| Message ID | Zysj1WBJrYz8WshJ@tucnak |
|---|---|
| State | New |
| Headers | show |
| Series | store-merging: Don't use sub_byte_op_p mode for empty_ctor_p unless necessary [PR117439] | expand |
On Wed, 6 Nov 2024, Jakub Jelinek wrote: > Hi! > > encode_tree_to_bitpos uses the more expensive sub_byte_op_p mode in which > it has to allocate a buffer and do various extra work like shifting the bits > etc. if bitlen or bitpos aren't multiples of BITS_PER_UNIT, or if bitlen > doesn't have corresponding integer mode. > The last case is explained later in the comments: > /* The native_encode_expr machinery uses TYPE_MODE to determine how many > bytes to write. This means it can write more than > ROUND_UP (bitlen, BITS_PER_UNIT) / BITS_PER_UNIT bytes (for example > write 8 bytes for a bitlen of 40). Skip the bytes that are not within > bitlen and zero out the bits that are not relevant as well (that may > contain a sign bit due to sign-extension). */ > Now, we've later added empty_ctor_p support, either {} CONSTRUCTOR > or {CLOBBER}, which doesn't use native_encode_expr at all, just memset, > so that case doesn't need those fancy games unless bitlen or bitpos > aren't multiples of BITS_PER_UNIT (unlikely, but let's pretend it is > possible). > > The following patch makes us use the fast path even for empty_ctor_p > which occupy full bytes, we can just memset that in the provided buffer and > don't need to XALLOCAVEC another buffer. > > This patch in itself fixes the testcase from the PR (which was about using > huge XALLLOCAVEC), but I want to do some other changes, to be posted in a > next patch. > > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? OK. Thanks, Richard. > 2024-11-06 Jakub Jelinek <jakub@redhat.com> > > PR tree-optimization/117439 > * gimple-ssa-store-merging.cc (encode_tree_to_bitpos): For > empty_ctor_p use !sub_byte_op_p even if bitlen doesn't have an > integral mode. > > --- gcc/gimple-ssa-store-merging.cc.jj 2024-10-25 10:00:29.467767871 +0200 > +++ gcc/gimple-ssa-store-merging.cc 2024-11-04 18:40:14.667260621 +0100 > @@ -1934,14 +1934,15 @@ encode_tree_to_bitpos (tree expr, unsign > unsigned int total_bytes) > { > unsigned int first_byte = bitpos / BITS_PER_UNIT; > - bool sub_byte_op_p = ((bitlen % BITS_PER_UNIT) > - || (bitpos % BITS_PER_UNIT) > - || !int_mode_for_size (bitlen, 0).exists ()); > bool empty_ctor_p > = (TREE_CODE (expr) == CONSTRUCTOR > && CONSTRUCTOR_NELTS (expr) == 0 > && TYPE_SIZE_UNIT (TREE_TYPE (expr)) > - && tree_fits_uhwi_p (TYPE_SIZE_UNIT (TREE_TYPE (expr)))); > + && tree_fits_uhwi_p (TYPE_SIZE_UNIT (TREE_TYPE (expr)))); > + bool sub_byte_op_p = ((bitlen % BITS_PER_UNIT) > + || (bitpos % BITS_PER_UNIT) > + || (!int_mode_for_size (bitlen, 0).exists () > + && !empty_ctor_p)); > > if (!sub_byte_op_p) > { > > Jakub > >
--- gcc/gimple-ssa-store-merging.cc.jj 2024-10-25 10:00:29.467767871 +0200 +++ gcc/gimple-ssa-store-merging.cc 2024-11-04 18:40:14.667260621 +0100 @@ -1934,14 +1934,15 @@ encode_tree_to_bitpos (tree expr, unsign unsigned int total_bytes) { unsigned int first_byte = bitpos / BITS_PER_UNIT; - bool sub_byte_op_p = ((bitlen % BITS_PER_UNIT) - || (bitpos % BITS_PER_UNIT) - || !int_mode_for_size (bitlen, 0).exists ()); bool empty_ctor_p = (TREE_CODE (expr) == CONSTRUCTOR && CONSTRUCTOR_NELTS (expr) == 0 && TYPE_SIZE_UNIT (TREE_TYPE (expr)) - && tree_fits_uhwi_p (TYPE_SIZE_UNIT (TREE_TYPE (expr)))); + && tree_fits_uhwi_p (TYPE_SIZE_UNIT (TREE_TYPE (expr)))); + bool sub_byte_op_p = ((bitlen % BITS_PER_UNIT) + || (bitpos % BITS_PER_UNIT) + || (!int_mode_for_size (bitlen, 0).exists () + && !empty_ctor_p)); if (!sub_byte_op_p) {
Hi! encode_tree_to_bitpos uses the more expensive sub_byte_op_p mode in which it has to allocate a buffer and do various extra work like shifting the bits etc. if bitlen or bitpos aren't multiples of BITS_PER_UNIT, or if bitlen doesn't have corresponding integer mode. The last case is explained later in the comments: /* The native_encode_expr machinery uses TYPE_MODE to determine how many bytes to write. This means it can write more than ROUND_UP (bitlen, BITS_PER_UNIT) / BITS_PER_UNIT bytes (for example write 8 bytes for a bitlen of 40). Skip the bytes that are not within bitlen and zero out the bits that are not relevant as well (that may contain a sign bit due to sign-extension). */ Now, we've later added empty_ctor_p support, either {} CONSTRUCTOR or {CLOBBER}, which doesn't use native_encode_expr at all, just memset, so that case doesn't need those fancy games unless bitlen or bitpos aren't multiples of BITS_PER_UNIT (unlikely, but let's pretend it is possible). The following patch makes us use the fast path even for empty_ctor_p which occupy full bytes, we can just memset that in the provided buffer and don't need to XALLOCAVEC another buffer. This patch in itself fixes the testcase from the PR (which was about using huge XALLLOCAVEC), but I want to do some other changes, to be posted in a next patch. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? 2024-11-06 Jakub Jelinek <jakub@redhat.com> PR tree-optimization/117439 * gimple-ssa-store-merging.cc (encode_tree_to_bitpos): For empty_ctor_p use !sub_byte_op_p even if bitlen doesn't have an integral mode. Jakub