GCC 4.x tree optimization decides to put int values into long long int
temporaries. When RTL expansion comes around, the expander sees only a DImode
multiply and so generates three SImode multiplies to deal with the problem.
GCC 3.x sees that the source values are SImode and uses mulsidi3 to generate
32x32->64 multiplies, which are much more efficient. It also picks up the
accumulation.
(using -O3 for all compilations)
GCC 3.4 has an 84-byte stack frame, and a body of 372 instructions.
GCC 4.1 has a 1416-byte stack frame, and a body of 1668 instructions.
GCC 4.2 has a 1320-byte stack frame, and a body of 1565 instructions.
--
Summary: 4.1, 4.2 (possibly 4.0?) not using mulsidi3
Product: gcc
Version: 4.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: eplondke at gmail dot com
GCC host triplet: x86_64-suse-linux
GCC target triplet: arm-unkown-elf
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29274
