Large local arrays that are initialized to constant values, gcc uses a static
template and a call to
memcpy. If these arrays are all or mostly zeroes, if we clear the array using
memset and then initialize
the non-zero values inline, it is generally better in two ways:
a) it is faster
b) it requires less program memory overhead to store the array of initializers
Here is an example of source code that gcc could do better on:
void bar (char *);
void foo (void)
{
char bigarray[0x1000] = { 0 };
bar (&bigarray[0]);
}
Which generates a 0x1000 byte constant array of zeroes. Instead, it would be
nice if gcc would just
memset the region to zeroes.
This construct is used extensively in the FAAD2 open source AAC encoder/decoder
library, resulting in
a 35%+ increase in size.
AFAICT, this applies to all targets, not just ARM.
--
Summary: Improve initialization of sparse local arrays
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: jconner at apple dot com
CC: gcc-bugs at gcc dot gnu dot org
GCC host triplet: powerpc-apple-darwin7.9.0
GCC target triplet: arm-none-elf
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21478
