From: Evan Cheng <evan.cheng@apple.com>
Date: Thu, 13 Dec 2007 03:32:53 +0000 (+0000)
Subject: Be extra careful with extension use optimation. Now turned on by default.
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=commitdiff_plain;h=f9785f92b630e69262c395b2fc0893451169d68b

Be extra careful with extension use optimation. Now turned on by default.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44981 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp
index 47e60cd74b4..8da09127e96 100644
--- a/lib/Transforms/Scalar/CodeGenPrepare.cpp
+++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp
@@ -36,7 +36,7 @@ using namespace llvm;
 
 namespace {
   cl::opt<bool> OptExtUses("optimize-ext-uses",
-                           cl::init(false), cl::Hidden);
+                           cl::init(true), cl::Hidden);
 }
 
 namespace {  
@@ -929,6 +929,10 @@ bool CodeGenPrepare::OptimizeExtUses(Instruction *I) {
   if (Src->hasOneUse())
     return false;
 
+  // Only do this xform is truncating is free.
+  if (!TLI->isTruncateFree(I->getType(), Src->getType()))
+    return false;
+
   // Only safe to perform the optimization if the source is also defined in
   // this block.
   if (!isa<Instruction>(Src) || DefBB != cast<Instruction>(Src)->getParent())
@@ -952,8 +956,11 @@ bool CodeGenPrepare::OptimizeExtUses(Instruction *I) {
   for (Value::use_iterator UI = Src->use_begin(), E = Src->use_end(); 
        UI != E; ++UI) {
     Instruction *User = cast<Instruction>(*UI);
-    if (User->getParent() == DefBB) continue;
-    if (isa<PHINode>(User))
+    BasicBlock *UserBB = User->getParent();
+    if (UserBB == DefBB) continue;
+    // Be conservative. We don't want this xform to end up introducing
+    // reloads just before load / store instructions.
+    if (isa<PHINode>(User) || isa<LoadInst>(User) || isa<StoreInst>(User))
       return false;
   }
 
diff --git a/test/CodeGen/X86/opt-ext-uses.ll b/test/CodeGen/X86/opt-ext-uses.ll
index faa9be75504..322850c5523 100644
--- a/test/CodeGen/X86/opt-ext-uses.ll
+++ b/test/CodeGen/X86/opt-ext-uses.ll
@@ -1,4 +1,4 @@
-; RUN: llvm-as < %s | llc -march=x86 -optimize-ext-uses=true | grep movw | count 1
+; RUN: llvm-as < %s | llc -march=x86 | grep movw | count 1
 
 define i16 @t() signext  {
 entry: