2014-02-14 15:40 GMT+01:00 Uros Bizjak <ubiz...@gmail.com>: > On Fri, Feb 14, 2014 at 2:48 PM, Kai Tietz <ktiet...@googlemail.com> wrote: >> 2014-02-14 13:55 GMT+01:00 Uros Bizjak <ubiz...@gmail.com>: >>> Hello! >>> >>>> 2014-02-14 Kai Tietz <kti...@redhat.com> >>>> >>>> PR target/60193 >>>> * config/i386/i386.c (ix86_expand_prologue): Use >>>> rax register as displacement for restoring %r10, %eax. >>>> >>>> Regression-tested for x86_64-unknown-linux-gnu, and >>>> x86_64-w64-mingw32, and i686-w64-mingw32. Ok for apply? >>> >>> No, you should check allocate to satisfy x86_64_immediate_operand and >>> put it into a temporary register if not. There is no need to always >>> force constant into a temporary. >> >> Well, in general I would agree to your statement. But in this case we >> have already the required value in rax-register loaded. So I don't >> see the advantage of using in case of <2^32 constant for those >> restore-operation. At least for code-size optimization it looks to me >> better and I am not aware that usage of register is here more >> expensive. I might be wrong about later. > > Ah, I was not aware of the fact that eax already holds the value. > However, there were some problems with the patch: eax RTX is > unnecessarily regenerated in the wrong mode, UNITS_PER_WORD should be > subtracted instead of added - you can use displacement+offset > addressing instead. > > Something like (untested) attached patch. > > Uros.
No, the patch I attached works fine. To substract here UNITS_PER_WORD is in fact a bug. As description see how we modify allocate on pushing. So for allocate of x * UNITS_PER_WORD with living rax, and r10, we will see following stack layout: [rax saved]: rsp = -1..-UNITS_PER_WORD1; [r10 saved]: rsp = -UNITS_PER_WORD-1..-2*UNITS_PER_WORD [reserved-stack]: rsp = -2*UNITS_PER_WORD-1.. -x*UNITS_PER_WORD So final rsp is -x * UNITS_PER_WORD and the value of allocate is (x - 2) * UNITS_PER_WORD. To restore r10, we can use [rsp+allocate] as (-2 * UNITS_PER_WORD) is its location. To restore rax we need to use [rsp+allocate+UNITS_PER_UNIT] as - UNITS_PER_WORD is its location. Regards. Kai
