------- Comment #18 from zadeck at naturalbridge dot com 2007-10-06 13:07 ------- Subject: Re: [4.3 regression]: wrong code with -fforce-addr
ubizjak at gmail dot com wrote: > ------- Comment #16 from ubizjak at gmail dot com 2007-10-06 06:49 ------- > (In reply to comment #14) > >> The testcase works for me, that is, it produces the expected output good.out. >> > > Uh, you have to un-comment the line 315 of the comunpack.f test. The testcase, > as attached, produces good code. Un-commenting line 315, you will get: > > .L80: > movl $0x40000000, (%esp) > call powf > fstps -152(%ebp) > negl -136(%ebp) > fildl -136(%ebp) > fstps 4(%esp) > movl $0x41200000, (%esp) > call powf > > Note that only one argument is loaded to the stack before first powf. > > Without -fforce-address on un-commented testcase, we got: > > .L80: > fildl -132(%ebp) > fstps 4(%esp) > movl $0x40000000, (%esp) > call powf > fstps -140(%ebp) > negl -128(%ebp) > fildl -128(%ebp) > fstps 4(%esp) > movl $0x41200000, (%esp) > call powf > > > ian, As you may remember, the dse code assumes that it can "see" all of the stores that are frame_related. It appears that with the -fforce-addr option this is not true. in this particular example, a frame related pointer gets loaded into register 755 very early on (in a different block) and since const calls only disqualify frame-related stores, (since they may push params onto the stack), the parameter push is considered dead. My question to you, is the proper fix to check flag_force-addr and if it is set just assume that every store may be frame related or is there some sort of tea leaf that i might have access to know that reg 755 is used in this way? (note that you have to jump thru a few hoops to recreate this, since comunpack.f is in a separate attachment from the rest of the code and you have to uncomment line 315 to recreate the bug.) Kenny -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33638
