From 699db99c1a356eaa407ee03ebdf8553853d82bbd Mon Sep 17 00:00:00 2001
From: Andreas Bolka <a@bolka.at>
Date: Fri, 7 Aug 2009 18:23:41 +0000
Subject: [PATCH] SIV/MIV classification for LDA.

LoopDependenceAnalysis::getLoops is currently O(N*M) for a loop-nest of
depth N and a compound SCEV of M atomic SCEVs. As both N and M will
typically be very small, this should not be a problem. If it turns out
to be one, rewriting getLoops as SCEVVisitor will reduce complexity to
O(M).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78394 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../llvm/Analysis/LoopDependenceAnalysis.h    |  8 ++++
 lib/Analysis/LoopDependenceAnalysis.cpp       | 41 ++++++++++++++++---
 2 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/include/llvm/Analysis/LoopDependenceAnalysis.h b/include/llvm/Analysis/LoopDependenceAnalysis.h
index 236f79ae970..272e0bd4d36 100644
--- a/include/llvm/Analysis/LoopDependenceAnalysis.h
+++ b/include/llvm/Analysis/LoopDependenceAnalysis.h
@@ -20,6 +20,7 @@
 #ifndef LLVM_ANALYSIS_LOOP_DEPENDENCE_ANALYSIS_H
 #define LLVM_ANALYSIS_LOOP_DEPENDENCE_ANALYSIS_H
 
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Analysis/LoopPass.h"
@@ -67,6 +68,10 @@ class LoopDependenceAnalysis : public LoopPass {
   /// created. The third argument is set to the pair found or created.
   bool findOrInsertDependencePair(Value*, Value*, DependencePair*&);
 
+  /// getLoops - Collect all loops of the loop-nest L a given SCEV is variant
+  /// in.
+  void getLoops(const SCEV*, DenseSet<const Loop*>*) const;
+
   /// isLoopInvariant - True if a given SCEV is invariant in all loops of the
   /// loop-nest starting at the innermost loop L.
   bool isLoopInvariant(const SCEV*) const;
@@ -78,7 +83,10 @@ class LoopDependenceAnalysis : public LoopPass {
 
   /// TODO: doc
   bool isZIVPair(const SCEV*, const SCEV*) const;
+  bool isSIVPair(const SCEV*, const SCEV*) const;
   DependenceResult analyseZIV(const SCEV*, const SCEV*, Subscript*) const;
+  DependenceResult analyseSIV(const SCEV*, const SCEV*, Subscript*) const;
+  DependenceResult analyseMIV(const SCEV*, const SCEV*, Subscript*) const;
   DependenceResult analyseSubscript(const SCEV*, const SCEV*, Subscript*) const;
   DependenceResult analysePair(DependencePair*) const;
 
diff --git a/lib/Analysis/LoopDependenceAnalysis.cpp b/lib/Analysis/LoopDependenceAnalysis.cpp
index eb8ea0ebdb0..d37273c3728 100644
--- a/lib/Analysis/LoopDependenceAnalysis.cpp
+++ b/lib/Analysis/LoopDependenceAnalysis.cpp
@@ -20,6 +20,7 @@
 //===----------------------------------------------------------------------===//
 
 #define DEBUG_TYPE "lda"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/LoopDependenceAnalysis.h"
@@ -124,11 +125,18 @@ bool LoopDependenceAnalysis::findOrInsertDependencePair(Value *A,
   return false;
 }
 
-bool LoopDependenceAnalysis::isLoopInvariant(const SCEV *S) const {
+void LoopDependenceAnalysis::getLoops(const SCEV *S,
+                                      DenseSet<const Loop*>* Loops) const {
+  // Refactor this into an SCEVVisitor, if efficiency becomes a concern.
   for (const Loop *L = this->L; L != 0; L = L->getParentLoop())
     if (!S->isLoopInvariant(L))
-      return false;
-  return true;
+      Loops->insert(L);
+}
+
+bool LoopDependenceAnalysis::isLoopInvariant(const SCEV *S) const {
+  DenseSet<const Loop*> loops;
+  getLoops(S, &loops);
+  return loops.empty();
 }
 
 bool LoopDependenceAnalysis::isAffine(const SCEV *S) const {
@@ -140,6 +148,13 @@ bool LoopDependenceAnalysis::isZIVPair(const SCEV *A, const SCEV *B) const {
   return isLoopInvariant(A) && isLoopInvariant(B);
 }
 
+bool LoopDependenceAnalysis::isSIVPair(const SCEV *A, const SCEV *B) const {
+  DenseSet<const Loop*> loops;
+  getLoops(A, &loops);
+  getLoops(B, &loops);
+  return loops.size() == 1;
+}
+
 LoopDependenceAnalysis::DependenceResult
 LoopDependenceAnalysis::analyseZIV(const SCEV *A,
                                    const SCEV *B,
@@ -148,6 +163,20 @@ LoopDependenceAnalysis::analyseZIV(const SCEV *A,
   return A == B ? Dependent : Independent;
 }
 
+LoopDependenceAnalysis::DependenceResult
+LoopDependenceAnalysis::analyseSIV(const SCEV *A,
+                                   const SCEV *B,
+                                   Subscript *S) const {
+  return Unknown; // TODO: Implement.
+}
+
+LoopDependenceAnalysis::DependenceResult
+LoopDependenceAnalysis::analyseMIV(const SCEV *A,
+                                   const SCEV *B,
+                                   Subscript *S) const {
+  return Unknown; // TODO: Implement.
+}
+
 LoopDependenceAnalysis::DependenceResult
 LoopDependenceAnalysis::analyseSubscript(const SCEV *A,
                                          const SCEV *B,
@@ -167,10 +196,10 @@ LoopDependenceAnalysis::analyseSubscript(const SCEV *A,
   if (isZIVPair(A, B))
     return analyseZIV(A, B, S);
 
-  // TODO: Implement SIV/MIV testers.
+  if (isSIVPair(A, B))
+    return analyseSIV(A, B, S);
 
-  DEBUG(errs() << "  -> [?] cannot analyse subscript\n");
-  return Unknown;
+  return analyseMIV(A, B, S);
 }
 
 LoopDependenceAnalysis::DependenceResult