On Mon, Dec 12, 2011 at 2:48 PM, BELBACHIR Selim <selim.belbac...@fr.thalesgroup.com> wrote: > Everything seems good when I use a union instead of "*((int *)(&af))". > > But I think that "*((int *)(&af))" is a valid syntax to get the integer > representation of my floating point value (in my test case 0x3F800000 for > 1.0f in IEEE-754). It may be target dependant but I think it should work on > target having 32 bits float and integer (and IEEE754 compliance).
It's valid syntax but invoking undefined behavior. You can use -fno-strict-aliasing to make behavior defined (or use a union). Richard. > I have gone on my debugging and I found what was wrong in my backend. I had > STACK_POINTER_REGNUM=$C0, ARG_POINTER_REGNUM=$C1, FRAME_POINTER_REGNUM=$C0, > no reg elimination macro, and prolog/epilog in adequacy. When I replaced my > FRAME_POINTER_REGNUM by its own $C2 reg (i.e. a different value than > STACK_POINTER_REGNUM) and added reg elimination macros the problem in dse2 > pass disappeared (without adding unnecessary frame pointer in the asm output). > I have done this because looking as dse2.c I saw that some optimization was > dealing with frame pointer and I was unsure of the correctness of the macro > defining my ABI. > > Are there requirement in dse2 pass according to FRAME_POINTER_REGNUM and > STACK_POINTER_REGNUM definition ? Does my initial definition of > FRAME_POINTER_REGNUM was totally dumb ? I don't know ... > > Selim > > > -----Message d'origine----- > De : gcc-ow...@gcc.gnu.org [mailto:gcc-ow...@gcc.gnu.org] De la part de > Andrew Haley > Envoyé : vendredi 9 décembre 2011 18:37 > À : gcc@gcc.gnu.org > Objet : Re: dse2 remove wrong insn > > On 12/09/2011 03:05 PM, BELBACHIR Selim wrote: >> int main() { >> int x; >> float af; >> ff(&x); >> af = f2(1.0f); >> return *((int *)(&af)); >> } > > Please try this again, but with a union rather than a pointer > cast. I don't think this code is legal C. > > Andrew.
