Could you file a bugzilla for that? https://gcc.gnu.org/bugzilla/enter_bug.cgi?product=gcc
On Thu, Aug 5, 2021 at 3:34 PM Stefan Kanthak <stefan.kant...@nexgo.de> wrote: > > Hi, > > targeting AMD64 alias x86_64 with -O3, GCC 10.2.0 generates the > following code (17 instructions using 78 bytes, plus 6 quadwords > using 48 bytes) for __builtin_ceil() when -msse4.1 is NOT given: > > .text > 0: f2 0f 10 15 10 00 00 00 movsd .LC1(%rip), %xmm2 > 4: R_X86_64_PC32 .rdata > 8: f2 0f 10 25 00 00 00 00 movsd .LC0(%rip), %xmm4 > c: R_X86_64_PC32 .rdata > 10: 66 0f 28 d8 movapd %xmm0, %xmm3 > 14: 66 0f 28 c8 movapd %xmm0, %xmm1 > 18: 66 0f 54 da andpd %xmm2, %xmm3 > 1c: 66 0f 2e e3 ucomisd %xmm3, %xmm4 > 20: 76 2b jbe 4d <_ceil+0x4d> > 22: f2 48 0f 2c c0 cvttsd2si %xmm0, %rax > 27: 66 0f ef db pxor %xmm3, %xmm3 > 2b: f2 0f 10 25 20 00 00 00 movsd 0x20(%rip), %xmm4 > 2f: R_X86_64_PC32 .rdata > 33: 66 0f 55 d1 andnpd %xmm1, %xmm2 > 37: f2 48 0f 2a d8 cvtsi2sd %rax, %xmm3 > 3c: f2 0f c2 c3 06 cmpnlesd %xmm3, %xmm0 > 41: 66 0f 54 c4 andpd %xmm4, %xmm0 > 45: f2 0f 58 c3 addsd %xmm3, %xmm0 > 49: 66 0f 56 c2 orpd %xmm2, %xmm0 > 4d: c3 retq > > .rdata > .align 8 > 0: 00 00 00 00 .LC0: .quad 0x1.0p52 > 00 00 30 43 > 00 00 00 00 > 00 00 00 00 > .align 16 > 10: ff ff ff ff .LC1: .quad ~(-0.0) > ff ff ff 7f > 18: 00 00 00 00 .quad 0.0 > 00 00 00 00 > .align 8 > 20: 00 00 00 00 .LC2: .quad 0x1.0p0 > 00 00 f0 3f > 00 00 00 00 > 00 00 00 00 > .end > > JFTR: in the best case, the memory accesses cost several cycles, > while in the worst case they yield a page fault! > > > Properly optimized, faster and shorter code, using just 15 instructions > in 65 bytes, WITHOUT superfluous constants, thus avoiding costly memory > accesses and saving at least 32 bytes, follows: > > .intel_syntax > .equ BIAS, 1023 > .text > 0: f2 48 0f 2c c0 cvttsd2si rax, xmm0 # rax = trunc(argument) > 5: 48 f7 d8 neg rax > # jz .L0 # argument zero? > 8: 70 36 jo .L0 # argument indefinite? > # argument overflows > 64-bit integer? > a: 48 f7 d8 neg rax > d: f2 48 0f 2a c8 cvtsi2sd xmm1, rax # xmm1 = trunc(argument) > 12: 48 a1 00 00 00 mov rax, BIAS << 52 > 19: 00 00 00 f0 3f > 1c: 66 48 0f 6e d0 movq xmm2, rax # xmm2 = 0x1.0p0 > 21: f2 0f 10 d8 movsd xmm3, xmm0 # xmm3 = argument > 25: f2 0f c2 d9 02 cmplesd xmm3, xmm1 # xmm3 = (argument <= > trunc(argument)) ? ~0L : 0L > 2a: 66 0f 55 da andnpd xmm3, xmm2 # xmm3 = (argument <= > trunc(argument)) ? 0.0 : 1.0 > 2e: f2 0f 58 d9 addsd xmm3, xmm1 # xmm3 = (argument > > trunc(argument)) ? 1.0 : 0.0 > # + trunc(argument) > # = ceil(argument) > 32: 66 0f 73 d0 3f psrlq xmm0, 63 > 37: 66 0f 73 f0 3f psllq xmm0, 63 # xmm0 = (argument & -0.0) > ? -0.0 : 0.0 > 3c: 66 0f 56 c3 orpd xmm0, xmm3 # xmm0 = ceil(argument) > 40: c3 .L0: ret > .end > > regards > Stefan -- BR, Hongtao
