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Add loop trip count based heuristic for SCoP detection 

As we currently do not perform any optimizations that targets (or is
  even aware) small trip counts we will skip them when we count the
  loops in a region.

llvm-svn: 248119
This commit is contained in:
Johannes Doerfert 2015-09-20 14:56:54 +00:00
parent b276bde162
commit 7175bdfbe4
2 changed files with 112 additions and 3 deletions
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20
polly/lib/Analysis/ScopDetection.cpp
View File

@ -733,6 +733,22 @@ bool ScopDetection::isValidLoop(Loop *L, DetectionContext &Context) const {
return invalid<ReportLoopBound>(Context, /*Assert=*/true, L, LoopCount);
}
/// @brief Return the number of loops in @p L (incl. @p L) that have a trip
/// count that is not known to be less than 8.
static unsigned countBeneficialLoops(Loop *L, ScalarEvolution &SE) {
auto *TripCount = SE.getBackedgeTakenCount(L);
auto count = 1;
if (auto *TripCountC = dyn_cast<SCEVConstant>(TripCount))
if (TripCountC->getValue()->getZExtValue() < 8)
count -= 1;
for (auto &SubLoop : *L)
count += countBeneficialLoops(SubLoop, SE);
return count;
}
bool ScopDetection::hasMoreThanOneLoop(Region *R) const {
auto LoopNum = 0;
@ -745,9 +761,7 @@ bool ScopDetection::hasMoreThanOneLoop(Region *R) const {
for (auto &SubLoop : SubLoops)
if (R->contains(SubLoop)) {
LoopNum++;
if (SubLoop->getSubLoopsVector().size() > 0)
LoopNum++;
LoopNum += countBeneficialLoops(SubLoop, *SE);
if (LoopNum >= 2)
return true;

95
polly/test/ScopDetect/non-beneficial-loops-small-trip-count.ll Normal file
View File

@ -0,0 +1,95 @@
; RUN: opt %loadPolly -polly-detect -analyze < %s | FileCheck %s
;
; CHECK-NOT: Valid
;
; Do not consider this a SCoP as we do not perform any optimizations for
; loops with a small trip count.
;
; void f(int *A) {
; for (int i = 0; i < 4; i++)
; for (int j = 0; j < 4; j++)
; for (int k = 0; k < 4; k++)
; for (int l = 0; l < 4; l++)
; A[i] += A[i] * A[i - 1] + A[i + 1];
; }
;
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
define void @f(i32* %A) {
entry:
br label %for.cond
for.cond: ; preds = %for.inc.24, %entry
%indvars.iv = phi i64 [ %indvars.iv.next, %for.inc.24 ], [ 0, %entry ]
%exitcond5 = icmp ne i64 %indvars.iv, 4
br i1 %exitcond5, label %for.body, label %for.end.26
for.body: ; preds = %for.cond
br label %for.cond.1
for.cond.1: ; preds = %for.inc.21, %for.body
%j.0 = phi i32 [ 0, %for.body ], [ %inc22, %for.inc.21 ]
%exitcond2 = icmp ne i32 %j.0, 4
br i1 %exitcond2, label %for.body.3, label %for.end.23
for.body.3: ; preds = %for.cond.1
br label %for.cond.4
for.cond.4: ; preds = %for.inc.18, %for.body.3
%k.0 = phi i32 [ 0, %for.body.3 ], [ %inc19, %for.inc.18 ]
%exitcond1 = icmp ne i32 %k.0, 4
br i1 %exitcond1, label %for.body.6, label %for.end.20
for.body.6: ; preds = %for.cond.4
br label %for.cond.7
for.cond.7: ; preds = %for.inc, %for.body.6
%l.0 = phi i32 [ 0, %for.body.6 ], [ %inc, %for.inc ]
%exitcond = icmp ne i32 %l.0, 4
br i1 %exitcond, label %for.body.9, label %for.end
for.body.9: ; preds = %for.cond.7
%arrayidx = getelementptr inbounds i32, i32* %A, i64 %indvars.iv
%tmp = load i32, i32* %arrayidx, align 4
%tmp6 = add nsw i64 %indvars.iv, -1
%arrayidx11 = getelementptr inbounds i32, i32* %A, i64 %tmp6
%tmp7 = load i32, i32* %arrayidx11, align 4
%mul = mul nsw i32 %tmp, %tmp7
%tmp8 = add nuw nsw i64 %indvars.iv, 1
%arrayidx13 = getelementptr inbounds i32, i32* %A, i64 %tmp8
%tmp9 = load i32, i32* %arrayidx13, align 4
%add14 = add nsw i32 %mul, %tmp9
%arrayidx16 = getelementptr inbounds i32, i32* %A, i64 %indvars.iv
%tmp10 = load i32, i32* %arrayidx16, align 4
%add17 = add nsw i32 %tmp10, %add14
store i32 %add17, i32* %arrayidx16, align 4
br label %for.inc
for.inc: ; preds = %for.body.9
%inc = add nuw nsw i32 %l.0, 1
br label %for.cond.7
for.end: ; preds = %for.cond.7
br label %for.inc.18
for.inc.18: ; preds = %for.end
%inc19 = add nuw nsw i32 %k.0, 1
br label %for.cond.4
for.end.20: ; preds = %for.cond.4
br label %for.inc.21
for.inc.21: ; preds = %for.end.20
%inc22 = add nuw nsw i32 %j.0, 1
br label %for.cond.1
for.end.23: ; preds = %for.cond.1
br label %for.inc.24
for.inc.24: ; preds = %for.end.23
%indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
br label %for.cond
for.end.26: ; preds = %for.cond
ret void
}