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

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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

llvm-svn: 353017
This commit is contained in:
Max Kazantsev 2019-02-04 05:04:19 +00:00
parent 32f3ee2f37
commit ae64db0c14
2 changed files with 2 additions and 2 deletions
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2
lib/Analysis/ScalarEvolution.cpp
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@ -6144,7 +6144,7 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
// 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))

2
test/Analysis/ScalarEvolution/unreachable-code.ll
View File

@ -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: