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Re: [PATCH,sim/sh] lvalue casts
- From: Daniel Jacobowitz <drow at false dot org>
- To: Ralf Corsepius <ralf dot corsepius at rtems dot org>
- Cc: GDB Patches <gdb-patches at sources dot redhat dot com>
- Date: Thu, 16 Jun 2005 23:12:55 -0400
- Subject: Re: [PATCH,sim/sh] lvalue casts
- References: <1115047102.24385.376.camel@mccallum.corsepiu.local>
On Mon, May 02, 2005 at 05:18:22PM +0200, Ralf Corsepius wrote:
> Hi,
>
> gcc-4.0.0 chokes on with an "invalid lvalue" error on the code generated
> by sh/gencode.c (gdb-CVS mainline).
>
> The patch below seems to fix this issue for me.
>
> AFAIS, the "(unsigned int) R[]" cast are just superfluous.
Sorry about the delay.
> 2005-05-02 Ralf Corsepius <ralf.corsepius@rtems.org>
>
> * gencode.c (divu R0,<REG_N>): Remove lvalue casts to please gcc4.
>
>
> Index: gencode.c
> ===================================================================
> RCS file: /cvs/src/src/sim/sh/gencode.c,v
> retrieving revision 1.31
> diff -u -r1.31 gencode.c
> --- gencode.c 14 Apr 2005 20:16:06 -0000 1.31
> +++ gencode.c 2 May 2005 15:10:03 -0000
> @@ -215,7 +215,7 @@
> "RAISE_EXCEPTION_IF_IN_DELAY_SLOT ();",
> "if (R0 == 0)",
> " R[n] = 0xffffffff;",
> - "else (unsigned int) R[n] = (unsigned int) R[n] / (unsigned int) R0;",
> + "else R[n] = R[n] / (unsigned int) R0;",
> "L (n);",
> },
The second cast definitely can go; int will be promoted to unsigned int
automatically, and that's a well defined conversion. However, the
other half is dodgier:
[#3] Otherwise, the new type is signed and the value cannot
be represented in it; either the result is implementation-
defined or an implementation-defined signal is raised.
So for 0xffffffff / 1u, the result is implementation-defined.
Unfortunate. We'll just have to propogate the assumption that
the implementation uses the sensible definition... I've committed the
below. Now I can build GDB for sh-elf using gcc 4.0, though not with
-Werror yet.
--
Daniel Jacobowitz
CodeSourcery, LLC
2005-06-16 Daniel Jacobowitz <dan@codesourcery.com>
* gencode.c (tab): Avoid lvalue casts. Suggested by
Ralf Corsepius <ralf.corsepius@rtems.org>.
Index: gencode.c
===================================================================
RCS file: /cvs/src/src/sim/sh/gencode.c,v
retrieving revision 1.31
diff -u -p -r1.31 gencode.c
--- gencode.c 14 Apr 2005 20:16:06 -0000 1.31
+++ gencode.c 17 Jun 2005 03:06:38 -0000
@@ -215,7 +215,9 @@ op tab[] =
"RAISE_EXCEPTION_IF_IN_DELAY_SLOT ();",
"if (R0 == 0)",
" R[n] = 0xffffffff;",
- "else (unsigned int) R[n] = (unsigned int) R[n] / (unsigned int) R0;",
+ "/* FIXME: The result may be implementation-defined if it is outside */",
+ "/* the range of signed int (i.e. if R[n] was negative and R0 == 1). */",
+ "else R[n] = R[n] / (unsigned int) R0;",
"L (n);",
},
{ "n", "0n", "mulr R0,<REG_N>", "0100nnnn10000000",