From: "Roger Sayle" <roger@nextmovesoftware.com>
To: <gcc-patches@gcc.gnu.org>
Subject: [x86 PATCH] PR target/106577: force_reg may clobber operands during split.
Date: Fri, 12 Aug 2022 21:40:52 +0100 [thread overview]
Message-ID: <002201d8ae8b$d11fa9b0$735efd10$@nextmovesoftware.com> (raw)
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This patch fixes PR target/106577 which is a recent ICE on valid regression
caused by my introduction of a *testti_doubleword pre-reload splitter in
i386.md. During the split pass before reload, this converts the virtual
*testti_doubleword into an *andti3_doubleword and *cmpti_doubleword,
checking that any immediate operand is a valid "x86_64_hilo_general_operand"
and placing it into a TImode register using force_reg if it isn't.
The unexpected behaviour (that caught me out) is that calling force_reg
may occasionally clobber the contents of the global operands array, or
more accurately recog_data.operand[0], which means that by the time
split_XXX calls gen_split_YYY the replacement insn's operands have been
corrupted.
It's difficult to tell who (if anyone is at fault). The re-entrant
stack trace (for the attached PR) looks like:
gen_split_203 (*testti_doubleword) calls
force_reg calls
emit_move_insn calls
emit_move_insn_1 calls
gen_movti calls
ix86_expand_move calls
ix86_convert_const_wide_int_to_broadcast calls
ix86_vector_duplicate_value calls
recog_memoized calls
recog.
By far the simplest and possibly correct fix is rather than attempt
to push and pop recog_data, to simply (in pre-reload splits) save a
copy of any operands that will be needed after force_reg, and use
these copies afterwards. Many pre-reload splitters avoid this issue
using "[(clobber (const_int 0))]" and so avoid gen_split_YYY functions,
but in our case we still need to save a copy of operands[0] (even if we
call emit_insn or expand_* ourselves), so we might as well continue to
use the conveniently generated gen_split.
This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32},
with no new failures. Ok for mainline?
2022-08-12 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
PR target/106577
* config/i386/i386.md (*testti_doubleword): Preserve a copy of
operands[0], and move initialization of operands[2] later, as the
call to force_reg may clobber the contents of the operands array.
gcc/testsuite/ChangeLog
PR target/106577
* gcc.target/i386/pr106577.c: New test case.
Thanks,
Roger
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diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 2fde8cd..e9232cd 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -9772,9 +9772,12 @@
(clobber (reg:CC FLAGS_REG))])
(set (reg:CCZ FLAGS_REG) (compare:CCZ (match_dup 2) (const_int 0)))]
{
- operands[2] = gen_reg_rtx (TImode);
+ /* Calling force_reg may clobber operands[0]. */
+ rtx save_op0 = operands[0];
if (!x86_64_hilo_general_operand (operands[1], TImode))
operands[1] = force_reg (TImode, operands[1]);
+ operands[2] = gen_reg_rtx (TImode);
+ operands[0] = save_op0;
})
;; Combine likes to form bit extractions for some tests. Humor it.
diff --git a/gcc/testsuite/gcc.target/i386/pr106577.c b/gcc/testsuite/gcc.target/i386/pr106577.c
new file mode 100644
index 0000000..4e35031
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr106577.c
@@ -0,0 +1,7 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2 -mavx" } */
+
+int i;
+void foo(void) {
+ i ^= !(((unsigned __int128)0xf0f0f0f0f0f0f0f0 << 64 | 0xf0f0f0f0f0f0f0f0) & i);
+}
next reply other threads:[~2022-08-12 20:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-12 20:40 Roger Sayle [this message]
2022-08-15 7:45 ` Richard Biener
2022-08-16 8:14 ` Richard Sandiford
2022-08-16 8:26 ` Richard Biener
2022-08-16 9:02 ` Richard Sandiford
2022-12-02 9:39 ` [PATCH] i386: Save/restore recog_data in ix86_vector_duplicate_value [PR106577] Jakub Jelinek
2022-12-02 9:51 ` Uros Bizjak
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