Hi Roger,
The patch looks sane. Have you run dejagnu test suite?
Thanks,
Claudiu
-----Original Message-----
From: Roger Sayle <ro...@nextmovesoftware.com>
Sent: Friday, September 29, 2023 6:54 PM
To: gcc-patches@gcc.gnu.org
Cc: Claudiu Zissulescu <claz...@synopsys.com>
Subject: [ARC PATCH] Use rlc r0,0 to implement scc_ltu (i.e. carry_flag ? 1 : 0)
This patch teaches the ARC backend that the contents of the carry flag can be
placed in an integer register conveniently using the "rlc rX,0"
instruction, which is a rotate-left-through-carry using zero as a source.
This is a convenient special case for the LTU form of the scc pattern.
unsigned int foo(unsigned int x, unsigned int y) {
return (x+y) < x;
}
With -O2 -mcpu=em this is currently compiled to:
foo: add.f 0,r0,r1
mov_s r0,1 ;3
j_s.d [blink]
mov.hs r0,0
[which after an addition to set the carry flag, sets r0 to 1, followed by a
conditional assignment of r0 to zero if the carry flag is clear]. With the new
define_insn/optimization in this patch, this becomes:
foo: add.f 0,r0,r1
j_s.d [blink]
rlc r0,0
This define_insn is also a useful building block for implementing shifts and
rotates.
Tested on a cross-compiler to arc-linux (hosted on x86_64-pc-linux-gnu), and a
partial tool chain, where the new case passes and there are no new regressions.
Ok for mainline?
2023-09-29 Roger Sayle <ro...@nextmovesoftware.com>
gcc/ChangeLog
* config/arc/arc.md (CC_ltu): New mode iterator for CC and CC_C.
(scc_ltu_<mode>): New define_insn to handle LTU form of scc_insn.
(*scc_insn): Don't split to a conditional move sequence for LTU.
gcc/testsuite/ChangeLog
* gcc.target/arc/scc-ltu.c: New test case.
Thanks in advance,
Roger
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