[PATCH] D44880: [Hexagon] peel loops with runtime small trip counts

[Ikhlas Ajbar via Phabricator via llvm-commits]

iajbar created this revision.
iajbar added a reviewer: bcahoon.

We peel loops with small runtime trip count for hexagon only. We set PeelCount in HexagonTargetInfo.cpp and run computePeelCount() only when PeelCount is not set since it resets the PeelCount.


https://reviews.llvm.org/D44880

Files:
  lib/Target/Hexagon/HexagonTargetTransformInfo.cpp
  lib/Transforms/Scalar/LoopUnrollPass.cpp
  lib/Transforms/Utils/LoopUnrollPeel.cpp
  test/Transforms/LoopUnroll/Hexagon/peel-small-loop.ll


Index: test/Transforms/LoopUnroll/Hexagon/peel-small-loop.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopUnroll/Hexagon/peel-small-loop.ll
@@ -0,0 +1,38 @@
+; 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
+}
+
Index: lib/Transforms/Utils/LoopUnrollPeel.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnrollPeel.cpp
+++ lib/Transforms/Utils/LoopUnrollPeel.cpp
@@ -58,7 +58,7 @@
     "unroll-peel-max-count", cl::init(7), cl::Hidden,
     cl::desc("Max average trip count which will cause loop peeling."));
 
-static cl::opt<unsigned> UnrollForcePeelCount(
+cl::opt<unsigned> UnrollForcePeelCount(
     "unroll-force-peel-count", cl::init(0), cl::Hidden,
     cl::desc("Force a peel count regardless of profiling information."));
 
Index: lib/Transforms/Scalar/LoopUnrollPass.cpp
===================================================================
--- lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -144,6 +144,8 @@
                        cl::desc("Allows loops to be peeled when the dynamic "
                                 "trip count is known to be low."));
 
+extern cl::opt<unsigned> UnrollForcePeelCount;
+
 static cl::opt<bool> UnrollUnrollRemainder(
   "unroll-remainder", cl::Hidden,
   cl::desc("Allow the loop remainder to be unrolled."));
@@ -795,7 +797,10 @@
   }
 
   // 4th priority is loop peeling
-  computePeelCount(L, LoopSize, UP, TripCount, SE);
+  if (UP.PeelCount == 0 || UnrollForcePeelCount.getNumOccurrences() != 0)
+    // Only compute UP.PeelCount if the target or the user has not reset the
+    // default value 0.
+    computePeelCount(L, LoopSize, UP, TripCount, SE);
   if (UP.PeelCount) {
     UP.Runtime = false;
     UP.Count = 1;
Index: lib/Target/Hexagon/HexagonTargetTransformInfo.cpp
===================================================================
--- lib/Target/Hexagon/HexagonTargetTransformInfo.cpp
+++ lib/Target/Hexagon/HexagonTargetTransformInfo.cpp
@@ -41,6 +41,12 @@
 void HexagonTTIImpl::getUnrollingPreferences(Loop *L, ScalarEvolution &SE,
                                              TTI::UnrollingPreferences &UP) {
   UP.Runtime = UP.Partial = true;
+  if (SE.getSmallConstantTripCount(L) == 0 &&
+      SE.getSmallConstantMaxTripCount(L) > 0 &&
+      SE.getSmallConstantMaxTripCount(L) <= 5) {
+    UP.PeelCount = 2;
+    UP.AllowPeeling = true;
+  }
 }
 
 unsigned HexagonTTIImpl::getNumberOfRegisters(bool vector) const {


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