Loop Unroll: add options and tweak to make Partial unrolling more useful
1. Add FullUnrollMaxCount option that works like MaxCount, but also limits
the unroll count for fully unrolled loops. So if a loop has an iteration
count over this, it won't fully unroll.
2. Add CLI options for MaxCount and the new option, so they can be tested
(plus a test).
3. Make partial unrolling obey MaxCount.
An example use-case (the out of tree one this is originally designed for) is
a target’s TTI can analyze a loop and decide on a max unroll count separate
from the size threshold, e.g. based on register pressure, then constrain
LoopUnroll to not exceed that, regardless of the size of the unrolled loop.
llvm-svn: 265562
diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index e5a9513..01a8ad8 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -65,6 +65,15 @@
cl::desc("Use this unroll count for all loops including those with "
"unroll_count pragma values, for testing purposes"));
+static cl::opt<unsigned>
+UnrollMaxCount("unroll-max-count", cl::Hidden,
+ cl::desc("Set the max unroll count for partial and runtime unrolling, for"
+ "testing purposes"));
+
+static cl::opt<unsigned>
+UnrollFullMaxCount("unroll-full-max-count", cl::Hidden,
+ cl::desc("Set the max unroll count for full unrolling, for testing purposes"));
+
static cl::opt<bool>
UnrollAllowPartial("unroll-allow-partial", cl::Hidden,
cl::desc("Allows loops to be partially unrolled until "
@@ -107,6 +116,7 @@
UP.PartialOptSizeThreshold = UP.OptSizeThreshold;
UP.Count = 0;
UP.MaxCount = UINT_MAX;
+ UP.FullUnrollMaxCount = UINT_MAX;
UP.Partial = false;
UP.Runtime = false;
UP.AllowExpensiveTripCount = false;
@@ -138,6 +148,10 @@
UP.DynamicCostSavingsDiscount = UnrollDynamicCostSavingsDiscount;
if (UnrollCount.getNumOccurrences() > 0)
UP.Count = UnrollCount;
+ if (UnrollMaxCount.getNumOccurrences() > 0)
+ UP.MaxCount = UnrollMaxCount;
+ if (UnrollFullMaxCount.getNumOccurrences() > 0)
+ UP.FullUnrollMaxCount = UnrollFullMaxCount;
if (UnrollAllowPartial.getNumOccurrences() > 0)
UP.Partial = UnrollAllowPartial;
if (UnrollRuntime.getNumOccurrences() > 0)
@@ -566,6 +580,7 @@
Count = TripCount == 0 ? DefaultUnrollRuntimeCount : TripCount;
if (TripCount && Count > TripCount)
Count = TripCount;
+ Count = std::min(Count, UP.FullUnrollMaxCount);
unsigned NumInlineCandidates;
bool NotDuplicatable;
@@ -633,10 +648,12 @@
<< "-unroll-allow-partial not given\n");
return false;
}
- if (UP.PartialThreshold != NoThreshold &&
- UnrolledSize > UP.PartialThreshold) {
+ if (UP.PartialThreshold != NoThreshold && Count > 1) {
// Reduce unroll count to be modulo of TripCount for partial unrolling.
- Count = (std::max(UP.PartialThreshold, 3u) - 2) / (LoopSize - 2);
+ if (UnrolledSize > UP.PartialThreshold)
+ Count = (std::max(UP.PartialThreshold, 3u) - 2) / (LoopSize - 2);
+ if (Count > UP.MaxCount)
+ Count = UP.MaxCount;
while (Count != 0 && TripCount % Count != 0)
Count--;
if (AllowRuntime && Count <= 1) {