[llvm] r264051 - [PATCH] Force LoopReroll to reset the loop trip count value after reroll.

[Zinovy Nis via llvm-commits]

Author: zinovy.nis
Date: Tue Mar 22 08:50:57 2016
New Revision: 264051

URL: http://llvm.org/viewvc/llvm-project?rev=264051&view=rev
Log:
[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

Modified:
    llvm/trunk/lib/Transforms/Scalar/LoopRerollPass.cpp
    llvm/trunk/test/Transforms/LoopReroll/basic32iters.ll

Modified: llvm/trunk/lib/Transforms/Scalar/LoopRerollPass.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopRerollPass.cpp?rev=264051&r1=264050&r2=264051&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopRerollPass.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopRerollPass.cpp Tue Mar 22 08:50:57 2016
@@ -1551,14 +1551,12 @@ bool LoopReroll::runOnLoop(Loop *L, LPPa
         "] 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, LPPa
 
   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, LPPa
       break;
     }
 
+  // Trip count of L has changed so SE must be re-evaluated.
+  if (Changed)
+    SE->forgetLoop(L);
+
   return Changed;
 }

Modified: llvm/trunk/test/Transforms/LoopReroll/basic32iters.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopReroll/basic32iters.ll?rev=264051&r1=264050&r2=264051&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopReroll/basic32iters.ll (original)
+++ llvm/trunk/test/Transforms/LoopReroll/basic32iters.ll Tue Mar 22 08:50:57 2016
@@ -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"