[Bug rtl-optimization/6585] Redundant store/load instruction pairs on ix86

[steven at gcc dot gnu dot org]

------- Additional Comments From steven at gcc dot gnu dot org  2005-06-26 13:35 -------
Today's results ("-O2 -m32 -march=i686 -mtune=i686 -fomit-frame-pointer"): 
 
        .file   "t.c" 
        .text 
        .p2align 4,,15 
.globl mul 
        .type   mul, @function 
mul: 
        subl    $12, %esp               # get space to save three registers 
        movl    %ebx, (%esp)            # save %ebx 
        movl    20(%esp), %edx          # %edx <- a1  COULD GO INTO %esi 
        movl    28(%esp), %ebx          # %ebx <- b1  COULD GO INTO %edi 
        movl    16(%esp), %eax          # %eax <- a0 
        movl    24(%esp), %ecx          # %ecx <- b0 
        movl    %esi, 4(%esp)           # save %esi 
        movl    %edx, %esi              # %esi <- a1 
        movl    %edi, 8(%esp)           # save %edi 
        movl    %ebx, %edi              # %edi <- b1 
        movl    (%esp), %ebx            # restore %ebx 
        imull   %eax, %edi              # %edi <- a0*b1 
        imull   %ecx, %esi              # %esi <- b0*a1 
        mull    %ecx                    # %edx:%eax := a0*b0 
        addl    %edi, %esi              # %esi <- a0*b1 + b0*a1 
        movl    8(%esp), %edi           # restore %edi 
        leal    (%esi,%edx), %edx       # %edx <- a0*b1 + b0*a1 + hi(a0*b0) 
        movl    4(%esp), %esi           # %restore %esi 
        addl    $12, %esp               # free stack space 
        ret                             # return result in %edx:%eax 
        .size   mul, .-mul 
        .ident  "GCC: (GNU) 4.1.0 20050626 (experimental)" 
        .section        .note.GNU-stack,"",@progbits 
 
There are still the questionable moves through %ebx and %edx, but it is 
still better than before. 
 

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=6585