[llvm-commits] [llvm-gcc][arm][patch] Lower function signatures a bit more

[Chris Lattner]

On Sep 9, 2010, at 2:34 PM, Rafael Espindola wrote:

>> I haven't reviewed the patch, but in principle this sounds like a great idea!
>> 
>> What IR does:
>>  double foo(double X, double Y) { return X+Y; }
>> 
>> get lowered into, and what ARM code ends up generated?
> 
> With the patch the generated IL is

Great, I was worried that the "long" IR wouldn't be pattern matched back into good machine code.  I think this is a great idea, doing it in clang would really be appreciated!

-Chris


> 
> ----------------------------------------------------------------------
> define double @foo(i32 %X.0, i32 %X.1, i32 %Y.0, i32 %Y.1) nounwind
> readnone optsize {
> entry:
>  %tmp17 = zext i32 %X.0 to i64
>  %tmp12 = zext i32 %X.1 to i64
>  %tmp13 = shl i64 %tmp12, 32
>  %ins15 = or i64 %tmp13, %tmp17
>  %tmp6 = zext i32 %Y.0 to i64
>  %tmp3 = zext i32 %Y.1 to i64
>  %tmp4 = shl i64 %tmp3, 32
>  %ins = or i64 %tmp4, %tmp6
>  %tmp10 = bitcast i64 %ins15 to double
>  %tmp2 = bitcast i64 %ins to double
>  %0 = fadd double %tmp10, %tmp2
>  ret double %0
> }
> ---------------------------------------------------------------------
> 
> and the asm is
> 
> ----------------------------------------------------------------
> foo:
> 	vmov	d0, r2, r3
> 	vmov	d1, r0, r1
> 	vadd.f64	d0, d1, d0
> 	vmov	r0, r1, d0
> 	bx	lr
> ----------------------------------------------------------------
> 
> or with -mfloat-abi=soft
> 
> -------------------------------------------------------------
> foo:
> 	stmdb	sp!, {r11, lr}
> 	bl	__adddf3
> 	ldmia	sp!, {r11, pc}
> -------------------------------------------------------------
> 
> Currently we get a more compact but less explicit IL:
> ----------------------------------------
> define double @foo(double %X, double %Y) nounwind readnone optsize {
> entry:
>  %0 = fadd double %X, %Y
>  ret double %0
> }
> ----------------------------------------
> 
> And exactly the same assembly.
> 
>> -Chris
> 
> 
> Cheers,
> -- 
> Rafael Ávila de Espíndola