Generalize IVUsers to track arbitrary expressions rather than expressions

explicitly split into stride-and-offset pairs. Also, add the
ability to track multiple post-increment loops on the same expression.

This refines the concept of "normalizing" SCEV expressions used for
to post-increment uses, and introduces a dedicated utility routine for
normalizing and denormalizing expressions.

This fixes the expansion of expressions which are post-increment users
of more than one loop at a time. More broadly, this takes LSR another
step closer to being able to reason about more than one loop at a time.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100699 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/ScalarEvolutionNormalization.h

@@ -0,0 +1,78 @@
+//===- llvm/Analysis/ScalarEvolutionNormalization.h - See below -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines utilities for working with "normalized" ScalarEvolution
+// expressions.
+//
+// The following example illustrates post-increment uses and how normalized
+// expressions help.
+//
+//   for (i=0; i!=n; ++i) {
+//     ...
+//   }
+//   use(i);
+//
+// While the expression for most uses of i inside the loop is {0,+,1}<%L>, the
+// expression for the use of i outside the loop is {1,+,1}<%L>, since i is
+// incremented at the end of the loop body. This is inconveient, since it
+// suggests that we need two different induction variables, one that starts
+// at 0 and one that starts at 1. We'd prefer to be able to think of these as
+// the same induction variable, with uses inside the loop using the
+// "pre-incremented" value, and uses after the loop using the
+// "post-incremented" value.
+//
+// Expressions for post-incremented uses are represented as an expression
+// paired with a set of loops for which the expression is in "post-increment"
+// mode (there may be multiple loops).
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_SCALAREVOLUTION_NORMALIZATION_H
+#define LLVM_ANALYSIS_SCALAREVOLUTION_NORMALIZATION_H
+
+#include "llvm/ADT/SmallPtrSet.h"
+
+namespace llvm {
+
+class Instruction;
+class DominatorTree;
+class Loop;
+class ScalarEvolution;
+class SCEV;
+class Value;
+
+/// TransformKind - Different types of transformations that
+/// TransformForPostIncUse can do.
+enum TransformKind {
+  /// Normalize - Normalize according to the given loops.
+  Normalize,
+  /// NormalizeAutodetect - Detect post-inc opportunities on new expressions,
+  /// update the given loop set, and normalize.
+  NormalizeAutodetect,
+  /// Denormalize - Perform the inverse transform on the expression with the
+  /// given loop set.
+  Denormalize
+};
+
+/// PostIncLoopSet - A set of loops.
+typedef SmallPtrSet<const Loop *, 2> PostIncLoopSet;
+
+/// TransformForPostIncUse - Transform the given expression according to the
+/// given transformation kind.
+const SCEV *TransformForPostIncUse(TransformKind Kind,
+                                   const SCEV *S,
+                                   Instruction *User,
+                                   Value *OperandValToReplace,
+                                   PostIncLoopSet &Loops,
+                                   ScalarEvolution &SE,
+                                   DominatorTree &DT);
+
+}
+
+#endif