Add -unroll-runtime for unrolling loops with run-time trip counts.
Patch by Brendon Cahoon!
This extends the existing LoopUnroll and LoopUnrollPass. Brendon
measured no regressions in the llvm test suite with -unroll-runtime
enabled. This implementation works by using the existing loop
unrolling code to unroll the loop by a power-of-two (default 8). It
generates an if-then-else sequence of code prior to the loop to
execute the extra iterations before entering the unrolled loop.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146245 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Utils/LoopUnroll.cpp b/lib/Transforms/Utils/LoopUnroll.cpp
index 62e4fa2..b96f14b 100644
--- a/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/lib/Transforms/Utils/LoopUnroll.cpp
@@ -135,7 +135,8 @@
/// This utility preserves LoopInfo. If DominatorTree or ScalarEvolution are
/// available it must also preserve those analyses.
bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
- unsigned TripMultiple, LoopInfo *LI, LPPassManager *LPM) {
+ bool AllowRuntime, unsigned TripMultiple,
+ LoopInfo *LI, LPPassManager *LPM) {
BasicBlock *Preheader = L->getLoopPreheader();
if (!Preheader) {
DEBUG(dbgs() << " Can't unroll; loop preheader-insertion failed.\n");
@@ -165,12 +166,6 @@
return false;
}
- // Notify ScalarEvolution that the loop will be substantially changed,
- // if not outright eliminated.
- ScalarEvolution *SE = LPM->getAnalysisIfAvailable<ScalarEvolution>();
- if (SE)
- SE->forgetLoop(L);
-
if (TripCount != 0)
DEBUG(dbgs() << " Trip Count = " << TripCount << "\n");
if (TripMultiple != 1)
@@ -188,6 +183,20 @@
// Are we eliminating the loop control altogether?
bool CompletelyUnroll = Count == TripCount;
+ // We assume a run-time trip count if the compiler cannot
+ // figure out the loop trip count and the unroll-runtime
+ // flag is specified.
+ bool RuntimeTripCount = (TripCount == 0 && Count > 0 && AllowRuntime);
+
+ if (RuntimeTripCount && !UnrollRuntimeLoopProlog(L, Count, LI, LPM))
+ return false;
+
+ // Notify ScalarEvolution that the loop will be substantially changed,
+ // if not outright eliminated.
+ ScalarEvolution *SE = LPM->getAnalysisIfAvailable<ScalarEvolution>();
+ if (SE)
+ SE->forgetLoop(L);
+
// If we know the trip count, we know the multiple...
unsigned BreakoutTrip = 0;
if (TripCount != 0) {
@@ -209,6 +218,8 @@
DEBUG(dbgs() << " with a breakout at trip " << BreakoutTrip);
} else if (TripMultiple != 1) {
DEBUG(dbgs() << " with " << TripMultiple << " trips per branch");
+ } else if (RuntimeTripCount) {
+ DEBUG(dbgs() << " with run-time trip count");
}
DEBUG(dbgs() << "!\n");
}
@@ -332,6 +343,10 @@
BasicBlock *Dest = Headers[j];
bool NeedConditional = true;
+ if (RuntimeTripCount && j != 0) {
+ NeedConditional = false;
+ }
+
// For a complete unroll, make the last iteration end with a branch
// to the exit block.
if (CompletelyUnroll && j == 0) {