Strength-reduce multiplication by known constants

a81e17175b498e57b8ed31f044c7508a47e93a13695c0c19c368fe0605f40a1b
Alexis Sellier committed ago 1 parent ebab4823
lib/std/arch/rv64/isel.rad +26 -5
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                encode::subw(rd, rs1, rs2)
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                    if typ == il::Type::W32 else
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                encode::sub(rd, rs1, rs2));
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        }
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        case il::BinOp::Mul => {
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            let rs2 = resolveVal(s, super::SCRATCH2, b);
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            emit::emit(s.e,
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                encode::mulw(rd, rs1, rs2)
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                    if typ == il::Type::W32 else
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                encode::mul(rd, rs1, rs2));
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            // Strength-reduce multiplication by known constants.
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            if let case il::Val::Imm(imm) = b {
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                if imm == 0 {
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                    emit::emit(s.e, encode::mv(rd, super::ZERO));
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                } else if imm == 1 {
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                    emitMv(s, rd, rs1);
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                } else if imm == 2 {
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                    emit::emit(s.e, encode::slli(rd, rs1, 1));
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                } else if imm == 4 {
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                    emit::emit(s.e, encode::slli(rd, rs1, 2));
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                } else if imm == 8 {
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                    emit::emit(s.e, encode::slli(rd, rs1, 3));
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                } else {
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                    let rs2 = resolveVal(s, super::SCRATCH2, b);
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                    emit::emit(s.e,
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                        encode::mulw(rd, rs1, rs2)
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                            if typ == il::Type::W32 else
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                        encode::mul(rd, rs1, rs2));
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                }
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            } else {
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                let rs2 = resolveVal(s, super::SCRATCH2, b);
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                emit::emit(s.e,
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                    encode::mulw(rd, rs1, rs2)
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                        if typ == il::Type::W32 else
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                    encode::mul(rd, rs1, rs2));
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            }
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        }
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        case il::BinOp::Sdiv => {
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            let rs2 = resolveVal(s, super::SCRATCH2, b);
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            emitTrapIfZero(s, rs2);
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            emit::emit(s.e,