From: Bob Wilson <bob.wilson@apple.com>
Date: Tue, 2 Mar 2010 00:09:29 +0000 (+0000)
Subject: Don't attempt load PRE when there is no real redundancy (i.e., the load is in
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=3bd19d753baf13577a43e0375bd7283379ad914a;p=oota-llvm.git

Don't attempt load PRE when there is no real redundancy (i.e., the load is in
a loop and is itself the only dependency).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97526 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index a4c07160249..fcb802a72ae 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -1542,11 +1542,13 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
   // at least one of the values is LI.  Since this means that we won't be able
   // to eliminate LI even if we insert uses in the other predecessors, we will
   // end up increasing code size.  Reject this by scanning for LI.
-  if (!EnableFullLoadPRE) {
-    for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
-      if (ValuesPerBlock[i].isSimpleValue() &&
-          ValuesPerBlock[i].getSimpleValue() == LI)
+  for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
+    if (ValuesPerBlock[i].isSimpleValue() &&
+        ValuesPerBlock[i].getSimpleValue() == LI) {
+      // Skip cases where LI is the only definition, even for EnableFullLoadPRE.
+      if (!EnableFullLoadPRE || e == 1)
         return false;
+    }
   }
 
   // FIXME: It is extremely unclear what this loop is doing, other than