Updated LLVM+GCC Patch

[Chris Lattner]

Hi Everyone,

Here is an updated version of the LLVM/GCC integration patch I've  
been working on.  Relative to the last patch, this one features:

1. Better support for many builtins, including builtin returnaddress,  
frameaddress, prefetch, stacksave/restore, memcpy, etc.
2. Structure layout is now *right*, including bitfield layout and  
variable sized member in structures.  This fixes the previous  
bitfield layout issues and implements static global initialization of  
bitfields/VLAs.
3. stacksave/restore have been implemented in LLVM and its code  
generators for full (backend) C99 VLA support.
4. "int A[2]; int*B = &A[1];" works.
5. This adds a new -emit-llvm option to the compiler, causing an LLVM  
".ll" file to be emitted to the .s file instead of native machine  
code, the first step to supporting link-time optimization/codegen.   
This only is useful when combined with -S right now, as the driver  
still invokes the native assembler, which obviously doesn't grok LLVM  
assembly.
6. This adds support for file-scope inline asm blocks, but no other  
inline asm yet.

Finally this fixes a small collection of other random bugs, including  
a dangling pointer problem in the type layout code and several  
bitfield accessing issues.

This compiler works quite well for me, building large code bases and  
passing the LLVM test-suite (except for C++ EH).  When I have some of  
the features below implemented I will start running the GCC test-suite.

So, now that the basics are here, what is missing? The major missing  
pieces are:

1. No debug support.  This doesn't even have line number support  
yet.  LLVM debug support as a whole is improving by leaps and bounds,  
so this will probably not be far off now.
2. ASM_EXPR is rejected.  My current task is to implement the rest of  
inline asm support in LLVM.  Doing so will also fix some of the ugly  
parts of this patch that #ifdef out inline asm code.
3. Dwarf exception handling isn't supported by the LLVM code  
generator, and isn't emitted by the front-end yet.  This will be my  
task immediately after #2 is done, at which point I'll complete the  
implementation of C++ exception throwing/catching.
4. Vector support is still very basic.  Generic vector support seems  
to work well, but no target intrinsics are passed through yet.  This  
part will be picked up by other people unless I finish #2/#3 first.

I have only tested this work on PowerPC/darwin with C/objc/c++, so  
I'd be happy to have others try it out and report problems to me.   
Here are the basic instructions for using this:

1. Decide whether you want a checking-enabled compiler or not.   
Checking slows down compiles substantially, but is useful for debugging.
2. Get LLVM CVS and build it 'make tools-only' for a checking build,  
'make tools-only ENABLE_OPTIMIZED=1' for a non-checking build.
3. Download this GCC SVN branch "svn://gcc.gnu.org/svn/gcc/branches/ 
apple/trunk/gcc", revision 108127.
4. Configure GCC SVN with "--enable-languages=c,objc,c++ --enable- 
llvm=<llvmobjroot>" and with "--enable-checking" if you want a  
checking enabled build.  Also specify "--prefix=...", "--program- 
prefix=llvm-" or any other arguments you want.
5. I use 'make; make install' to get a working tree.

At this point you should have an LLVM-enabled GCC.  As a simple  
"demo", you should be able to do this (to tell that it is llvm enabled):

------
$ <prefix>/bin/gcc -v
...
gcc version 4.0.1 LLVM (Apple Computer, Inc. build 5400)
$ echo 'int main() { puts("hello world"); }' > test.c
$ <prefix>/bin/gcc test.c -O
$ ./a.out
hello world
$ <prefix>/bin/gcc test.c -emit-llvm -O -S -o -
; ModuleID = 'test.c'
target endian = big
target pointersize = 32
target triple = "powerpc-apple-darwin8.2.0"
%str = internal constant [12 x sbyte] c"hello world\00"         ; < 
[12 x sbyte]*> [#uses=1]

implementation   ; Functions:

int %main() {
entry:
         %tmp = call int %puts( sbyte* getelementptr ([12 x sbyte]* % 
str, int 0, uint 0) )          ; <int> [#uses=0]
         ret int undef
}

declare int %puts(sbyte*)
------

As mentioned, my testing has been thorough on PPC/darwin, but I  
haven't tried any other target.  I'd be happy to get reports of how  
well things work on other targets, and any other bugs people run  
into.  Note that this all currently uses the native LLVM code  
generators, so it will only support targets that LLVM natively  
supports.  Further, gcc/Makefile.in (see LLVMTARGETOBJCMD) currently  
only knows about X86 and PowerPC, so basically the only other targets  
it makes sense to try right now is linux/i386.

When I'm done with inline asm and dwarf exceptions, I will start  
getting this reviewed and trying to push bits and pieces of this into  
the (apple) GCC tree.

-Chris

http://llvm.org/
http://nondot.org/sabre/


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