[LLVMdev] Auto-vectorization in GCC 4.0

[Devang Patel]

On Jul 31, 2006, at 11:14 AM, Vikram Adve wrote:

> Does llvmgcc4 convert the high-level AST to LLVM (like llvmgcc3x)  
> or does it go from GIMPL to LLVM?  If the latter, would it be  
> possible to allow some TreeSSA optimizations before emitting LLVM?

llvmgcc4 intercepts high-level GCC trees to GIMPLE tree  
transformation routines to get trees that are suitable for LLVM byte  
code. And TreeSSA optimizer may not be able to handle LLVM suitable  
GIMPLE trees. One such case is how Array references are handled (&a 
[i] vs a+i*size). However, I do not know exact details of LLVM byte  
code generation work inside llvmgcc4.

-
Devang

>
> --Vikram
> http://www.cs.uiuc.edu/~vadve
> http://llvm.cs.uiuc.edu/
>
>
> On Jul 31, 2006, at 1:10 PM, Devang Patel wrote:
>
>> llvmgcc4 emits LLVM byte code before executing GCC optimizations,  
>> so one can say that llvmgcc4 disables all GCC optimizations.
>>
>> On Jul 31, 2006, at 11:01 AM, Zhiru Zhang wrote:
>>
>>> Hi,
>>> I am trying to turn on the new GCC auto-vectorization feature  
>>> within llvmgcc4. Below is the command I used, but nothing was  
>>> vectorized. Does it mean that llvmgcc4 has disabled this  
>>> optimization and all I can do is to embed SSE intrinsics in the  
>>> source code by hand?
>>>
>>> Thanks!
>>>
>>> ./llvm-gcc4-x86/bin/llvm-gcc -c -O2 -ftree-vectorize -msse -ftree- 
>>> vectorizer-verbose=5 -emit-llvm vec.c -o vec.bc
>>>
>>> ////////////////////vec.c/////////////////////////
>>> int a[256], b[256], c[256];
>>> foo () {
>>>   int i;
>>>   for (i=0; i<256; i++){
>>>     a[i] = b[i] + c[i];
>>>   }
>>> }
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>> -
>> Devang
>>
>>
>>
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-
Devang