Re: optimization/5969: When function is declared func(unsigned char v), v isn't truncated

[David Ashley <dash@xdr.com>]

The following reply was made to PR optimization/5969; it has been noted by GNATS.

From: David Ashley <dash@xdr.com>
To: dberlin@sources.redhat.com
Cc: gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org,
   nobody@gcc.gnu.org
Subject: Re: optimization/5969: When function is declared func(unsigned char v), v isn't truncated
Date: Sat, 16 Mar 2002 16:10:33 -0800

 >Synopsis: When function is declared func(unsigned char v), v isn't truncated
 >
 >Responsible-Changed-From-To: unassigned->dberlin
 >Responsible-Changed-By: dberlin
 >Responsible-Changed-When: Sat Mar 16 15:01:56 2002
 >Responsible-Changed-Why:
 >    Me
 >State-Changed-From-To: open->feedback
 >State-Changed-By: dberlin
 >State-Changed-When: Sat Mar 16 15:01:56 2002
 >State-Changed-Why:
 >    You have implicitly declared tst to take an int by using it before it's defined.
 >    Because it is inlined into main at -O2, and at that point it thinks it takes an int, it never performs the truncation.
 >    
 >    Any code after the tst function is defined to take an unsigned char will do the truncation.
 >    
 >    The problem is the code, not the compiler, AFAIK.
 >    The title of the bug report is misleading, you haven't declared func(unsigned char v), if you did, the problem would go away.
 >
 >http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5969
 
 I think compiled code should function exactly the same with or without -O2,
 but that's just my opinion. The problem here wasn't that the function was
 being called by 'c' code, it was being called by some ppc asm code. The
 first thing I did was turn on -Wall, then fixed all the warnings. But I didn't
 get any warnings about the ppc asm code calling the C function incorrectly,
 of course.
 
 How can the function be inlined into main even before the function is
 declared? And if it is being inlined once it is declared, that means a
 multi pass compiler or equivalent. So the compiler should know how to call
 the function by then.
 
 If your function is declared
 void func(unsigned char x)
 {
 	printf("sizeof(x)=%d\n",sizeof(x));
 	printf("x=%x\n",x);
 }
 
 You can call that from asm or from another code fragment with
 func(0x21);
 func(0x4321);
 and get different output. But sizeof prints out 1 for 1 byte. It seems to me
 inconsistent.
 
 As far as the title of the bug report being misleading, it's not like I'm
 an expert at reporting gcc bugs, there are basically no bugs :^). And it is
 difficult to explain within one line what is happening...
 
 Thanks---
 Dave
 dash@xdr.com