https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65069
Bug ID: 65069
Summary: [SH] Calculate constants
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: olegendo at gcc dot gnu.org
Target: sh*-*-*
If constants don't fit into K08 or I08 they are usually placed into the
constant pool and loaded using a PC-relative load. Some constants however can
be calculated with 2..3 arithmetic insns. This can be beneficial in some
cases:
- If the constant load is required only once, it can result in shorter code. A
load of a full 32 bit constant is 2 + 4 = 6 bytes, which is 3 insns worth. For
instance loading 0x00FFFFFF can be done by 'mov #-1,rn; shlr8 rn;'.
- On MCUs that don't separate memories/paths for instruction and data, memory
loads conflict with instruction fetches. Thus 2 insns that don't access memory
might be faster than 1 mem load insn.
