[Bug c/11399] gcc 3.3.1 miscompiles an if - else if - else statement with O1 on ia64

["wilson at tuliptree dot org" <gcc-bugzilla at gcc dot gnu dot org>]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11399



------- Additional Comments From wilson at tuliptree dot org  2003-07-04 05:07 -------
Subject: Re:  New: gcc 3.3.1 miscompiles an if - else if - else
 statement with O1 on ia64

ianw at gelato dot unsw dot edu dot au wrote:
>         cmp4.ne p6, p7 = 0, r8
>         addl r14 = @ltoffx("a string"), r1
>         ;;
>         (p7) addl r14 = 1, r0               <---- set r14 to 1
>         ;;
>         .mmb
>         (p6) ld8.mov r8 = [r14], "a string" <---- segfault

You are misreading the code.  IPF has predicated execution.  An 
instruction executes only if the qualifying predicate is true.  In this 
case, the two instructions use different predicate registers p6/p7, and 
because this is a predicate register pair we are guaranteed that at most 
one is true, i.e. they are mutex in IPF terminology.

The 3.3 and 3.4 .s files you put in the bug report don't match your 
annotated assembly sample.  The annotated code has p6/p7 predicate 
register usage.  The 3.3/3.4 .s output have only p7 predicate register 
usage.

I am unable to reproduce your assembly output using a x86-x-ia64 cross 
compiler using 3.3 branch last updated a few days ago.

I don't have access to IPF hardware, so I am unfortunately not able to 
run the example.

Jim