forked from OSchip/llvm-project
0725a8b653
live case of a switch statement when switching on a constant. This is terribly
limited, but enough to handle the trivial example included. Before we would
emit:
define void @test1(i32 %i) nounwind {
entry:
%i.addr = alloca i32, align 4
store i32 %i, i32* %i.addr, align 4
switch i32 1, label %sw.epilog [
i32 1, label %sw.bb
]
sw.bb: ; preds = %entry
%tmp = load i32* %i.addr, align 4
%inc = add nsw i32 %tmp, 1
store i32 %inc, i32* %i.addr, align 4
br label %sw.epilog
sw.epilog: ; preds = %sw.bb, %entry
switch i32 0, label %sw.epilog3 [
i32 1, label %sw.bb1
]
sw.bb1: ; preds = %sw.epilog
%tmp2 = load i32* %i.addr, align 4
%add = add nsw i32 %tmp2, 2
store i32 %add, i32* %i.addr, align 4
br label %sw.epilog3
sw.epilog3: ; preds = %sw.bb1, %sw.epilog
ret void
}
now we emit:
define void @test1(i32 %i) nounwind {
entry:
%i.addr = alloca i32, align 4
store i32 %i, i32* %i.addr, align 4
%tmp = load i32* %i.addr, align 4
%inc = add nsw i32 %tmp, 1
store i32 %inc, i32* %i.addr, align 4
ret void
}
This improves -O0 compile time (less IR to generate and shove through the code
generator) and the clever linux kernel people found a way to fail to build if we
don't do this optimization. This step isn't enough to handle the kernel case
though.
llvm-svn: 126597
|
||
|---|---|---|
| .. | ||
| INPUTS | ||
| bindings/python | ||
| clang.xcodeproj | ||
| docs | ||
| examples | ||
| include | ||
| lib | ||
| runtime | ||
| test | ||
| tools | ||
| unittests | ||
| utils | ||
| www | ||
| CMakeLists.txt | ||
| INSTALL.txt | ||
| LICENSE.TXT | ||
| Makefile | ||
| ModuleInfo.txt | ||
| NOTES.txt | ||
| README.txt | ||
| TODO.txt | ||
README.txt
//===----------------------------------------------------------------------===// // C Language Family Front-end //===----------------------------------------------------------------------===// Welcome to Clang. This is a compiler front-end for the C family of languages (C, C++, Objective-C, and Objective-C++) which is built as part of the LLVM compiler infrastructure project. Unlike many other compiler frontends, Clang is useful for a number of things beyond just compiling code: we intend for Clang to be host to a number of different source level tools. One example of this is the Clang Static Analyzer. If you're interested in more (including how to build Clang) it is best to read the relevant web sites. Here are some pointers: Information on Clang: http://clang.llvm.org/ Building and using Clang: http://clang.llvm.org/get_started.html Clang Static Analyzer: http://clang-analyzer.llvm.org/ Information on the LLVM project: http://llvm.org/ If you have questions or comments about Clang, a great place to discuss them is on the Clang development mailing list: http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev If you find a bug in Clang, please file it in the LLVM bug tracker: http://llvm.org/bugs/