mipsisa64-elf-gcc -S -O2 gcc.target/mips/madd-7.c -DNOMIPS16=
does not produce the expected MADD. On long64 ABIs like EABI64, the loop
starts out with an extra extendsidi2 instruction, and although this instruction
gets removed after reload by a "split to nothing", it is still around at
register allocation time.
extendsidi2 does not allow LO operands, so its presence discourages the
register allocator from using LO for the accumulator. The fix is to add a LO
alternative to extendsidi2.
I'm filing this for 4.5 or later; it isn't something we'd fix in 4,4 or
earlier.
--
Summary: MIPS extendsidi2 does not have a LO alternative
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: rsandifo at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38598
