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

llvm-svn: 44981
This commit is contained in:
Evan Cheng 2007-12-13 03:32:53 +00:00
parent 23ffde507f
commit 37c36ed79a
2 changed files with 11 additions and 4 deletions
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13
llvm/lib/Transforms/Scalar/CodeGenPrepare.cpp
View File

@ -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;
}

2
llvm/test/CodeGen/X86/opt-ext-uses.ll
View File

@ -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: