gcc 2.2.2: "unsigned preserving" rule of "-traditional" causes problem

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1 total messages Started by Peter Magnusson Wed, 29 Jul 1992 23:10

#328

Author: Peter Magnusson
Date: Wed, 29 Jul 1992 23:10

85 lines
2155 bytes

Comparing an "int" with a 32-bit constant generates strange code when the
"traditional" flag is selected.

Gcc version 2.2.2 (running on SPARCstation ELC 4/25 SunOS 4.1.2).

The following bit of code:

   int
     main()
   {
     int a,b;
     b = 0x80000000;
     if (b >= 0x80000000)
       a = 0;
     else
       a = 1;
   }

Generates the following code with "gcc -S":

.text
        .align 4
        .global _main
        .proc   04
_main:
        !#PROLOGUE# 0
        save %sp,-144,%sp
        !#PROLOGUE# 1
        call ___main,0
        nop
        sethi %hi(-2147483648),%o0
        st %o0,[%fp-24]
        ld [%fp-24],%o0
        sethi %hi(2147483647),%o2
        or %o2,%lo(2147483647),%o1
        cmp %o0,%o1
        bleu L2                      <========
        nop
        st %g0,[%fp-20]
        b,a L3
L2:
        mov 1,%o0
        st %o0,[%fp-20]
L3:
L1:
        ret
        restore

When compiled with "gcc -S -traditional", the code is:

.text
        .align 4
        .global _main
        .proc   04
_main:
        !#PROLOGUE# 0
        save %sp,-144,%sp
        !#PROLOGUE# 1
        call ___main,0
        nop
        sethi %hi(-2147483648),%o0
        st %o0,[%fp-24]
        ld [%fp-24],%o0
        sethi %hi(2147483647),%o2
        or %o2,%lo(2147483647),%o1
        cmp %o0,%o1
        ble L2                         <======= !!!!
        nop
        st %g0,[%fp-20]
        b,a L3
L2:
        mov 1,%o0
        st %o0,[%fp-20]
L3:
L1:
        ret
   

Notice the change. The constant is decremented but the comparison is such that
the expression evaluates to false!


Peter Magnusson
Swedish Institute of Computer Science
psm@sics.se

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