[llvm] r353017 - [SCEV] Do not bother creating separate SCEVUnknown for unreachable nodes

[Max Kazantsev via llvm-commits]

Author: mkazantsev
Date: Sun Feb  3 21:04:19 2019
New Revision: 353017

URL: http://llvm.org/viewvc/llvm-project?rev=353017&view=rev
Log:
[SCEV] Do not bother creating separate SCEVUnknown for unreachable nodes

Currently, SCEV creates SCEVUnknown for every node of unreachable code. If we
have a huge amounts of such code, we will be littering SE with these nodes. We could
just state that they all are undef and save some memory.

Differential Revision: https://reviews.llvm.org/D57567
Reviewed By: sanjoy

Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp
    llvm/trunk/test/Analysis/ScalarEvolution/unreachable-code.ll

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=353017&r1=353016&r2=353017&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Sun Feb  3 21:04:19 2019
@@ -6144,7 +6144,7 @@ const SCEV *ScalarEvolution::createSCEV(
     // to obey basic rules for definitions dominating uses which this
     // analysis depends on.
     if (!DT.isReachableFromEntry(I->getParent()))
-      return getUnknown(V);
+      return getUnknown(UndefValue::get(V->getType()));
   } else if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
     return getConstant(CI);
   else if (isa<ConstantPointerNull>(V))

Modified: llvm/trunk/test/Analysis/ScalarEvolution/unreachable-code.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/unreachable-code.ll?rev=353017&r1=353016&r2=353017&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/unreachable-code.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/unreachable-code.ll Sun Feb  3 21:04:19 2019
@@ -1,7 +1,7 @@
 ; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
 
 ; CHECK: %t = add i64 %t, 1
-; CHECK: -->  %t
+; CHECK: -->  undef
 
 define void @foo() {
 entry: