From e1d0fa1c2288e7141ee86c0c82093d75500ea144 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Sat, 7 Mar 2009 23:32:02 +0000 Subject: fix a serious pessimization that Tron on IRC pointed out where we would "boolify" pointers, generating really awful code because getting the pointer value requires a load itself. Before: _foo: movb $1, _X.b ret _get: xorl %ecx, %ecx movb _X.b, %al testb %al, %al movl $_Y, %eax cmove %ecx, %eax ret With the xform disabled: _foo: movl $_Y, _X ret _get: movl _X, %eax ret git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66351 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/IPO/GlobalOpt.cpp | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'lib/Transforms/IPO') diff --git a/lib/Transforms/IPO/GlobalOpt.cpp b/lib/Transforms/IPO/GlobalOpt.cpp index b93eb6b..1d0993a 100644 --- a/lib/Transforms/IPO/GlobalOpt.cpp +++ b/lib/Transforms/IPO/GlobalOpt.cpp @@ -1531,10 +1531,12 @@ static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) { const Type *GVElType = GV->getType()->getElementType(); // If GVElType is already i1, it is already shrunk. If the type of the GV is - // an FP value or vector, don't do this optimization because a select between - // them is very expensive and unlikely to lead to later simplification. + // an FP value, pointer or vector, don't do this optimization because a select + // between them is very expensive and unlikely to lead to later + // simplification. In these cases, we typically end up with "cond ? v1 : v2" + // where v1 and v2 both require constant pool loads, a big loss. if (GVElType == Type::Int1Ty || GVElType->isFloatingPoint() || - isa(GVElType)) + isa(GVElType) || isa(GVElType)) return false; // Walk the use list of the global seeing if all the uses are load or store. -- cgit v1.1