New option?

[Sam Lauber]

I think an option -ftrapping-integer-math should be added 
to GCC that generates calls to the libgcc functions 
__XXXvdiX and ___XXXvsiX that call `abort()' for overflow 
instead of calls to the regular assembly instructions for 
that task. I.e. on x86, to add ebx + ebx into eax, instead 
of

  addl %ebx, %ebx
  movl %ebx, %eax

it would do

  pushl %ebx
  pushl %ebx
  call __addvsi2
  popl %eax

That would create runtime overhead for normal programs, and 
a *lot* of runtime overhead for alogrithms but it would 
prevent overflow from causing unpredictable results
(-finline-libgcc-functions anyone ;-).  But considering 
that most programs (and even most alogrithms) use a fair 
amount of constants, constant folding will reduce that 
overhead.  

Samuel Lauber
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