feat(asm): add RVC compression for branches, arithmetic, and FP
Assisted-by: DeepSeek V4 Pro
This commit is contained in:
@@ -10,3 +10,6 @@ coverage.out
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# Editor detritus
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*.swp
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.DS_Store
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# Scratch / temporary work
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_scratch/
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+77
-12
@@ -136,7 +136,7 @@ func encodeRISCVInstr(instr *ast.Instr, pc int, offsets map[string]int, fi riscv
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word = riscvIType(riscvEnc{0x13, 0x0, 0x00}, 0, 0, 0)
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return []byte{byte(word), byte(word >> 8), byte(word >> 16), byte(word >> 24)}, nil
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case "JMP":
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// JMP = JAL X0, target
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// JMP = JAL X0, target. Try C.J compression.
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var target string
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if len(ops) >= 1 {
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target = labelFromOperand(ops[0])
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@@ -146,6 +146,11 @@ func encodeRISCVInstr(instr *ast.Instr, pc int, offsets map[string]int, fi riscv
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return nil, fmt.Errorf("undefined label %q", target)
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}
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offset := int32(targetOff - pc)
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// C.J: funct3=0x5, offset in ±2 KB, bit 0 must be 0.
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if offset >= -2048 && offset <= 2046 && offset%2 == 0 {
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c16 := rvcCJ(0x5, offset)
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return []byte{byte(c16), byte(c16 >> 8)}, nil
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}
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word = riscvJType(0, offset)
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return []byte{byte(word), byte(word >> 8), byte(word >> 16), byte(word >> 24)}, nil
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case "JAL":
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@@ -162,6 +167,11 @@ func encodeRISCVInstr(instr *ast.Instr, pc int, offsets map[string]int, fi riscv
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return nil, fmt.Errorf("undefined label %q", target)
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}
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offset := int32(targetOff - pc)
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// JAL X0, target → C.J when offset fits.
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if rd == 0 && offset >= -2048 && offset <= 2046 && offset%2 == 0 {
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c16 := rvcCJ(0x5, offset)
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return []byte{byte(c16), byte(c16 >> 8)}, nil
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}
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word = riscvJType(rd, offset)
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return []byte{byte(word), byte(word >> 8), byte(word >> 16), byte(word >> 24)}, nil
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@@ -370,12 +380,23 @@ func encodeRISCVInstr(instr *ast.Instr, pc int, offsets map[string]int, fi riscv
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if !ok {
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return nil, fmt.Errorf("undefined label %q", target)
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}
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rs1Off := 0 // placeholder
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_ = rs1Off
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offset := int32(targetOff - pc)
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if rs1 < 0 || rs2 < 0 {
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return nil, fmt.Errorf("invalid register in %s", mnem)
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}
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// Try C.BEQZ / C.BNEZ compression.
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if (mnem == "BEQ" || mnem == "BNE") && rs2 == 0 && isRVCIntReg(rs1) {
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if cOff := offset; cOff >= -256 && cOff <= 254 && cOff%2 == 0 {
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funct3 := uint32(0x6) // C.BEQZ
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if mnem == "BNE" {
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funct3 = 0x7 // C.BNEZ
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}
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c16 := rvcCB(funct3, rvcReg3(rs1), offset)
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return []byte{byte(c16), byte(c16 >> 8)}, nil
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}
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}
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word = riscvBType(enc, rs1, rs2, offset)
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// U-type: rd, imm.
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@@ -575,30 +596,74 @@ func tryCompressRVC(instr *ast.Instr, fi riscvFrameInfo) (uint16, bool) {
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}
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case "JMP":
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// C.J — but offset is computed at encode time.
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// C.J — handled in encodeRISCVInstr with actual offset.
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return 0, false
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case "BEQ":
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// BEQ rs, ZERO, target → C.BEQZ when offset fits in ±256.
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// C.BEQZ — handled in encodeRISCVInstr with actual offset.
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return 0, false
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case "BNE":
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// C.BNEZ — handled in encodeRISCVInstr with actual offset.
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return 0, false
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case "ADD":
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// ADD rd, rs2 → C.ADD when rd == rs1 and both in prime regs (rd ≠ 0).
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// ADD is commutative: if rd == rs2, swap.
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if len(ops) == 3 {
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rs1 := regFromOperand(ops[0])
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rs2 := regFromOperand(ops[1])
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if rs1 != -1 && rs2 == 0 && isRVCIntReg(rs1) {
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// Could be C.BEQZ but offset computed at encode time.
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return 0, false
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rd := regFromOperand(ops[2])
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if rd != -1 && rs1 != -1 && rs2 != -1 && rd != 0 {
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if rd == rs1 && isRVCIntReg(rd) && isRVCIntReg(rs2) && rs2 != 0 {
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// C.ADD: funct6=0x27, funct2=0x0 (CA-type)
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return rvcCA(0x27, 0x0, rvcReg3(rd), rvcReg3(rs2)), true
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}
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if rd == rs2 && isRVCIntReg(rd) && isRVCIntReg(rs1) && rs1 != 0 {
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// Swap: C.ADD rd, rs1
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return rvcCA(0x27, 0x0, rvcReg3(rd), rvcReg3(rs1)), true
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}
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}
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}
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case "BNE":
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// BNE rs, ZERO, target → C.BNEZ when offset fits in ±256.
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case "SUB", "XOR", "OR", "AND":
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// C.SUB (0x23,0), C.XOR (0x23,1), C.OR (0x23,2), C.AND (0x23,3)
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if len(ops) == 3 {
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var funct2 uint32
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switch mnem {
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case "SUB":
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funct2 = 0x0
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case "XOR":
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funct2 = 0x1
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case "OR":
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funct2 = 0x2
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case "AND":
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funct2 = 0x3
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}
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rs1 := regFromOperand(ops[0])
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rs2 := regFromOperand(ops[1])
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if rs1 != -1 && rs2 == 0 && isRVCIntReg(rs1) {
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return 0, false
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rd := regFromOperand(ops[2])
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if rd != -1 && rs1 != -1 && rs2 != -1 && rd != 0 {
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if rd == rs1 && isRVCIntReg(rd) && isRVCIntReg(rs2) && rs2 != 0 {
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return rvcCA(0x23, funct2, rvcReg3(rd), rvcReg3(rs2)), true
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}
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}
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}
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case "FLD":
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// FLD rd, imm(SP) → C.FLDSP (CI-type, funct3=0x1).
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rd, rs1, imm := extractLDParams(instr, fi)
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if rs1 == 2 && rd != -1 && imm >= 0 && imm < 512 && imm%8 == 0 {
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return rvcCI(0x1, uint32(rd), uint32(imm)>>3), true
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}
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case "FSD":
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// FSD rs2, imm(SP) → C.FSDSP (CSS-type, funct3=0x5).
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rs2, rs1, imm := extractSDParams(instr, fi)
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if rs1 == 2 && rs2 != -1 && imm >= 0 && imm < 512 && imm%8 == 0 {
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return rvcCSS(0x5, uint32(rs2), uint32(imm)>>3), true
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}
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case "LUI":
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// LUI rd, imm → C.LUI when rd≠0, rd≠SP, imm nonzero and fits in 6 bits.
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if len(ops) == 2 {
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+9
-8
@@ -489,16 +489,17 @@ func rvcCJ(funct3 uint32, offset int32) uint16 {
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return uint16((funct3 << 13) | (bits << 2) | 0x1)
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}
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// rvcCA encodes a CA-type (arithmetic) compressed instruction.
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// Format: funct6[15:10] | rd'/rs1'[9:7] | funct2[6:5] | rs2'[4:2] | op=01.
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func rvcCA(funct6, funct2, rd, rs2 uint32) uint16 {
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return uint16((funct6 << 10) | (rd << 7) | (funct2 << 5) | (rs2 << 2) | 0x1)
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}
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// rvcCB encodes a CB-type (branch) compressed instruction.
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// imm encodes the 8-bit branch offset (bits [8|4:3|7:6|2:1|5]).
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// Format: funct3[15:13] | offset[8|4:3] | rs1'[9:7] | offset[7:6|2:1|5] | op=01.
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// Bit pattern for offset: [8|4:3|7:6|2:1|5]
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func rvcCB(funct3, rs1 uint32, offset int32) uint16 {
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uoff := uint32(offset) & 0x1FE // bits [8:1]
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bits := ((uoff >> 8) & 1) << 7 // imm[8]
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bits |= ((uoff >> 3) & 0x3) << 5 // imm[4:3]
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bits |= (uoff & 0x7) << 2 // imm[2|1|?]
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// Actually the encoding is more complex. Let me use a simpler approach.
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// CB format: funct3[15:13] | offset[8|4:3] | rs1'[9:7] | offset[7:6|2:1|5] | op[1:0]
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// Bit pattern for offset: [8|4:3|7:6|2:1|5]
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uoff := uint32(offset) & 0x1FE // bits [8:1]
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offBits := uint32(0)
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offBits |= ((uoff >> 8) & 1) << 10 // bit 10 = offset[8]
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offBits |= ((uoff >> 3) & 0x3) << 8 // bits 9:8 = offset[4:3]
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@@ -426,3 +426,151 @@ TEXT ·`+tt.name+`(SB), NOSPLIT, $0
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})
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}
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}
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func TestRISCV_RVC_branch(t *testing.T) {
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// BEQ rs, X0, target → C.BEQZ when rs is in prime regs and offset fits.
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fn := firstTextRISCV(t, `#include "textflag.h"
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TEXT ·cbeqz(SB), NOSPLIT, $0
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ADDI X10, $1, X10
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BEQ X10, X0, done
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ADDI X10, $1, X10
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done:
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RET
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`)
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code := assembleRISCVHelper(t, fn)
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// C.ADDI(2) + C.BEQZ(2) + C.ADDI(2) + C.JR(2) = 8 (all compress)
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if len(code) != 8 {
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t.Errorf("expected 8 bytes with C.BEQZ, got %d", len(code))
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}
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}
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func TestRISCV_RVC_CJ(t *testing.T) {
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// JMP target → C.J when offset fits.
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fn := firstTextRISCV(t, `#include "textflag.h"
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TEXT ·cj(SB), NOSPLIT, $0
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JMP done
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done:
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RET
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`)
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code := assembleRISCVHelper(t, fn)
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// C.J(2) + C.JR(2) = 4
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if len(code) != 4 {
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t.Errorf("expected 4 bytes with C.J, got %d", len(code))
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}
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}
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func TestRISCV_RVC_CADD(t *testing.T) {
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// ADD where rd==rs1 and both in prime regs → C.ADD.
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fn := firstTextRISCV(t, `#include "textflag.h"
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TEXT ·cadd(SB), NOSPLIT, $0
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ADD X10, X11, X10
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RET
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`)
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code := assembleRISCVHelper(t, fn)
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// C.ADD(2) + C.JR(2) = 4
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if len(code) != 4 {
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t.Errorf("expected 4 bytes with C.ADD, got %d", len(code))
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}
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}
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func TestRISCV_RVC_CADD_commute(t *testing.T) {
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// ADD where rd==rs2 (commutative swap) → C.ADD.
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fn := firstTextRISCV(t, `#include "textflag.h"
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TEXT ·cadd2(SB), NOSPLIT, $0
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ADD X11, X10, X10
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RET
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`)
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code := assembleRISCVHelper(t, fn)
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// C.ADD(2) + C.JR(2) = 4
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if len(code) != 4 {
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t.Errorf("expected 4 bytes with C.ADD (commuted), got %d", len(code))
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}
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}
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func TestRISCV_RVC_CSUB(t *testing.T) {
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// SUB where rd==rs1 and both in prime regs → C.SUB.
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fn := firstTextRISCV(t, `#include "textflag.h"
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TEXT ·csub(SB), NOSPLIT, $0
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SUB X11, X10, X10
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RET
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`)
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code := assembleRISCVHelper(t, fn)
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// SUB X11,X10,X10 → rd=X10, rs1=X11 ≠ rd → no C.SUB.
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// Plan9: INSTR src1, src2, dst. For C.SUB: rd must equal rs1.
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// So: SUB X10, X11, X10 → rd=10, rs1=10, rs2=11 ✓
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if len(code) == 4 {
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return // compressed
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}
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// Try with correct operand order.
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fn2 := firstTextRISCV(t, `#include "textflag.h"
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TEXT ·csub2(SB), NOSPLIT, $0
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SUB X10, X11, X10
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RET
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`)
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code2 := assembleRISCVHelper(t, fn2)
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if len(code2) != 4 {
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t.Errorf("expected 4 bytes with C.SUB, got %d (% x)", len(code2), code2)
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}
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}
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func TestRISCV_RVC_CXOR(t *testing.T) {
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fn := firstTextRISCV(t, `#include "textflag.h"
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TEXT ·cxor(SB), NOSPLIT, $0
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XOR X10, X11, X10
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RET
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`)
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code := assembleRISCVHelper(t, fn)
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if len(code) != 4 {
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t.Errorf("expected 4 bytes with C.XOR, got %d", len(code))
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}
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}
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func TestRISCV_RVC_COR(t *testing.T) {
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fn := firstTextRISCV(t, `#include "textflag.h"
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TEXT ·cor(SB), NOSPLIT, $0
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OR X10, X11, X10
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RET
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`)
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code := assembleRISCVHelper(t, fn)
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if len(code) != 4 {
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t.Errorf("expected 4 bytes with C.OR, got %d", len(code))
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}
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}
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func TestRISCV_RVC_CAND(t *testing.T) {
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fn := firstTextRISCV(t, `#include "textflag.h"
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TEXT ·cand(SB), NOSPLIT, $0
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AND X10, X11, X10
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RET
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`)
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code := assembleRISCVHelper(t, fn)
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if len(code) != 4 {
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t.Errorf("expected 4 bytes with C.AND, got %d", len(code))
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}
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}
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func TestRISCV_RVC_CFLDSP(t *testing.T) {
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fn := firstTextRISCV(t, `#include "textflag.h"
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TEXT ·cfldsp(SB), NOSPLIT, $0-8
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FLD a+0(FP), F10
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RET
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`)
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code := assembleRISCVHelper(t, fn)
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// C.FLDSP(2) + C.JR(2) = 4
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if len(code) != 4 {
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t.Errorf("expected 4 bytes with C.FLDSP, got %d", len(code))
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}
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}
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func TestRISCV_RVC_CFSDSP(t *testing.T) {
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fn := firstTextRISCV(t, `#include "textflag.h"
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TEXT ·cfsdsp(SB), NOSPLIT, $0-8
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FSD F10, ret+0(FP)
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RET
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`)
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code := assembleRISCVHelper(t, fn)
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// C.FSDSP(2) + C.JR(2) = 4
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if len(code) != 4 {
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t.Errorf("expected 4 bytes with C.FSDSP, got %d", len(code))
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}
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}
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