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* [gcc r12-2499] expmed: Fix store_integral_bit_field [PR101562]
@ 2021-07-23 17:56 Jakub Jelinek
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From: Jakub Jelinek @ 2021-07-23 17:56 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:8408d34570c9fe9f3d22a25a76df2a4c64f08477
commit r12-2499-g8408d34570c9fe9f3d22a25a76df2a4c64f08477
Author: Jakub Jelinek <jakub@redhat.com>
Date: Fri Jul 23 19:55:16 2021 +0200
expmed: Fix store_integral_bit_field [PR101562]
Our documentation says that paradoxical subregs shouldn't appear
in strict_low_part:
'(strict_low_part (subreg:M (reg:N R) 0))'
This expression code is used in only one context: as the
destination operand of a 'set' expression. In addition, the
operand of this expression must be a non-paradoxical 'subreg'
expression.
but on the testcase below that triggers UB at runtime
store_integral_bit_field emits exactly that.
The following patch fixes it by ensuring the requirement is satisfied.
2021-07-23 Jakub Jelinek <jakub@redhat.com>
PR rtl-optimization/101562
* expmed.c (store_integral_bit_field): Only use movstrict_optab
if the operand isn't paradoxical.
* gcc.c-torture/compile/pr101562.c: New test.
Diff:
---
gcc/expmed.c | 5 ++++-
gcc/testsuite/gcc.c-torture/compile/pr101562.c | 21 +++++++++++++++++++++
2 files changed, 25 insertions(+), 1 deletion(-)
diff --git a/gcc/expmed.c b/gcc/expmed.c
index 1fb63170be9..3143f38e057 100644
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -921,7 +921,10 @@ store_integral_bit_field (rtx op0, opt_scalar_int_mode op0_mode,
}
subreg_off = bitnum / BITS_PER_UNIT;
- if (validate_subreg (fieldmode, GET_MODE (arg0), arg0, subreg_off))
+ if (validate_subreg (fieldmode, GET_MODE (arg0), arg0, subreg_off)
+ /* STRICT_LOW_PART must have a non-paradoxical subreg as
+ operand. */
+ && !paradoxical_subreg_p (fieldmode, GET_MODE (arg0)))
{
arg0 = gen_rtx_SUBREG (fieldmode, arg0, subreg_off);
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr101562.c b/gcc/testsuite/gcc.c-torture/compile/pr101562.c
new file mode 100644
index 00000000000..ea4a5f7103a
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr101562.c
@@ -0,0 +1,21 @@
+/* PR rtl-optimization/101562 */
+
+struct S { char c; };
+void baz (struct S a, struct S b);
+
+void
+foo (void)
+{
+ struct S x[1];
+ *(short *)&x[0] = 256;
+ baz (x[0], x[1]);
+}
+
+void
+bar (void)
+{
+ struct S x[1];
+ x[0].c = 0;
+ x[1].c = 1;
+ baz (x[0], x[1]);
+}
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