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[PATCH 3/5] [RISC-V] RISC-V Conditional Move costing [was:Generate Zi…
…cond instruction for select pattern with condition eq or neq to 0] This provides some basic costing to conditional moves. The underlying primitive of an IF-THEN-ELSE which turns into czero is a single insn (COSTS_N_INSNS (1)). But these insns were still consistently showing up with the wrong cost (8 instead of 4). This was chased down to computing the cost of the destination and the cost of the source independently, then summing them. That seems horribly wrong for register destinations. So this patch special cases an INSN that is just a SET of a register destination so that the cost comes from the SET_SRC. Long term the whole costing model needs a review. gcc/ * config/riscv/riscv.cc (riscv_rtx_costs, case IF_THEN_ELSE): Add Zicond costing. (case SET): For INSNs that just set a REG, take the cost from the SET_SRC. Co-authored-by: Jeff Law <jlaw@ventanamicro.com>
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