Fix maxLoopDepth computation in ScopInfo

[dpeixott]

Summary

The max loop depth was incorrectly computed for scops that contain a
block from a loop but do not contain the entire loop. We need to
check that the full loop is contained in the block when computing
the max loop depth.

[jdoerfert]

LGTM

[grosser]

Yes, this looks good. I wonder in which context you run into this? Is it possible to provide a test case that covers this?

[grosser]

Also, the commit message is slightly inaccurate:

We need to check that the full loop is contained in the block when computing

in the _region_

[dpeixott]

Added test case and fixed commit message.

[dpeixott]

Tobi,

I added a test case and also an explanation in the commit message on when we can hit this problem.

These scops occur when a region containing an inner loop is expanded
to include some blocks from the outer loop, but it cannot be fully
expanded to contain the outer loop because the region containing the
outer loop is invalid.

lib/Analysis/ScopInfo.cpp

bool Scop::buildAliasGroups(AliasAnalysis &AA) {
 
   return Valid;
 }
 
 static unsigned getMaxLoopDepthInRegion(const Region &R, LoopInfo &LI) {
   unsigned MinLD = INT_MAX, MaxLD = 0;
   for (BasicBlock *BB : R.blocks()) {
     if (Loop *L = LI.getLoopFor(BB)) {
+      if (!R.contains(L))
+        continue;
       unsigned LD = L->getLoopDepth();
       MinLD = std::min(MinLD, LD);
       MaxLD = std::max(MaxLD, LD);
     }
   }
 
   // Handle the case that there is no loop in the SCoP first.
   if (MaxLD == 0)
void Scop::printStatements(raw_ostream &OS) const {
 
   OS.indent(4) << "}\n";
 }
 
 void Scop::print(raw_ostream &OS) const {
   OS.indent(4) << "Function: " << getRegion().getEntry()->getParent()->getName()
                << "\n";
   OS.indent(4) << "Region: " << getNameStr() << "\n";
+  OS.indent(4) << "Max Loop Depth:  " << getMaxLoopDepth() << "\n";
   printContext(OS.indent(4));
   printAliasAssumptions(OS);
   printStatements(OS.indent(4));
 }
 
 void Scop::dump() const { print(dbgs()); }
 
 isl_ctx *Scop::getIslCtx() const { return IslCtx; }

test/ScopInfo/max-loop-depth.ll

+; RUN: opt %loadPolly -polly-scops -analyze < %s | FileCheck %s
+;
+;    void bar();
+;    void foo(int *A, int *B, long int N, long int M) {
+;      for (long int j = 0; j < M; ++j) {
+;        bar();
+;        for (long int i = 0; i < N; ++i)
+;          A[i] += 1;
+;        for (long int i = 0; i < N; ++i)
+;          A[i] += 1;
+;      }
+;    }
+;
+; Test to check that the scop only counts loop depth for loops fully contained
+; in the scop.
+; CHECK: Max Loop Depth: 1
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @foo(i32* %A, i32* %B, i64 %N, i64 %M) {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc13, %entry
+  %j.0 = phi i64 [ 0, %entry ], [ %inc14, %for.inc13 ]
+  %cmp = icmp slt i64 %j.0, %M
+  br i1 %cmp, label %for.body, label %for.end15
+
+for.body:                                         ; preds = %for.cond
+  call void (...)* @bar() #2
+  br label %for.cond1
+
+for.cond1:                                        ; preds = %for.inc, %for.body
+  %i.0 = phi i64 [ 0, %for.body ], [ %inc, %for.inc ]
+  %cmp2 = icmp slt i64 %i.0, %N
+  br i1 %cmp2, label %for.body3, label %for.end
+
+for.body3:                                        ; preds = %for.cond1
+  %arrayidx = getelementptr inbounds i32* %A, i64 %i.0
+  %tmp = load i32* %arrayidx, align 4
+  %add = add nsw i32 %tmp, 1
+  store i32 %add, i32* %arrayidx, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body3
+  %inc = add nuw nsw i64 %i.0, 1
+  br label %for.cond1
+
+for.end:                                          ; preds = %for.cond1
+  br label %for.cond5
+
+for.cond5:                                        ; preds = %for.inc10, %for.end
+  %i4.0 = phi i64 [ 0, %for.end ], [ %inc11, %for.inc10 ]
+  %cmp6 = icmp slt i64 %i4.0, %N
+  br i1 %cmp6, label %for.body7, label %for.end12
+
+for.body7:                                        ; preds = %for.cond5
+  %arrayidx8 = getelementptr inbounds i32* %A, i64 %i4.0
+  %tmp1 = load i32* %arrayidx8, align 4
+  %add9 = add nsw i32 %tmp1, 1
+  store i32 %add9, i32* %arrayidx8, align 4
+  br label %for.inc10
+
+for.inc10:                                        ; preds = %for.body7
+  %inc11 = add nuw nsw i64 %i4.0, 1
+  br label %for.cond5
+
+for.end12:                                        ; preds = %for.cond5
+  br label %for.inc13
+
+for.inc13:                                        ; preds = %for.end12
+  %inc14 = add nuw nsw i64 %j.0, 1
+  br label %for.cond
+
+for.end15:                                        ; preds = %for.cond
+  ret void
+}
+
+declare void @bar(...) #1
+