Bug#894840: clang: baseline cpu violation on i386

[Andreas Beckmann]

Package: clang
Version: baseline cpu violation on i386
Severity: serious

Hi,

all clang versions (at least since wheezy) by default generate code for
a cpu that is newer than the baseline cpu on i386. On clang-6.0 the
default is apparently pentium4 which has sse2 (among other features),
but that is not available on the baseline cpu, which is currently i686.

>From clang on wheezy/i386 (but the result is equivalent on newer releases
and also on amd64 with -m32) - clang generates sse code for some floating
point arithmetic, while gcc generates x87 code:

$ echo 'double fma(double a, double b, double c) { return a * b + c; }' | clang -O2 -S -xc - -o-
        .file   "-"
        .text
        .globl  fma
        .align  16, 0x90
        .type   fma, at function
fma:                                    # @fma
# BB#0: 
        subl    $12, %esp
        movsd   16(%esp), %xmm0
        mulsd   24(%esp), %xmm0
        addsd   32(%esp), %xmm0
        movsd   %xmm0, (%esp)
        fldl    (%esp)
        addl    $12, %esp
        ret
.Ltmp0: 
        .size   fma, .Ltmp0-fma


        .section        ".note.GNU-stack","", at progbits

$ echo 'double fma(double a, double b, double c) { return a * b + c; }' | gcc -O2 -S -xc - -o-
        .file   ""
        .text
        .p2align 4,,15
        .globl  fma
        .type   fma, @function
fma:
.LFB0:  
        .cfi_startproc
        fldl    12(%esp)
        fmull   4(%esp)
        faddl   20(%esp)
        ret
        .cfi_endproc
.LFE0:  
        .size   fma, .-fma
        .ident  "GCC: (Debian 4.7.2-5) 4.7.2"
        .section        .note.GNU-stack,"", at progbits


Andreas