Add -unroll-allow-partial command line option that enabled the loop unroller to
partially unroll a loop when fully unrolling would not fit under the threshold.
Patch by Mikael Lepistö.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@54160 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/LoopUnroll.cpp b/lib/Transforms/Scalar/LoopUnroll.cpp
index 492db4d..386b91c 100644
--- a/lib/Transforms/Scalar/LoopUnroll.cpp
+++ b/lib/Transforms/Scalar/LoopUnroll.cpp
@@ -33,6 +33,11 @@
UnrollCount("unroll-count", cl::init(0), cl::Hidden,
cl::desc("Use this unroll count for all loops, for testing purposes"));
+static cl::opt<bool>
+UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden,
+ cl::desc("Allows loops to be partially unrolled until "
+ "-unroll-threshold loop size is reached."));
+
namespace {
class VISIBILITY_HIDDEN LoopUnroll : public LoopPass {
public:
@@ -122,7 +127,8 @@
if (Count == 0) {
// Conservative heuristic: if we know the trip count, see if we can
// completely unroll (subject to the threshold, checked below); otherwise
- // don't unroll.
+ // try to find greatest modulo of the trip count which is still under
+ // threshold value.
if (TripCount != 0) {
Count = TripCount;
} else {
@@ -136,9 +142,25 @@
DOUT << " Loop Size = " << LoopSize << "\n";
uint64_t Size = (uint64_t)LoopSize*Count;
if (TripCount != 1 && Size > UnrollThreshold) {
- DOUT << " TOO LARGE TO UNROLL: "
- << Size << ">" << UnrollThreshold << "\n";
- return false;
+ DOUT << " Too large to fully unroll with count: " << Count
+ << " because size: " << Size << ">" << UnrollThreshold << "\n";
+ if (UnrollAllowPartial) {
+ // Reduce unroll count to be modulo of TripCount for partial unrolling
+ Count = UnrollThreshold / LoopSize;
+ while (Count != 0 && TripCount%Count != 0) {
+ Count--;
+ }
+ if (Count < 2) {
+ DOUT << " could not unroll partially\n";
+ return false;
+ } else {
+ DOUT << " partially unrolling with count: " << Count << "\n";
+ }
+ } else {
+ DOUT << " will not try to unroll partially because "
+ << "-unroll-allow-partial not given\n";
+ return false;
+ }
}
}