From 6f6923fd4fdab46c88503c71548e076dd7373b74 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Sat, 7 Mar 2009 23:32:02 +0000 Subject: [PATCH] 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 +++++--- .../GlobalOpt/2009-03-07-PromotePtrToBool.ll | 17 +++++++++++++++++ 2 files changed, 22 insertions(+), 3 deletions(-) create mode 100644 test/Transforms/GlobalOpt/2009-03-07-PromotePtrToBool.ll diff --git a/lib/Transforms/IPO/GlobalOpt.cpp b/lib/Transforms/IPO/GlobalOpt.cpp index b93eb6b6d40..1d0993a7616 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. diff --git a/test/Transforms/GlobalOpt/2009-03-07-PromotePtrToBool.ll b/test/Transforms/GlobalOpt/2009-03-07-PromotePtrToBool.ll new file mode 100644 index 00000000000..8dba5b1c213 --- /dev/null +++ b/test/Transforms/GlobalOpt/2009-03-07-PromotePtrToBool.ll @@ -0,0 +1,17 @@ +; RUN: llvm-as < %s | opt -globalopt | llvm-dis | grep {@X = internal global i32} +target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128" +target triple = "i386-apple-darwin7" +@X = internal global i32* null ; [#uses=2] +@Y = internal global i32 0 ; [#uses=1] + +define void @foo() nounwind { +entry: + store i32* @Y, i32** @X, align 4 + ret void +} + +define i32* @get() nounwind { +entry: + %0 = load i32** @X, align 4 ; [#uses=1] + ret i32* %0 +} -- 2.34.1