Hi! The following testcase is miscompiled, because there is a buffer overflow in push_partial_def in the little-endian case when working 64-byte vectors. The code computes the number of bytes we need in the BUFFER: NEEDED_LEN, which is rounded up number of bits we need. Then the code native_encode_expr each (partially overlapping) pd into THIS_BUFFER. If pd.offset < 0, i.e. the pd.rhs store starts at some bits before the window we are interested in, we pass -pd.offset to native_encode_expr and shrink the size already earlier: HOST_WIDE_INT size = pd.size; if (pd.offset < 0) size -= ROUND_DOWN (-pd.offset, BITS_PER_UNIT); On this testcase, the problem is with a store with pd.offset > 0, in particular pd.offset 256, pd.size 512, i.e. a 64-byte store which doesn't fit into entirely into BUFFER. We have just: size = MIN (size, (HOST_WIDE_INT) needed_len * BITS_PER_UNIT); in this case for little-endian, which isn't sufficient, because needed_len is 64, the entire BUFFER (except of the last extra byte used for shifting). native_encode_expr fills the whole THIS_BUFFER (again, except the last extra byte), and the code then performs memcpy (BUFFER + 32, THIS_BUFFER, 64); which overflows BUFFER and as THIS_BUFFER is usually laid out after it, overflows it into THIS_BUFFER. The following patch fixes it by for pd.offset > 0 making sure size is reduced too. For big-endian the code does things differently and already handles this right.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2020-03-25 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/94300 * tree-ssa-sccvn.c (vn_walk_cb_data::push_partial_def): If pd.offset is positive, make sure that off + size isn't larger than needed_len. * gcc.target/i386/avx512f-pr94300.c: New test. --- gcc/tree-ssa-sccvn.c.jj 2020-03-12 14:28:13.365363769 +0100 +++ gcc/tree-ssa-sccvn.c 2020-03-24 15:48:22.465737253 +0100 @@ -2058,6 +2058,8 @@ vn_walk_cb_data::push_partial_def (pd_da shift_bytes_in_array_left (this_buffer, len + 1, amnt); unsigned int off = pd.offset / BITS_PER_UNIT; gcc_assert (off < needed_len); + size = MIN (size, + (HOST_WIDE_INT) (needed_len - off) * BITS_PER_UNIT); p = buffer + off; if (amnt + size < BITS_PER_UNIT) { --- gcc/testsuite/gcc.target/i386/avx512f-pr94300.c.jj 2020-03-24 15:38:32.391643991 +0100 +++ gcc/testsuite/gcc.target/i386/avx512f-pr94300.c 2020-03-24 15:39:09.874078217 +0100 @@ -0,0 +1,21 @@ +/* PR tree-optimization/94300 */ +/* { dg-do run { target { avx512f } } } */ +/* { dg-options "-O1 -mavx512f -mprefer-vector-width=512 -mtune=skylake-avx512" } */ + +#include "avx512f-check.h" + +typedef double V __attribute__((vector_size (64))); + +static void +avx512f_test (void) +{ + double mem[16]; + const V a = { 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0 }; + const V b = { 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0 }; + V c; + __builtin_memcpy (mem, &a, 64); + __builtin_memcpy (mem + 8, &b, 64); + __builtin_memcpy (&c, mem + 4, 64); + if (c[5] != 9.0) + __builtin_abort (); +} Jakub