Null pointer check elimination

[Jeff Law]

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On 03/08/11 22:23, richardcavell@mail.com wrote:
> 
> foo (char *x)
> {
>  char ret = *x;
> 
>  if (x)
>    com();
>  else
>    bar();
>  return ret;
> }
> 
>> It is expected that the compiler will eliminate the pointer check with 
> the option '-fdelete-null-pointer-checks' or with >the option -O2, -O3,
> or -Os.
> 
> Hang on, why would it eliminate the null pointer check, if the null
> pointer check is in the source code?  Are you assuming that the compiler
> knows for certain that x is non zero when it compiles the function?
X was dereferenced in the initialization of ret.  Dereferencing NULL is
not a ANSI/ISO confirming program and the compiler is free to optimize
away any checks of X against NULL that are dominated by the dereference
of X.

jeff
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