[polly] r248119 - Add loop trip count based heuristic for SCoP detection
Johannes Doerfert via llvm-commits
llvm-commits at lists.llvm.org
Sun Sep 20 07:56:54 PDT 2015
Author: jdoerfert
Date: Sun Sep 20 09:56:54 2015
New Revision: 248119
URL: http://llvm.org/viewvc/llvm-project?rev=248119&view=rev
Log:
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.
Added:
polly/trunk/test/ScopDetect/non-beneficial-loops-small-trip-count.ll
Modified:
polly/trunk/lib/Analysis/ScopDetection.cpp
Modified: polly/trunk/lib/Analysis/ScopDetection.cpp
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/Analysis/ScopDetection.cpp?rev=248119&r1=248118&r2=248119&view=diff
==============================================================================
--- polly/trunk/lib/Analysis/ScopDetection.cpp (original)
+++ polly/trunk/lib/Analysis/ScopDetection.cpp Sun Sep 20 09:56:54 2015
@@ -733,6 +733,22 @@ bool ScopDetection::isValidLoop(Loop *L,
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(R
for (auto &SubLoop : SubLoops)
if (R->contains(SubLoop)) {
- LoopNum++;
- if (SubLoop->getSubLoopsVector().size() > 0)
- LoopNum++;
+ LoopNum += countBeneficialLoops(SubLoop, *SE);
if (LoopNum >= 2)
return true;
Added: polly/trunk/test/ScopDetect/non-beneficial-loops-small-trip-count.ll
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/test/ScopDetect/non-beneficial-loops-small-trip-count.ll?rev=248119&view=auto
==============================================================================
--- polly/trunk/test/ScopDetect/non-beneficial-loops-small-trip-count.ll (added)
+++ polly/trunk/test/ScopDetect/non-beneficial-loops-small-trip-count.ll Sun Sep 20 09:56:54 2015
@@ -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
+}
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