Hi Amruta, When in doubt fire up gdb , put a breakpoint on gen_divmodsi3 (gen_<pattenrname>) and then you can find it from a backtrace 1 to find that out quickly. Anyways this would be from expand_divmod -> expand_twoval_binop -> the actual function from the backend. HTH cheers Raman On Sat, 2006-03-18 at 14:25 +0530, Amruta G. Gokhale wrote: > Hi Ramana, > > Thanks for your prompt reply. > > Yes, I am looking at the code produced using i386.md file. And yes, there > is a "divmod" pattern in i386.md file which, as you said, has led to > generation of this single INSN. > > But it would be great if you can let me know, which function or file in > GCC source code is involved in producing this single INSN. I have been > trying to trace out GCC source code for this, but with little success. > > Regards, > Amruta > > > On Sat, 18 Mar 2006, Ramana Radhakrishnan wrote: > > > Hi Amruta, > > > > I presume you are looking at the i386 backend. It can't be combine. > > Combine comes into the picture much much later than the initial > > expansion rounds. There are a set of named patterns that need to be > > supported in the backend and if the named patterns can be found, gcc > > expands using the named patterns. > > > > Look at the expander pattern for divmodsi4 .That creates this particular > > pattern and can be used for cases like the x86 where a single > > instruction can create both the quotient and the remainder. > > > >> From info gccint . (Read M as the machine mode :) ) > > > > > > `divmodM4' > > Signed division that produces both a quotient and a remainder. > > Operand 1 is divided by operand 2 to produce a quotient stored in > > operand 0 and a remainder stored in operand 3. > > > > For machines with an instruction that produces both a quotient and > > a remainder, provide a pattern for `divmodM4' but do not provide > > patterns for `divM3' and `modM3'. This allows optimization in the > > relatively common case when both the quotient and remainder are > > computed. > > > > If an instruction that just produces a quotient or just a remainder > > exists and is more efficient than the instruction that produces > > both, write the output routine of `divmodM4' to call > > `find_reg_note' and look for a `REG_UNUSED' note on the quotient > > or remainder and generate the appropriate instruction. > > > > HTH > > > > cheers > > Ramana > > > > On Sat, 2006-03-18 at 12:22 +0530, Amruta G. Gokhale wrote: > >> Hi, > >> > >> I am looking at some part of GCC source code which does the translation > >> from GIMPLE to RTL. > >> I created an example, having two consecutive instructions, one with "div" > >> and other with "mod". > >> > >> Example: > >> int a, b, c, d; > >> a = b / c; > >> d = b % c; > >> > >> The first-cut RTL code corresponding to these two instructions is a > >> PARALLEL INSN, with two SET INSNs, one with "div" and other with "mod". > >> (insn 22 21 23 1 (parallel [ > >> (set (reg:SI 70) > >> (div:SI (reg:SI 72) > >> (mem/i:SI (plus:SI (reg/f:SI 54 virtual-stack-vars) > >> (const_int -8 [0xfffffff8])) [0 c+0 S4 A32]))) > >> (set (reg:SI 71) > >> (mod:SI (reg:SI 72) > >> (mem/i:SI (plus:SI (reg/f:SI 54 virtual-stack-vars) > >> (const_int -8 [0xfffffff8])) [0 c+0 S4 A32]))) > >> ) > >> > >> I am unable to understand how a single INSN gets generated for these two > >> instructions. The GIMPLE code has two different tree nodes for the two > >> instructions, namely "trunc_div_expr" and "trunc_mod_expr". So there > >> should be two different INSNs. My guess is, some pass, like "combine", > >> must be combining two INSNs into one. > >> I looked at functions in file "combine.c", but no function in that file is > >> called! > >> > >> Can anybody suggest something? I am really stuck at this point And can't > >> proceed any further. > >> > >> Regards, > >> > >> Amruta Gokhale > >> Graduate Student > >> IIT Bombay, > >> Mumbai. > > > >
