------- Comment #12 from developer at sandoe-acoustics dot co dot uk 2009-12-08 23:40 ------- (In reply to comment #11) > I think I understand why apple gcc42 does not show the problem: it does not > call ___divdc3: > > [macbook] f90/bug% diff -up pr42333_42.s pr42333_45.s > --- pr42333_42.s 2009-12-08 23:00:29.000000000 +0100 > +++ pr42333_45.s 2009-12-08 23:00:07.000000000 +0100 > ... > @@ -15,68 +15,61 @@ LCFI2: > movq %rax, -16(%rbp) > movabsq $9214364837600034815, %rax > movq %rax, -8(%rbp) > - movq -16(%rbp), %rax > - movq -8(%rbp), %rdx > - movq %rax, -24(%rbp) > - movsd -24(%rbp), %xmm1 > + movq -16(%rbp), %rdx > + movq -8(%rbp), %rax > movq %rdx, -24(%rbp) > movsd -24(%rbp), %xmm0 > - movapd %xmm0, %xmm2 > - addsd %xmm1, %xmm2 > - movapd %xmm0, %xmm3 > - subsd %xmm1, %xmm3 > - movsd LC1(%rip), %xmm0 > - movapd %xmm2, %xmm1 > - divsd %xmm0, %xmm1 > - movsd LC1(%rip), %xmm0 > - movapd %xmm3, %xmm2 > - divsd %xmm0, %xmm2 > - movapd %xmm2, %xmm0 > - movsd %xmm1, -24(%rbp) > - movq -24(%rbp), %rax > + movq %rax, -24(%rbp) > + movsd -24(%rbp), %xmm1 > + movsd LC2(%rip), %xmm3 > + movsd LC2(%rip), %xmm2 > + call ___divdc3 > movsd %xmm0, -24(%rbp) > movq -24(%rbp), %rdx > ... > > This also explain why the test compiled with -c and 4.5, but linked with 4.2 > fails. So my guess about the lazy complex division seems right in libm. Could > someone write a C code forcing the use of ___divdc3?
hmm.. indeed and, in fact, Apple's gcc-4.0 does not call ___divdc3 either (in fact, in a quick go at manipulation of options I couldn't find a case forcing either to call it). As far as generation of a test case is concerned - why not just use the asm generated by 4.5? I'll crank up a mini with D10 tomorrow (if possible).. if the asm gives a fault on D10 with 4.2 then that should be a file-able radar. .. seems likely that there are two things here: 1. we seem to be generating (probably) less efficient code than older versions of the compiler ... and 2. possibly the ___divdc3 in /usr/lib/libSystem is faulty? has anyone tried this on PPC? -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42333
