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From: Jakub Jelinek <jakub@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-2499] expmed: Fix store_integral_bit_field [PR101562] Date: Fri, 23 Jul 2021 17:56:16 +0000 (GMT) [thread overview] Message-ID: <20210723175616.7266D385C41C@sourceware.org> (raw) 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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