Re: mipsisa32-unknown-elf-as: Error: too large constant specified

[Ian Lance Taylor <ian at wasabisystems dot com>]

fnf@intrinsity.com (Fred Fish) writes:

> Before I report this as a bug, does anyone know if this is a
> deliberate change in behavior or a bug.  Given the assembly input:
> 
> 	$ cat a.s
> 	        and $26, $26, ~(0xE0000000)
> 
> an older assembler handles this just fine by using the $at register:
> 
> 	$ /usr/local/sourceware/bin/mipsisa32-unknown-elf-as -v a.s
> 	GNU assembler version 2.14.90 (mipsisa32-unknown-elf) using BFD version 2.14.90 20030830
> 	$ /usr/local/sourceware/bin/mipsisa32-unknown-elf-objdump --disassemble a.o
> 
> 	a.o:     file format elf32-bigmips
> 
> 	Disassembly of section .text:
> 
> 	00000000 <.text>:
> 	   0:   3c011fff        lui     at,0x1fff
> 	   4:   3421ffff        ori     at,at,0xffff
> 	   8:   0341d024        and     k0,k0,at
> 
> however a current build, using current CVS sources, treats it as an error:
> 
> 	$ /build/sourceware/binutils/T-mipsisa32-unknown-elf/gas/as-new -v a.s
> 	GNU assembler version 2.14.90 (mipsisa32-unknown-elf) using BFD version 2.14.90 20031014
> 	a.s: Assembler messages:
> 	a.s:1: Error: too large constant specified

Well, this example works fine:
	and $26, $26, (~(0xE0000000) & 0xffffffff)

Whether this is a bug or not is difficult to say.  What is the
precision of the ~ operator?  What's happening is that ~0xe0000000 is
being turned into 0xffffffff1fffffff.  That constant is indeed too
large.  Naturally you want ~0xe0000000 to be 0x1fffffff.  But,
currently, for any MIPS target, the assembler will do 64-bit
arithmetic.  Maybe for a 32 bit MIPS target the assembler should know
to use 32-bit arithmetic.  Unfortunately that would not be a trivial
change.

Ian