llvm dev - Nov 2006 - [LLVMdev] Byte code portability (was Re: libstdc++ as bytecode, and compiling C++ to C)

Reid Spencer schrieb:
> Hi Philipp,
> 
> On Fri, 2006-11-24 at 20:09 +0100, Philipp Klaus Krause wrote:
>> Reid Spencer schrieb:
>>
>>> Note that C and LLVM types are *not* the same things (despite the
>>> similar names). We are in the process of making this abundantly
clear.
>>> The LLVM IR will soon use names like i8, i16, i32, and i64
(signless
>>> integer quantities of specific sizes, regardless of platform).
>> I had explicitly specified the size in the input code using a uint32_t
>> type, the resulting C code used short, which is smaller on my target
>> platform.
> 
> One would think that it should result in a 32-bit unsigned type but its
> hard to say without something concrete. Can you supply a small,
> pre-processed example of some code that results in a CBE short for an
> input C/C++ uint32_t ?
Hmm the problem was a bit different. I just reproduced it.

I used this input file:

#include <stdint.h>

uint32_t test(uint32_t t)
{
	return(t + 42);
}

and got the following code:

unsigned test(unsigned ltmp_0_1) {
  return (ltmp_0_1 + 42u);
}

unsigned is 16 bit on my target platform.

Philipp

On Fri, 2006-11-24 at 21:13 +0100, Philipp Klaus Krause
wrote:
> Reid Spencer schrieb:
> Hmm the problem was a bit different. I just reproduced it.
> 
> I used this input file:
> 
> #include <stdint.h>
> 
> uint32_t test(uint32_t t)
> {
> 	return(t + 42);
> }
> 
> and got the following code:
> 
> unsigned test(unsigned ltmp_0_1) {
>   return (ltmp_0_1 + 42u);
> }
> 
> unsigned is 16 bit on my target platform.
Sure, but what is it on the target that llvm-gcc is configured for? If
you're running llvm-gcc on a 32-bit platform without configuring it as a
cross-compiler then the above is correct. 32-bit unsigned is what is
expected on the target you're compiling for. This is exactly why its
important to configure llvm-gcc as a cross-compiler for your target. If
you do, I'm sure that you'll find it will generate:

unsigned long test (unsigned long ltmp_0_1) {
  return (ltmp_0_1 + 42ul);
}

assuming that "unsigned long" is a 32-bit unsigned long on your
target.

Reid.
> 
> Philipp
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On Fri, 24 Nov 2006, Reid Spencer wrote:
>>   return (ltmp_0_1 + 42u);
>> }
>>
>> unsigned is 16 bit on my target platform.
>
> Sure, but what is it on the target that llvm-gcc is configured for? If
> you're running llvm-gcc on a 32-bit platform without configuring it as
a
This has nothing to do with cross compiling.  The CBE always assumes that 
unsigned is 32-bits.  This is obviously false.  It should emit uint32_t 
references instead, but this requires pulling in <inttypes.h>, which it 
can't do.

-Chris

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