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Add -unroll-allow-partial command line option that enabled the loop unroller to

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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
This commit is contained in:
Matthijs Kooijman 2008-07-29 13:21:23 +00:00
parent 477f5a2f11
commit 75cf9cc527
2 changed files with 41 additions and 4 deletions
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30
lib/Transforms/Scalar/LoopUnroll.cpp
View File

@ -33,6 +33,11 @@ static cl::opt<unsigned>
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 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
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 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
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;
}
}
}

15
test/Transforms/LoopUnroll/partial.ll Normal file
View File

@ -0,0 +1,15 @@
; RUN: llvm-as < %s | opt -debug -loop-unroll |& grep {will not try to unroll partially because}
; RUN: llvm-as < %s | opt -debug -loop-unroll -unroll-allow-partial |& grep {partially unrolling with count}
; RUN: llvm-as < %s | opt -debug -loop-unroll -unroll-allow-partial -unroll-threshold=3 |& grep {could not unroll partially}
define i32 @main() {
entry:
br label %no_exit
no_exit: ; preds = %no_exit, %entry
%indvar = phi i32 [ 0, %entry ], [ %indvar.next, %no_exit ] ; <i32> [#uses=1]
%indvar.next = add i32 %indvar, 1 ; <i32> [#uses=2]
%exitcond = icmp ne i32 %indvar.next, 100 ; <i1> [#uses=1]
br i1 %exitcond, label %no_exit, label %loopexit
loopexit: ; preds = %no_exit
ret i32 0
}