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From: Jakub Jelinek <jakub@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r10-10622] stor-layout: Create DECL_BIT_FIELD_REPRESENTATIVE even for bitfields in unions [PR101062] Date: Tue, 10 May 2022 08:18:54 +0000 (GMT) [thread overview] Message-ID: <20220510081854.4BCC338346A8@sourceware.org> (raw) https://gcc.gnu.org/g:0a278a8e2a95abe2bdad50ffd820b31363758a78 commit r10-10622-g0a278a8e2a95abe2bdad50ffd820b31363758a78 Author: Jakub Jelinek <jakub@redhat.com> Date: Wed Jun 16 12:17:55 2021 +0200 stor-layout: Create DECL_BIT_FIELD_REPRESENTATIVE even for bitfields in unions [PR101062] The following testcase is miscompiled on x86_64-linux, the bitfield store is implemented as a RMW 64-bit operation at d+24 when the d variable has size of only 28 bytes and scheduling moves in between the R and W part a store to a different variable that happens to be right after the d variable. The reason for this is that we weren't creating DECL_BIT_FIELD_REPRESENTATIVEs for bitfields in unions. The following patch does create them, but treats all such bitfields as if they were in a structure where the particular bitfield is the only field. 2021-06-16 Jakub Jelinek <jakub@redhat.com> PR middle-end/101062 * stor-layout.c (finish_bitfield_representative): For fields in unions assume nextf is always NULL. (finish_bitfield_layout): Compute bit field representatives also in unions, but handle it as if each bitfield was the only field in the aggregate. * gcc.dg/pr101062.c: New test. (cherry picked from commit b4b50bf2864e09f028a39a3f460222632c4d7348) Diff: --- gcc/stor-layout.c | 26 +++++++++++++++----------- gcc/testsuite/gcc.dg/pr101062.c | 29 +++++++++++++++++++++++++++++ 2 files changed, 44 insertions(+), 11 deletions(-) diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c index 57c8a2516d9..e805e6912a7 100644 --- a/gcc/stor-layout.c +++ b/gcc/stor-layout.c @@ -2059,9 +2059,14 @@ finish_bitfield_representative (tree repr, tree field) bitsize = (bitsize + BITS_PER_UNIT - 1) & ~(BITS_PER_UNIT - 1); /* Now nothing tells us how to pad out bitsize ... */ - nextf = DECL_CHAIN (field); - while (nextf && TREE_CODE (nextf) != FIELD_DECL) - nextf = DECL_CHAIN (nextf); + if (TREE_CODE (DECL_CONTEXT (field)) == RECORD_TYPE) + { + nextf = DECL_CHAIN (field); + while (nextf && TREE_CODE (nextf) != FIELD_DECL) + nextf = DECL_CHAIN (nextf); + } + else + nextf = NULL_TREE; if (nextf) { tree maxsize; @@ -2154,13 +2159,6 @@ finish_bitfield_layout (tree t) tree field, prev; tree repr = NULL_TREE; - /* Unions would be special, for the ease of type-punning optimizations - we could use the underlying type as hint for the representative - if the bitfield would fit and the representative would not exceed - the union in size. */ - if (TREE_CODE (t) != RECORD_TYPE) - return; - for (prev = NULL_TREE, field = TYPE_FIELDS (t); field; field = DECL_CHAIN (field)) { @@ -2220,7 +2218,13 @@ finish_bitfield_layout (tree t) if (repr) DECL_BIT_FIELD_REPRESENTATIVE (field) = repr; - prev = field; + if (TREE_CODE (t) == RECORD_TYPE) + prev = field; + else if (repr) + { + finish_bitfield_representative (repr, field); + repr = NULL_TREE; + } } if (repr) diff --git a/gcc/testsuite/gcc.dg/pr101062.c b/gcc/testsuite/gcc.dg/pr101062.c new file mode 100644 index 00000000000..6c37ed88885 --- /dev/null +++ b/gcc/testsuite/gcc.dg/pr101062.c @@ -0,0 +1,29 @@ +/* PR middle-end/101062 */ +/* { dg-do run } */ +/* { dg-options "-O2 -fno-toplevel-reorder -frename-registers" } */ + +union U { signed b : 5; }; +int c; +volatile union U d[7] = { { 8 } }; +short e = 1; + +__attribute__((noipa)) void +foo () +{ + d[6].b = 0; + d[6].b = 0; + d[6].b = 0; + d[6].b = 0; + d[6].b = 0; + e = 0; + c = 0; +} + +int +main () +{ + foo (); + if (e != 0) + __builtin_abort (); + return 0; +}
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