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digitalmars.D - GDC and leaf functions

reply Manu <turkeyman gmail.com> writes:
I'm doing a lot of experiments with GDC, and I'm noticing that leaf
functions are still generating a stack frame and doing pointless work...

int leaf() pure nothrow
{
  return 0;
}

compile with -frelease -finline -O3, etc

I expect 2 opcodes, load immediate and return, but I get a whole pointless
function including memory access O_O

Any ideas? Is this normal?
Mar 04 2013
parent reply "David Nadlinger" <see klickverbot.at> writes:
On Monday, 4 March 2013 at 15:25:43 UTC, Manu wrote:
 I'm doing a lot of experiments with GDC, and I'm noticing that 
 leaf
 functions are still generating a stack frame and doing 
 pointless work...

 int leaf() pure nothrow
 {
   return 0;
 }

 compile with -frelease -finline -O3, etc

 I expect 2 opcodes, load immediate and return, but I get a 
 whole pointless
 function including memory access O_O

 Any ideas? Is this normal?

http://d.godbolt.org/#%7B%22version%22%3A3%2C%22filterAsm%22%3A%7B%22labels%22%3Atrue%2C%22directives%22%3Atrue%2C%22commentOnly%22%3Atrue%2C%22intel%22%3Atrue%7D%2C%22compilers%22%3A%5B%7B%22source%22%3A%22int%20leaf()%20pure%20nothrow%5Cn%7B%5Cn%20%20return%200%3B%5Cn%7D%22%2C%22compiler%22%3A%22%2Fusr%2Fbin%2Fgdc%22%2C%22options%22%3A%22-O3%20-march%3Dnative%22%7D%5D%7D The rest is just code for registering the ModuleInfo of the given module in the global list. David
Mar 04 2013
parent Manu <turkeyman gmail.com> writes:
Hmm, it seems PPC is working too.
Actually, maybe it's just SH4. I think my tests on other arch's were thrown
by bad compiler options.
Hmmm...

extern(C) float testfunc(float v, float v2)
{
return v*v2 + v2;
}


PPC:

testfunc:
fmadds 1,1,2,2
blr


MIPS:

testfunc:
j $31
madd.s $f0,$f13,$f12,$f13



SH4 Produces:

testfunc:
mov.l .L3,r1
lds.l  r1+,fpscr
add #-4,r1
fmov fr4,fr0
add #4,r1
fmac fr0,fr5,fr0
rts
lds.l  r1+,fpscr


But it should be:

testfunc:
fmov fr4,fr0
fmac fr0,fr5,fr0
rts



On 5 March 2013 03:39, David Nadlinger <see klickverbot.at> wrote:

 On Monday, 4 March 2013 at 15:25:43 UTC, Manu wrote:

 I'm doing a lot of experiments with GDC, and I'm noticing that leaf
 functions are still generating a stack frame and doing pointless work...

 int leaf() pure nothrow
 {
   return 0;
 }

 compile with -frelease -finline -O3, etc

 I expect 2 opcodes, load immediate and return, but I get a whole pointle=


ss
 function including memory access O_O

 Any ideas? Is this normal?

http://d.godbolt.org/#%7B%**22version%22%3A3%2C%** 22filterAsm%22%3A%7B%22labels%**22%3Atrue%2C%22directives%22%** 3Atrue%2C%22commentOnly%22%**3Atrue%2C%22intel%22%3Atrue%** 7D%2C%22compilers%22%3A%5B%7B%**22source%22%3A%22int%20leaf()%** 20pure%20nothrow%5Cn%7B%5Cn%**20%20return%200%3B%5Cn%7D%22%** 2C%22compiler%22%3A%22%2Fusr%**2Fbin%2Fgdc%22%2C%22options%** 22%3A%22-O3%20-march%3Dnative%**22%7D%5D%7D<http://d.godbolt.org/#%7B%22v=

ersion%22%3A3%2C%22filterAsm%22%3A%7B%22labels%22%3Atrue%2C%22directives%22= %3Atrue%2C%22commentOnly%22%3Atrue%2C%22intel%22%3Atrue%7D%2C%22compilers%2= 2%3A%5B%7B%22source%22%3A%22int%20leaf()%20pure%20nothrow%5Cn%7B%5Cn%20%20r= eturn%200%3B%5Cn%7D%22%2C%22compiler%22%3A%22%2Fusr%2Fbin%2Fgdc%22%2C%22opt= ions%22%3A%22-O3%20-march%3Dnative%22%7D%5D%7D>
 The rest is just code for registering the ModuleInfo of the given module
 in the global list.

 David

Mar 04 2013