Re: RFC: remove find_replacement. (pr24912 / pr25335)

[Bernd Schmidt <bernds_cb1 at t-online dot de>]

Bernd Schmidt wrote:
> I've tested the patch below against an i686-linux, an 
> arm-elf, a bfin-elf, and an sh-elf compiler, and did not once manage to 
> produce different output before and after the patch.  I assume my theory 
> is correct that whatever this code does is also done by reload_cse. 
> Unless someone finds a testcase that has a regression or has another 
> valid reason for an objection, I'll install this in a day or two.

The tests I mentioned above involved compiling every file in gcc from .i 
to .s.  Joern suggested I also try Toshi's stress test suite; I had an 
older version of it lying around and used this as well as all files from 
Crafty and my own UAE against an sh-elf and an s390-linux compiler.  I 
managed to produce only two differences in output; in one file a store 
instruction moved by a couple of instructions, in another file (Crafty's 
book.i) there was one genuine case of a missed CSE opportunity.  We have

r1 = 99;
[stuff, involving a use of r1]
r0 = 99;
fpul = r0;

which I'm certain could be fixed by making reload_cse a bit more clever.

But I don't think one instance of a minor lost optimization across a 
test of several platforms is enough to defend keeping this code in, 
especially since it's making further simplification more difficult than 
necessary.

> 	* reload1.c (emit_input_reload_insns): Delete code that tries to
> 	inherit using find_equiv_reg.

Hence, I bootstrapped and regression tested this on i686-linux, and 
committed it.

Ulrich, can you retry Joern's original patch on your machine?


Bernd