radiance · commit

rv64: Skip zero chunks in wide immediates

9a9ad0762d09613b4059c17feee15b235ee0741eb40ad12e1c9e52a91034a3a8

Emit an ADDI for each low-bit chunk only when the chunk is nonzero.
Keep all shifts and signed upper-half loading so full-width values
remain correct while sparse constants need fewer target instructions.

Assisted-by: Codex:gpt-6-astra

Alexis Sellier committed 15 days ago 1 parent 587e7cb3

lib/std/arch/rv64/emit.rad +12 -3


    // Load upper 32 bits.
    loadImm(e, rd, hi32 as i64);
    // Shift left by 11, add bits [31:21].
    emit(e, encode::slli(rd, rd, 11));
    emit(e, encode::addi(rd, rd, (lower >> 21) & 0x7FF));
    let chunkHi = (lower >> 21) & 0x7FF;
    if chunkHi <> 0 {
        emit(e, encode::addi(rd, rd, chunkHi));
    }
    // Shift left by 11, add bits [20:10].
    emit(e, encode::slli(rd, rd, 11));
    emit(e, encode::addi(rd, rd, (lower >> 10) & 0x7FF));
    let chunkMid = (lower >> 10) & 0x7FF;
    if chunkMid <> 0 {
        emit(e, encode::addi(rd, rd, chunkMid));
    }
    // Shift left by 10, add bits [9:0].
    emit(e, encode::slli(rd, rd, 10));
    emit(e, encode::addi(rd, rd, lower & 0x3FF));
    let chunkLo = lower & 0x3FF;
    if chunkLo <> 0 {
        emit(e, encode::addi(rd, rd, chunkLo));
    }
}

/// Emit add-immediate, handling large immediates.
export fn emitAddImm(e: *mut Emitter, rd: gen::Reg, rs: gen::Reg, imm: i32) {
    if imm >= super::MIN_IMM and imm <= super::MAX_IMM {

524	524
525	525		// Load upper 32 bits.
526	526		loadImm(e, rd, hi32 as i64);
527	527		// Shift left by 11, add bits [31:21].
528	528		emit(e, encode::slli(rd, rd, 11));
529		-	emit(e, encode::addi(rd, rd, (lower >> 21) & 0x7FF));
	529	+	let chunkHi = (lower >> 21) & 0x7FF;
	530	+	if chunkHi <> 0 {
	531	+	emit(e, encode::addi(rd, rd, chunkHi));
	532	+	}
530	533		// Shift left by 11, add bits [20:10].
531	534		emit(e, encode::slli(rd, rd, 11));
532		-	emit(e, encode::addi(rd, rd, (lower >> 10) & 0x7FF));
	535	+	let chunkMid = (lower >> 10) & 0x7FF;
	536	+	if chunkMid <> 0 {
	537	+	emit(e, encode::addi(rd, rd, chunkMid));
	538	+	}
533	539		// Shift left by 10, add bits [9:0].
534	540		emit(e, encode::slli(rd, rd, 10));
535		-	emit(e, encode::addi(rd, rd, lower & 0x3FF));
	541	+	let chunkLo = lower & 0x3FF;
	542	+	if chunkLo <> 0 {
	543	+	emit(e, encode::addi(rd, rd, chunkLo));
	544	+	}
536	545		}
537	546
538	547		/// Emit add-immediate, handling large immediates.
539	548		export fn emitAddImm(e: *mut Emitter, rd: gen::Reg, rs: gen::Reg, imm: i32) {
540	549		if imm >= super::MIN_IMM and imm <= super::MAX_IMM {