[PATCH] D57567: [SCEV] Do not bother creating separate SCEVUnknown for unreachable nodes

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added reviewers: sanjoy, skatkov.
Herald added a subscriber: javed.absar.

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 zero and save some memory.


https://reviews.llvm.org/D57567

Files:
  lib/Analysis/ScalarEvolution.cpp
  test/Analysis/ScalarEvolution/unreachable-code.ll


Index: test/Analysis/ScalarEvolution/unreachable-code.ll
===================================================================
--- test/Analysis/ScalarEvolution/unreachable-code.ll
+++ test/Analysis/ScalarEvolution/unreachable-code.ll
@@ -1,7 +1,7 @@
 ; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
 
 ; CHECK: %t = add i64 %t, 1
-; CHECK: -->  %t
+; CHECK: -->  0
 
 define void @foo() {
 entry:
Index: lib/Analysis/ScalarEvolution.cpp
===================================================================
--- lib/Analysis/ScalarEvolution.cpp
+++ lib/Analysis/ScalarEvolution.cpp
@@ -6144,7 +6144,7 @@
     // to obey basic rules for definitions dominating uses which this
     // analysis depends on.
     if (!DT.isReachableFromEntry(I->getParent()))
-      return getUnknown(V);
+      return getZero(V->getType());
   } else if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
     return getConstant(CI);
   else if (isa<ConstantPointerNull>(V))


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