runtime trip count is beneficial for our
benchmarks. We set PeelCount in HexagonTargetInfo.cpp and we use PeelCount set
by the target for computing the desired peel count.

Differential Revision: https://reviews.llvm.org/D44880

Added:
    llvm/trunk/test/Transforms/LoopUnroll/Hexagon/
    llvm/trunk/test/Transforms/LoopUnroll/Hexagon/peel-small-loop.ll
Modified:
    llvm/trunk/lib/Target/Hexagon/HexagonTargetTransformInfo.cpp
    llvm/trunk/lib/Transforms/Utils/LoopUnrollPeel.cpp

Modified: llvm/trunk/lib/Target/Hexagon/HexagonTargetTransformInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Hexagon/HexagonTargetTransformInfo.cpp?rev=328854&r1=328853&r2=328854&view=diff
==============================================================================
--- llvm/trunk/lib/Target/Hexagon/HexagonTargetTransformInfo.cpp (original)
+++ llvm/trunk/lib/Target/Hexagon/HexagonTargetTransformInfo.cpp Thu Mar 29 20:05:34 2018
@@ -44,6 +44,14 @@ HexagonTTIImpl::getPopcntSupport(unsigne
 void HexagonTTIImpl::getUnrollingPreferences(Loop *L, ScalarEvolution &SE,
                                              TTI::UnrollingPreferences &UP) {
   UP.Runtime = UP.Partial = true;
+  // Only try to peel innermost loops with small runtime trip counts.
+  if (L && L->empty() &&
+      SE.getSmallConstantTripCount(L) == 0 &&
+      SE.getSmallConstantMaxTripCount(L) > 0 &&
+      SE.getSmallConstantMaxTripCount(L) <= 5) {
+    UP.PeelCount = 2;
+    UP.AllowPeeling = true;
+  }
 }
 
 bool HexagonTTIImpl::shouldFavorPostInc() const {

Modified: llvm/trunk/lib/Transforms/Utils/LoopUnrollPeel.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopUnrollPeel.cpp?rev=328854&r1=328853&r2=328854&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/LoopUnrollPeel.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/LoopUnrollPeel.cpp Thu Mar 29 20:05:34 2018
@@ -221,6 +221,9 @@ void llvm::computePeelCount(Loop *L, uns
                             TargetTransformInfo::UnrollingPreferences &UP,
                             unsigned &TripCount, ScalarEvolution &SE) {
   assert(LoopSize > 0 && "Zero loop size is not allowed!");
+  // Save the UP.PeelCount value set by the target in
+  // TTI.getUnrollingPreferences or by the flag -unroll-peel-count.
+  unsigned TargetPeelCount = UP.PeelCount;
   UP.PeelCount = 0;
   if (!canPeel(L))
     return;
@@ -240,7 +243,9 @@ void llvm::computePeelCount(Loop *L, uns
     SmallDenseMap<PHINode *, unsigned> IterationsToInvariance;
     // Now go through all Phis to calculate their the number of iterations they
     // need to become invariants.
-    unsigned DesiredPeelCount = 0;
+    // Start the max computation with the UP.PeelCount value set by the target
+    // in TTI.getUnrollingPreferences or by the flag -unroll-peel-count.
+    unsigned DesiredPeelCount = TargetPeelCount;
     BasicBlock *BackEdge = L->getLoopLatch();
     assert(BackEdge && "Loop is not in simplified form?");
     for (auto BI = L->getHeader()->begin(); isa<PHINode>(&*BI); ++BI) {

Added: llvm/trunk/test/Transforms/LoopUnroll/Hexagon/peel-small-loop.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/Hexagon/peel-small-loop.ll?rev=328854&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopUnroll/Hexagon/peel-small-loop.ll (added)
+++ llvm/trunk/test/Transforms/LoopUnroll/Hexagon/peel-small-loop.ll Thu Mar 29 20:05:34 2018
@@ -0,0 +1,37 @@
+; RUN: opt -loop-unroll -mtriple=hexagon -S < %s | FileCheck %s
+; Check that the loop is peeled twice for Hexagon.
+; CHECK: while.body.peel
+; CHECK: while.body.peel2
+
+%struct.STREAM = type { %union.anon, i32, i32 }
+%union.anon = type { i32* }
+
+define void @function(%struct.STREAM* nocapture readonly %b) local_unnamed_addr {
+entry:
+  %bitPtr3 = getelementptr inbounds %struct.STREAM, %struct.STREAM* %b, i32 0, i32 2
+  %0 = load i32, i32* %bitPtr3, align 4
+  %cmp11 = icmp ult i32 %0, 32
+  br i1 %cmp11, label %while.body.preheader, label %do.end
+
+while.body.preheader:
+  %value2 = getelementptr inbounds %struct.STREAM, %struct.STREAM* %b, i32 0, i32 1
+  %1 = load i32, i32* %value2, align 4
+  %w = getelementptr inbounds %struct.STREAM, %struct.STREAM* %b, i32 0, i32 0, i32 0
+  %2 = load i32*, i32** %w, align 4
+  br label %while.body
+
+while.body:
+  %bitPtr.014 = phi i32 [ %add, %while.body ], [ %0, %while.body.preheader ]
+  %value.013 = phi i32 [ %shl, %while.body ], [ %1, %while.body.preheader ]
+  %ptr.012 = phi i32* [ %incdec.ptr, %while.body ], [ %2, %while.body.preheader ]
+  %add = add nuw i32 %bitPtr.014, 8
+  %shr = lshr i32 %value.013, 24
+  %incdec.ptr = getelementptr inbounds i32, i32* %ptr.012, i32 1
+  store i32 %shr, i32* %ptr.012, align 4
+  %shl = shl i32 %value.013, 8
+  %cmp = icmp ult i32 %add, 17
+  br i1 %cmp, label %while.body, label %do.end
+
+do.end:
+  ret void
+}