[llvm] r201867 - normalize the last delinearized dimension

[Sebastian Pop]

Author: spop
Date: Fri Feb 21 12:15:11 2014
New Revision: 201867

URL: http://llvm.org/viewvc/llvm-project?rev=201867&view=rev
Log:
normalize the last delinearized dimension

in the dependence test, we used to discard some information that the
delinearization provides: the size of the innermost dimension of an array,
i.e., the size of scalars stored in the array, and the remainder of the
delinearization that provides the offset from which the array reads start,
i.e., the base address of the array.

To avoid losing this data in the rest of the data dependence analysis, the fix
is to multiply the access function in the last delinearized dimension by its
size, effectively making the size of the last dimension to always be in bytes,
and then add the remainder of delinearization to the last subscript,
effectively making the last subscript start at the base address of the array.

Modified:
    llvm/trunk/lib/Analysis/DependenceAnalysis.cpp

Modified: llvm/trunk/lib/Analysis/DependenceAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/DependenceAnalysis.cpp?rev=201867&r1=201866&r2=201867&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/DependenceAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/DependenceAnalysis.cpp Fri Feb 21 12:15:11 2014
@@ -3189,8 +3189,8 @@ DependenceAnalysis::tryDelinearize(const
     return false;
 
   SmallVector<const SCEV *, 4> SrcSubscripts, DstSubscripts, SrcSizes, DstSizes;
-  SrcAR->delinearize(*SE, SrcSubscripts, SrcSizes);
-  DstAR->delinearize(*SE, DstSubscripts, DstSizes);
+  const SCEV *RemainderS = SrcAR->delinearize(*SE, SrcSubscripts, SrcSizes);
+  const SCEV *RemainderD = DstAR->delinearize(*SE, DstSubscripts, DstSizes);
 
   int size = SrcSubscripts.size();
   // Fail when there is only a subscript: that's a linearized access function.
@@ -3210,6 +3210,21 @@ DependenceAnalysis::tryDelinearize(const
     if (SrcSizes[i] != DstSizes[i])
       return false;
 
+  // When the difference in remainders is different than a constant it might be
+  // that the base address of the arrays is not the same.
+  const SCEV *DiffRemainders = SE->getMinusSCEV(RemainderS, RemainderD);
+  if (!isa<SCEVConstant>(DiffRemainders))
+    return false;
+
+  // Normalize the last dimension: integrate the size of the "scalar dimension"
+  // and the remainder of the delinearization.
+  DstSubscripts[size-1] = SE->getMulExpr(DstSubscripts[size-1],
+                                         DstSizes[size-1]);
+  SrcSubscripts[size-1] = SE->getMulExpr(SrcSubscripts[size-1],
+                                         SrcSizes[size-1]);
+  SrcSubscripts[size-1] = SE->getAddExpr(SrcSubscripts[size-1], RemainderS);
+  DstSubscripts[size-1] = SE->getAddExpr(DstSubscripts[size-1], RemainderD);
+
 #ifndef NDEBUG
   DEBUG(errs() << "\nSrcSubscripts: ");
   for (int i = 0; i < size; i++)