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From: Nathan Sidwell <nathan@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc/devel/c++-modules] gcc.dg/pr94600-5.c .. -8.c: Align struct t0 explictly, as a type, PR middle-end/94600 Date: Thu, 27 Aug 2020 18:09:01 +0000 (GMT) [thread overview] Message-ID: <20200827180901.880D73870906@sourceware.org> (raw) https://gcc.gnu.org/g:5db1fa9bc69dd58ce2f93dd707d05efcfe89ffa8 commit 5db1fa9bc69dd58ce2f93dd707d05efcfe89ffa8 Author: Hans-Peter Nilsson <hp@axis.com> Date: Thu Aug 13 05:12:23 2020 +0200 gcc.dg/pr94600-5.c .. -8.c: Align struct t0 explictly, as a type, PR middle-end/94600 The bitfield-struct t0 in gcc.dg/pr94600-1.c ..-4.c is assigned to a pointer that is a (volatile-and-pointer-)cast literal, so gcc doesn't need to be otherwise told that the address is aligned. But, variants pr94600-5.c ..-8.c are assigned through a "volatile t0 *", and rely on the *type* being naturally aligned, or that the machine has non-strict-alignment moves. Unfortunately, systems exist (for some definitions of exist) where such structs aren't always naturally aligned, for example if it contains only (small) bitfields, even though the size is a naturally accessible size. Specifically, the mmix-knuth-mmixware port has only *byte* alignment for this struct. (If an int is added to the struct, alignment is promoted.) IOW, a prerequisite of the test is false: the struct doesn't have the same alignment as an integer of the same size. The effect is assignment in byte-size pieces, and the test fails. (For a non-volatile assignment, memcpy is called.) That's easily fixable by defining the type as having a specific alignment. This is also closer to the type in the original code, and also as the first variants aren't affected, no second thought or re-visit of pre-fixed compiler is needed. I don't plan to back-port this to gcc-10 branch however. I did sanity-check that the tests still pass on ppc64le-linux. gcc/testsuite: PR middle-end/94600 * gcc.dg/pr94600-5.c, gcc.dg/pr94600-6.c, gcc.dg/pr94600-7.c, gcc.dg/pr94600-8.c: Align t0 to 4-byte boundary. Diff: --- gcc/testsuite/gcc.dg/pr94600-5.c | 2 +- gcc/testsuite/gcc.dg/pr94600-6.c | 2 +- gcc/testsuite/gcc.dg/pr94600-7.c | 2 +- gcc/testsuite/gcc.dg/pr94600-8.c | 2 +- 4 files changed, 4 insertions(+), 4 deletions(-) diff --git a/gcc/testsuite/gcc.dg/pr94600-5.c b/gcc/testsuite/gcc.dg/pr94600-5.c index 90085b3b1df..3be0249273e 100644 --- a/gcc/testsuite/gcc.dg/pr94600-5.c +++ b/gcc/testsuite/gcc.dg/pr94600-5.c @@ -9,7 +9,7 @@ typedef struct { unsigned int f1 : 11; unsigned int f2 : 10; unsigned int f3 : 7; -} t0; +} t0 __attribute__((__aligned__(4))); static t0 a0[] = { { .f0 = 7, .f1 = 99, .f3 = 1, }, diff --git a/gcc/testsuite/gcc.dg/pr94600-6.c b/gcc/testsuite/gcc.dg/pr94600-6.c index 23a81a01f49..c247afef11a 100644 --- a/gcc/testsuite/gcc.dg/pr94600-6.c +++ b/gcc/testsuite/gcc.dg/pr94600-6.c @@ -9,7 +9,7 @@ typedef struct { unsigned int f1 : 11; unsigned int f2 : 10; unsigned int f3 : 7; -} t0; +} t0 __attribute__((__aligned__(4))); void bar(volatile t0 *b) diff --git a/gcc/testsuite/gcc.dg/pr94600-7.c b/gcc/testsuite/gcc.dg/pr94600-7.c index 2f5c759d3a1..81c5231e44c 100644 --- a/gcc/testsuite/gcc.dg/pr94600-7.c +++ b/gcc/testsuite/gcc.dg/pr94600-7.c @@ -9,7 +9,7 @@ typedef struct { unsigned int f1 : 11; unsigned int f2 : 10; unsigned int f3 : 7; -} t0; +} t0 __attribute__((__aligned__(4))); static t0 a0[] = { { .f0 = 7, .f1 = 99, .f3 = 1, }, diff --git a/gcc/testsuite/gcc.dg/pr94600-8.c b/gcc/testsuite/gcc.dg/pr94600-8.c index ded814b3b95..201b2add4d9 100644 --- a/gcc/testsuite/gcc.dg/pr94600-8.c +++ b/gcc/testsuite/gcc.dg/pr94600-8.c @@ -9,7 +9,7 @@ typedef struct { unsigned int f1 : 11; unsigned int f2 : 10; unsigned int f3 : 7; -} t0; +} t0 __attribute__((__aligned__(4))); void bar(volatile t0 *b)
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