From 07ac2bd4d0ed3dfd9b93e49ba302f7197bc0cd6d Mon Sep 17 00:00:00 2001
From: Zinovy Nis <zinovy.nis@gmail.com>
Date: Tue, 22 Mar 2016 13:50:57 +0000
Subject: [PATCH] [PATCH] Force LoopReroll to reset the loop trip count value
 after reroll.

It's a bug fix.
For rerolled loops SE trip count remains unchanged. It leads to incorrect work of the next passes.
My patch just resets SE info for rerolled loop forcing SE to re-evaluate it next time it requested.
I also added a verifier call in the exisitng test to be sure no invalid SE data remain. Without my fix this test would fail with -verify-scev.

Differential Revision: http://reviews.llvm.org/D18316

llvm-svn: 264051
---
 llvm/lib/Transforms/Scalar/LoopRerollPass.cpp   | 13 ++++++++-----
 llvm/test/Transforms/LoopReroll/basic32iters.ll |  2 +-
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp b/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp
index fae80d90ea70..3fb0a104c3fd 100644
--- a/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRerollPass.cpp
@@ -1551,14 +1551,12 @@ bool LoopReroll::runOnLoop(Loop *L, LPPassManager &LPM) {
         "] Loop %" << Header->getName() << " (" <<
         L->getNumBlocks() << " block(s))\n");
 
-  bool Changed = false;
-
   // For now, we'll handle only single BB loops.
   if (L->getNumBlocks() > 1)
-    return Changed;
+    return false;
 
   if (!SE->hasLoopInvariantBackedgeTakenCount(L))
-    return Changed;
+    return false;
 
   const SCEV *LIBETC = SE->getBackedgeTakenCount(L);
   const SCEV *IterCount = SE->getAddExpr(LIBETC, SE->getOne(LIBETC->getType()));
@@ -1572,11 +1570,12 @@ bool LoopReroll::runOnLoop(Loop *L, LPPassManager &LPM) {
 
   if (PossibleIVs.empty()) {
     DEBUG(dbgs() << "LRR: No possible IVs found\n");
-    return Changed;
+    return false;
   }
 
   ReductionTracker Reductions;
   collectPossibleReductions(L, Reductions);
+  bool Changed = false;
 
   // For each possible IV, collect the associated possible set of 'root' nodes
   // (i+1, i+2, etc.).
@@ -1587,5 +1586,9 @@ bool LoopReroll::runOnLoop(Loop *L, LPPassManager &LPM) {
       break;
     }
 
+  // Trip count of L has changed so SE must be re-evaluated.
+  if (Changed)
+    SE->forgetLoop(L);
+
   return Changed;
 }
diff --git a/llvm/test/Transforms/LoopReroll/basic32iters.ll b/llvm/test/Transforms/LoopReroll/basic32iters.ll
index d39b0e6a9157..758fd8a0a790 100644
--- a/llvm/test/Transforms/LoopReroll/basic32iters.ll
+++ b/llvm/test/Transforms/LoopReroll/basic32iters.ll
@@ -1,4 +1,4 @@
-; RUN: opt < %s -loop-reroll -S | FileCheck %s
+; RUN: opt < %s -loop-reroll -verify-scev -S | FileCheck %s
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"