feat(asm): the immediate multiply and arm64 indirect branches GOROOT writes

Assisted-by: GLM 5.3 Flash

asm/arm64_assemble.go

@@ -637,6 +637,20 @@ func encodeARM64Branch(mnem string, ops []*ast.Operand, pc int, offsets map[stri
 		return a64wordLE(a64UncondBranch(opc, uint32(rn), 0)), nil
 	}
 
+	// The bare spelling BL R9 is the same indirect branch: the parser reads
+	// a bare identifier as a symbol, and one named for a register is an
+	// indirect branch through it, which the toolchain accepts alongside the
+	// parenthesised form (BL (R3) and BL R3 both encode BLR R3).
+	if op.Addr.Sym != nil && op.Addr.Sym.Pseudo == "" && op.Addr.Base == "" && op.Addr.Index == "" {
+		if rn := arm64RegNum(op.Addr.Sym.Name); rn >= 0 {
+			opc := uint32(0) // BR
+			if link {
+				opc = 1 // BLR
+			}
+			return a64wordLE(a64UncondBranch(opc, uint32(rn), 0)), nil
+		}
+	}
+
 	// Symbol reference: BL sym(SB), or B sym(SB) for a tail call, against a
 	// relocation (R_CALLARM64 either way).
 	if op.Addr.Sym != nil && op.Addr.Sym.Pseudo == "SB" {
@@ -1454,6 +1468,15 @@ func encodeARM64Mov(instr *ast.Instr, mnem string, wb string, fi arm64FrameInfo,
 			}
 			return encodeARM64SBAddr(src.Imm.Sym, rd, relocs), nil
 		}
+		// Immediate → memory: only storing zero is encodable (the ZR
+		// register); the toolchain rejects any other immediate-to-memory
+		// combination ("illegal combination").
+		if isMemOperand(dst) {
+			if arm64Imm64(src) != 0 {
+				return nil, fmt.Errorf("%s: illegal combination: an immediate store must be zero", mnem)
+			}
+			return encodeARM64MemOp(mnem, dst, 31, false, fi, "")
+		}
 		rd := arm64RegNum(operandRegName(dst))
 		if rd < 0 {
 			return nil, fmt.Errorf("%s $imm: invalid destination register", mnem)