https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64760
Bug ID: 64760 Summary: [SH] Avoid multiple #imm,r0 insns with the same #imm value 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*-*-* In libstdc++ there is code such as: mov r9,r0 cmp/eq #-1,r0 mov r1,r0 movt r2 cmp/eq #-1,r0 movt r1 cmp/eq r1,r2 bt ... It seems that it's better to avoid #imm,r0 insns such as cmp/eq, and, or, xor, tst, if the #imm value can be shared among several insns. The insns don't have to be same, only the constant value. The above code could be something like: mov #-1,r0 cmp/eq r9,r0 movt r2 cmp/eq r1,r0 movt r1 cmp/eq r1,r2 Preferably, this should be done before RA to reduce r0 pressure. It can be accomplished by simply loading the constant into a pseudo and replacing the operands in the insns. On the other hand, if the other operand (other than #imm) is likely to end up in r0, the #imm,r0 insn is probably going to be better. A possible metric for 'likely to be in r0' could be: - the operand is loaded using a mov.{b|w} @(disp,Rn),R0 - the operand is needed in r0 by some other surrounding insns