[NFC][LoopInterchange] Clean up of Irrelevant dependency checking using isOuterMostDepPositive.

[ram-NK]

Summary

The isOuterMostDepPositive() was there to check the negative dependency ('>') of outermost loop.This checking was there before https://github.com/llvm/llvm-project/issues/56275. In https://github.com/llvm/llvm-project/issues/56275 patch, DependenceInfo will make the negative dependency to non-negative (if NeedsNormalize is true). In LoopInterchange, DependenceInfo is used with NeedsNormalize as true. So there will not be any negative dependency in dependency matrix (DepMatrix). So checking the isOuterMostDepPositive is irrelevant (it returns true for negative dependency only).

With this patch all test cases can be passed with negative dependencies. Existing test cases with negative dependency listed below.

1. pr56275.ll
2. profitability.ll
3. loop-interchange-optimization-remarks.ll
4. interchangeable.ll

[fhahn]

Could you please add a description/motivation and a test case?

[ram-NK]

In D132982#3760502, @fhahn wrote:

Could you please add a description/motivation and a test case?

I have added description in SUMMARY. Since it is a NFC, additional test cases are not needed.

[ram-NK]

In D132982#3762742, @ram-NK wrote:

In D132982#3760502, @fhahn wrote:

Could you please add a description/motivation and a test case?

I have added description in SUMMARY. Since it is a NFC, additional test cases are not needed.

@fhahn Could you get the chance to review the details and code ?

[congzhe]

LGTM but I'd suggest to wait a couple of days to see if people have other comments. @fhahn would you like to comment on this patch?

llvm/lib/Transforms/Scalar/LoopInterchange.cpp

 // A loop is moved from index 'from' to an index 'to'. Update the Dependence
 // matrix by exchanging the two columns.
 static void interChangeDependencies(CharMatrix &DepMatrix, unsigned FromIndx,
                                     unsigned ToIndx) {
   for (unsigned I = 0, E = DepMatrix.size(); I < E; ++I)
     std::swap(DepMatrix[I][ToIndx], DepMatrix[I][FromIndx]);
 }
 
-// Checks if outermost non '=','S'or'I' dependence in the dependence matrix is
-// '>'
-static bool isOuterMostDepPositive(CharMatrix &DepMatrix, unsigned Row,
-                                   unsigned Column) {
-  for (unsigned i = 0; i <= Column; ++i) {
-    if (DepMatrix[Row][i] == '<')
-      return false;
-    if (DepMatrix[Row][i] == '>')
-      return true;
-  }
-  // All dependencies were '=','S' or 'I'
-  return false;
-}
-
 // Checks if no dependence exist in the dependency matrix in Row before Column.
 static bool containsNoDependence(CharMatrix &DepMatrix, unsigned Row,
                                  unsigned Column) {
   for (unsigned i = 0; i < Column; ++i) {
     if (DepMatrix[Row][i] != '=' && DepMatrix[Row][i] != 'S' &&
         DepMatrix[Row][i] != 'I')
       return false;
   }
   return true;
 }
 
 static bool validDepInterchange(CharMatrix &DepMatrix, unsigned Row,
                                 unsigned OuterLoopId, char InnerDep,
                                 char OuterDep) {
-  if (isOuterMostDepPositive(DepMatrix, Row, OuterLoopId))
-    return false;
-
   if (InnerDep == OuterDep)
     return true;
 
   // It is legal to interchange if and only if after interchange no row has a
   // '>' direction as the leftmost non-'='.
 
   if (InnerDep == '=' || InnerDep == 'S' || InnerDep == 'I')
     return true;