[PATCH] D11725: [DependenceAnalysis] Ensure All Recurrences are Affine

[Matthew Simpson]

mssimpso created this revision.
mssimpso added reviewers: sebpop, grosser.
mssimpso added a subscriber: llvm-commits.

This patch ensures that all SCEVAddRecExprs in a SCEV expression
are affine before we attempt delinearization. The previous behavior
was to only consider the outer SCEVAddRecExpr without looking for
nested expressions.

http://reviews.llvm.org/D11725

Files:
  lib/Analysis/DependenceAnalysis.cpp
  test/Analysis/DependenceAnalysis/AffineSCEVAddRecExpr.ll

Index: test/Analysis/DependenceAnalysis/AffineSCEVAddRecExpr.ll
===================================================================
--- /dev/null
+++ test/Analysis/DependenceAnalysis/AffineSCEVAddRecExpr.ll
@@ -0,0 +1,45 @@
+; REQUIRES: asserts
+; RUN: opt -analyze -basicaa -da-delinearize -da %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n8:16:32-S64"
+target triple = "thumbv7--linux-gnueabi"
+
+define void @f() align 2 {
+entry:
+  %sub.ptr.div.i = ashr exact i32 undef, 3
+  br i1 undef, label %for.cond6.preheader.lr.ph, label %for.end56
+
+for.cond6.preheader.lr.ph:
+  br i1 undef, label %for.cond16.preheader, label %for.inc54
+
+for.cond16.preheader:
+  br i1 undef, label %for.inc48, label %for.cond19.preheader
+
+for.cond19.preheader:
+  %k.197 = phi i32 [ %2, %for.inc45 ], [ 0, %for.cond16.preheader ]
+  %indvars.iv8095 = phi i32 [ %indvars.iv.next81, %for.inc45 ], [ %sub.ptr.div.i, %for.cond16.preheader ]
+  br i1 undef, label %for.inc45, label %for.body23
+
+for.body23:
+  %k.292 = phi i32 [ %inc, %for.body23 ], [ %k.197, %for.cond19.preheader ]
+  %inc = add i32 %k.292, 1
+  %0 = load i32*, i32** undef, align 4
+  %add.ptr.i75 = getelementptr inbounds i32, i32* %0, i32 %k.292
+  %1 = load i32, i32* %add.ptr.i75, align 4
+  br i1 false, label %for.inc45, label %for.body23
+
+for.inc45:
+  %indvars.iv8096 = phi i32 [ %indvars.iv8095, %for.cond19.preheader ], [ %indvars.iv8095, %for.body23 ]
+  %2 = add i32 %k.197, %indvars.iv8096
+  %indvars.iv.next81 = add i32 %indvars.iv8095, -1
+  br i1 undef, label %for.inc48, label %for.cond19.preheader
+
+for.inc48:
+  unreachable
+
+for.inc54:
+  unreachable
+
+for.end56:
+  ret void
+}
Index: lib/Analysis/DependenceAnalysis.cpp
===================================================================
--- lib/Analysis/DependenceAnalysis.cpp
+++ lib/Analysis/DependenceAnalysis.cpp
@@ -3241,6 +3241,28 @@
     llvm_unreachable("constraint has unexpected kind");
 }
 
+/// Ensure all recurrences in an expression are affine.
+static bool allAddRecsAffine(const SCEVAddRecExpr *S) {
+
+  // Local struct for the SCEVTraversal. Traverse the expression until a
+  // SCEVAddRecExpr is found that is not affine.
+  struct AllAddRecsAffine {
+    bool IsAffine;
+    AllAddRecsAffine() : IsAffine(true) {}
+    bool follow(const SCEV *S) {
+      if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(S))
+        IsAffine = AddRec->isAffine();
+      return true;
+    }
+    bool isDone() { return !IsAffine; }
+  };
+
+  AllAddRecsAffine Check;
+  SCEVTraversal<AllAddRecsAffine> ST(Check);
+  ST.visitAll(S);
+  return Check.IsAffine;
+}
+
 /// Check if we can delinearize the subscripts. If the SCEVs representing the
 /// source and destination array references are recurrences on a nested loop,
 /// this function flattens the nested recurrences into separate recurrences
@@ -3262,7 +3284,7 @@
 
   const SCEVAddRecExpr *SrcAR = dyn_cast<SCEVAddRecExpr>(SrcSCEV);
   const SCEVAddRecExpr *DstAR = dyn_cast<SCEVAddRecExpr>(DstSCEV);
-  if (!SrcAR || !DstAR || !SrcAR->isAffine() || !DstAR->isAffine())
+  if (!SrcAR || !DstAR || !allAddRecsAffine(SrcAR) || !allAddRecsAffine(DstAR))
     return false;
 
   // First step: collect parametric terms in both array references.


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