From: Sanjoy Das <sanjoy@playingwithpointers.com>
Date: Wed, 26 Jul 2017 01:32:19 +0000 (+0000)
Subject: [SCEV] Remove unnecessary call to forgetMemoizedResults
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=69b28c878234ed98456c7f6f4d386c3b4826ae0c;p=llvm

[SCEV] Remove unnecessary call to forgetMemoizedResults

`SCEVUnknown::allUsesReplacedWith` does not need to call `forgetMemoizedResults`
since RAUW does a value-equivalent replacement by assumption.  If this
assumption was false then the later setValPtr(New) call would be incorrect too.

This is a non-trivial performance optimization for functions with a large number
of loops since `forgetMemoizedResults` walks all loop backedge taken counts to
see if any of them use the SCEVUnknown being RAUWed.  However, this improvement
is difficult to demonstrate without checking in an excessively large IR file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309072 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index b726fd97b70..4d7b59c4763 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -415,9 +415,6 @@ void SCEVUnknown::deleted() {
 }
 
 void SCEVUnknown::allUsesReplacedWith(Value *New) {
-  // Clear this SCEVUnknown from various maps.
-  SE->forgetMemoizedResults(this);
-
   // Remove this SCEVUnknown from the uniquing map.
   SE->UniqueSCEVs.RemoveNode(this);