mirror of
https://github.com/gcc-mirror/gcc.git
synced 2026-05-06 14:59:39 +02:00
022afdcb9b
So this is a trivial little bug we found doing some comparisons against LLVM.
For the function sub2 in load-immediate.c we get this code:
li a5,-32768
sh a5,0(a0)
xori a5,a5,-1
sh a5,0(a1)
Note carefully that li+xori. There's a slightly better sequence here from an
encoding standpoint. Instead of using xori we can adjust the synthesis
sequence to target an "addi" for that statement and in doing so we can save two
code bytes of space.
The xori sequence was used because we can't do this in gcc:
(set (dest:HI) (const_int 0x8000))
We're in HI mode so the constant must be sign extended from bit 15 to a
HOST_WIDE_INT.
Fixing this isn't hard. The key is realizing the vast majority of the time we
really don't want/need to load in HImode and in fact we're typically going to
be generating objects in word_mode. So instead of passing in the pre-promoted
mode, pass in the post-promoted mode.
That's fine and good with one caveat. CSE fails to use NEG/NOT to derive a
new constant from an older constant, even if the cost is smaller, which caused
a code quality regression elsewhere on the RISC-V port. So this patch adjusts
CSE ever-so-slightly to allow it to derive constants from a previous constant
using NOT/NEG in a fairly obvious way.
This has been in my tester for a while, so it's been through the usual
bootstrap & regression test on the Pioneer, BPI, x86 and aarch64 and others as
well as testing across the various embedded targets.
Waiting on pre-commit testing to do its thing.
PR target/124559
gcc/
* config/riscv/riscv-protos.h (riscv_move_integer): Drop mode argument.
* config/riscv/riscv.cc (riscv_move_integer): Pass mode after promotions
to riscv_build_integer. All callers changed.
* config/riscv/riscv.md: Corresponding changes.
* cse.cc (cse_insn): Try to derive one constant from another using NOT/NEG.
This directory contains the GNU Compiler Collection (GCC). The GNU Compiler Collection is free software. See the files whose names start with COPYING for copying permission. The manuals, and some of the runtime libraries, are under different terms; see the individual source files for details. The directory INSTALL contains copies of the installation information as HTML and plain text. The source of this information is gcc/doc/install.texi. The installation information includes details of what is included in the GCC sources and what files GCC installs. See the file gcc/doc/gcc.texi (together with other files that it includes) for usage and porting information. An online readable version of the manual is in the files gcc/doc/gcc.info*. See http://gcc.gnu.org/bugs/ for how to report bugs usefully. Copyright years on GCC source files may be listed using range notation, e.g., 1987-2012, indicating that every year in the range, inclusive, is a copyrightable year that could otherwise be listed individually.