mirror of
git://gcc.gnu.org/git/gcc.git
synced 2025-03-30 13:21:20 +08:00
7de23b8c53
This change fixes a bug in the AArch64 backend. Currently, we accept an
odd sign_extract representation of addresses, but don't accept that same
odd form of address as an LEA.
This is the cause of PR96998. In the testcase given in the PR, combine
produces:
(insn 9 8 10 3 (set (mem:SI (plus:DI (sign_extract:DI (mult:DI (subreg:DI (reg/v:SI 92 [ g ]) 0)
(const_int 4 [0x4]))
(const_int 34 [0x22])
(const_int 0 [0]))
(reg/f:DI 96)) [3 *i_5+0 S4 A32])
(asm_operands:SI ("") ("=Q") 0 []
[]
[] test.c:11)) "test.c":11:5 -1
(expr_list:REG_DEAD (reg/v:SI 92 [ g ])
(nil)))
Then LRA reloads the address and we ICE because we fail to recognize the
sign_extract outside the mem:
(insn 33 8 34 3 (set (reg:DI 100)
(sign_extract:DI (ashift:DI (subreg:DI (reg/v:SI 92 [ g ]) 0)
(const_int 2 [0x2]))
(const_int 34 [0x22])
(const_int 0 [0]))) "test.c":11:5 -1
(nil))
The aarch64 changes here remove the support for this sign_extract
representation of addresses, fixing PR96998. Now this by itself would
regress code quality, so this change is paired with an improvement to
combine which prevents an extract rtx from being emitted in this case:
we now write the rtx above as a shift of an extend, which allows the
combination to go ahead.
Prior to this, combine.c:make_extraction() identified where we can emit
an ashift of an extend in place of an extraction, but failed to make the
corresponding canonicalization/simplification when presented with a mult
by a power of two. Such a representation is canonical when representing
a left-shifted address inside a mem.
This change remedies this situation. For rtxes such as:
(mult:DI (subreg:DI (reg:SI r) 0) (const_int 2^n))
where the bottom 32 + n bits are valid (the higher-order bits are
undefined) and make_extraction() is being asked to sign_extract the
lower (valid) bits, after the patch, we rewrite this as:
(mult:DI (sign_extend:DI (reg:SI r)) (const_int 2^n))
instead of using a sign_extract.
gcc/ChangeLog:
PR target/96998
* combine.c (make_extraction): Also handle shifts written as
(mult x 2^n), avoid creating an extract rtx for these.
* config/aarch64/aarch64.c (aarch64_is_extend_from_extract): Delete.
(aarch64_classify_index): Remove extract-based address handling.
(aarch64_strip_extend): Likewise.
(aarch64_rtx_arith_op_extract_p): Likewise, remove now-unused parameter.
Update callers...
(aarch64_rtx_costs): ... here.
gcc/testsuite/ChangeLog:
PR target/96998
* gcc.c-torture/compile/pr96998.c: New test.
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.