llvm dev - May 2007 - [LLVMdev] Question about the new version of LLVM GCC

I noticed the following line in the output of LLVM GCC and was
wondering what it meant:
   "alloca point" = bitcast i32 0 to i32   ; <i32> [#uses=0]
I wasn't aware that a string was a valid left hand side, but
considering the fact that the instruction is basically pointless
(doesn't do anything, and is never used), I'm guessing that it instead
serves to mark the end of the allocas for that function.  Is this
correct?  If not, what does the instruction mean/do?

Thanks,
Ben Chambers

On Sun, 20 May 2007, Ben Chambers wrote:
> I noticed the following line in the output of LLVM GCC and was
> wondering what it meant:
>   "alloca point" = bitcast i32 0 to i32   ; <i32> [#uses=0]
> I wasn't aware that a string was a valid left hand side, but
LLVM allows arbitrary characters to be in the names of values.  For simple 
things, it uses %foo, for complex things, it uses quoted strings (in this 
case, due to the space).
> considering the fact that the instruction is basically pointless
> (doesn't do anything, and is never used), I'm guessing that it
instead
> serves to mark the end of the allocas for that function.  Is this
> correct?  If not, what does the instruction mean/do?
The LLVM APIs make it easy, fast and convenient to insert an instruction 
before another one.  The llvm-gcc f.e. uses this bitcast as an anchor to 
insert (you guessed it) allocas.

-Chris

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