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

[Matthew Simpson via llvm-commits]

mssimpso updated this revision to Diff 32726.
mssimpso added a subscriber: jingyue.
mssimpso added a comment.

@jingyue:

Thanks for the correction. I've updated the comment.

@vaivaswatha:

Thanks for pointing me to http://reviews.llvm.org/D11771. I was curious to know if your change would
prevent the attached test case from aborting, but it did not. This test case is
reduced from a benchmark in spec2006, and we just need to check that it doesn't
abort. I'm not sure it would be very meaningful to translate it back into the
source language. Other DependenceAnalysis tests (e.g., Constraints.ll,
Invariant.ll) seem to do the same.


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 +1,36 @@
+; REQUIRES: asserts
+; RUN: opt < %s -analyze -basicaa -da-delinearize -da
+;
+; This is a reduced test case from a benchmark in spec2006. We check that this
+; code does not abort.
+;
+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(i32** %a, i32 %n) align 2 {
+for.preheader:
+  %t.0 = ashr exact i32 %n, 3
+  br label %for.body.1
+
+for.body.1:
+  %i.1 = phi i32 [ %t.5, %for.inc ], [ 0, %for.preheader ]
+  %i.2 = phi i32 [ %i.5, %for.inc ], [ %t.0, %for.preheader ]
+  br i1 undef, label %for.inc, label %for.body.2
+
+for.body.2:
+  %i.3 = phi i32 [ %t.1, %for.body.2 ], [ %i.1, %for.body.1 ]
+  %t.1 = add i32 %i.3, 1
+  %t.2 = load i32*, i32** %a, align 4
+  %t.3 = getelementptr inbounds i32, i32* %t.2, i32 %i.3
+  %t.4 = load i32, i32* %t.3, align 4
+  br i1 undef, label %for.inc, label %for.body.2
+
+for.inc:
+  %i.4 = phi i32 [ %i.2, %for.body.1 ], [ %i.2, %for.body.2 ]
+  %t.5 = add i32 %i.1, %i.4
+  %i.5 = add i32 %i.2, -1
+  br i1 undef, label %for.exit, label %for.body.1
+
+for.exit:
+  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");
 }
 
+/// Check that 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
@@ -3278,7 +3300,7 @@
 
   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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