From fa151a79ed2d0efc8fe1d7378be264b301d8caf1 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Tue, 6 Sep 2011 05:05:14 +0000
Subject: The logic inside getMulExpr to simplify {a,+,b}*{c,+,d} was wrong,
 which was visible given a=b=c=d=1, on iteration #1 (the second iteration).
 Replace it with correct math. Fixes PR10383!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@139133 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolution.cpp | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

(limited to 'lib/Analysis/ScalarEvolution.cpp')

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 8859c3b..6d28f69 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -1735,7 +1735,7 @@ const SCEV *ScalarEvolution::getAddExpr(SmallVectorImpl<const SCEV *> &Ops,
       // If all of the other operands were loop invariant, we are done.
       if (Ops.size() == 1) return NewRec;
 
-      // Otherwise, add the folded AddRec by the non-liv parts.
+      // Otherwise, add the folded AddRec by the non-live parts.
       for (unsigned i = 0;; ++i)
         if (Ops[i] == AddRec) {
           Ops[i] = NewRec;
@@ -1960,7 +1960,7 @@ const SCEV *ScalarEvolution::getMulExpr(SmallVectorImpl<const SCEV *> &Ops,
       // If all of the other operands were loop invariant, we are done.
       if (Ops.size() == 1) return NewRec;
 
-      // Otherwise, multiply the folded AddRec by the non-liv parts.
+      // Otherwise, multiply the folded AddRec by the non-live parts.
       for (unsigned i = 0;; ++i)
         if (Ops[i] == AddRec) {
           Ops[i] = NewRec;
@@ -1976,22 +1976,29 @@ const SCEV *ScalarEvolution::getMulExpr(SmallVectorImpl<const SCEV *> &Ops,
          OtherIdx < Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]);
          ++OtherIdx)
       if (AddRecLoop == cast<SCEVAddRecExpr>(Ops[OtherIdx])->getLoop()) {
-        // F * G, where F = {A,+,B}<L> and G = {C,+,D}<L>  -->
-        // {A*C,+,F*D + G*B + B*D}<L>
+        // {A,+,B}<L> * {C,+,D}<L>  -->  {A*C,+,A*D + B*C + B*D,+,2*B*D}<L>
         for (; OtherIdx != Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]);
              ++OtherIdx)
           if (const SCEVAddRecExpr *OtherAddRec =
                 dyn_cast<SCEVAddRecExpr>(Ops[OtherIdx]))
             if (OtherAddRec->getLoop() == AddRecLoop) {
-              const SCEVAddRecExpr *F = AddRec, *G = OtherAddRec;
-              const SCEV *NewStart = getMulExpr(F->getStart(), G->getStart());
-              const SCEV *B = F->getStepRecurrence(*this);
-              const SCEV *D = G->getStepRecurrence(*this);
-              const SCEV *NewStep = getAddExpr(getMulExpr(F, D),
-                                               getMulExpr(G, B),
-                                               getMulExpr(B, D));
-              const SCEV *NewAddRec = getAddRecExpr(NewStart, NewStep,
-                                                    F->getLoop(),
+              const SCEV *A = AddRec->getStart();
+              const SCEV *B = AddRec->getStepRecurrence(*this);
+              const SCEV *C = OtherAddRec->getStart();
+              const SCEV *D = OtherAddRec->getStepRecurrence(*this);
+              const SCEV *NewStart = getMulExpr(A, C);
+              const SCEV *BD = getMulExpr(B, D);
+              const SCEV *NewStep = getAddExpr(getMulExpr(A, D),
+                                               getMulExpr(B, C), BD);
+              const SCEV *NewSecondOrderStep =
+                  getMulExpr(BD, getConstant(BD->getType(), 2));
+
+              SmallVector<const SCEV *, 3> AddRecOps;
+              AddRecOps.push_back(NewStart);
+              AddRecOps.push_back(NewStep);
+              AddRecOps.push_back(NewSecondOrderStep);
+              const SCEV *NewAddRec = getAddRecExpr(AddRecOps,
+                                                    AddRec->getLoop(),
                                                     SCEV::FlagAnyWrap);
               if (Ops.size() == 2) return NewAddRec;
               Ops[Idx] = AddRec = cast<SCEVAddRecExpr>(NewAddRec);
-- 
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