feat(riscv64,loong64): operand tail, float DATA and honest port classification

Assisted-by: GLM 5.3 Flash

testdata/verify/bookkeep_riscv64.s

@@ -0,0 +1,40 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Differential kernel for the riscv64 bookkeeping statements and the
+// slot-relative branches: FUNCDATA and PCDATA (the expanded forms of the
+// funcdata.h macros, contributing no bytes), UNDEF (the toolchain's ebreak),
+// and the JMP N(PC) slot jumps including the self-loop and the backward form.
+
+#include "textflag.h"
+
+TEXT ·bookkeep(SB), NOSPLIT, $8-8
+	FUNCDATA $1, marks<>(SB)
+	PCDATA   $1, $-1
+	MOV      ZERO, ret+0(FP)
+	PCDATA   $1, $1
+	UNDEF
+	MOV      $1, X10
+	RET
+
+TEXT ·slots(SB), NOSPLIT, $0-0
+	MOV $1, X10
+	JMP 2(PC)
+	MOV $64, X11
+	MOV $128, X12
+	MOV $2, X11
+	MOV $3, X12
+	BEQ X10, X11, skip
+	JMP -2(PC)
+
+skip:
+	JMP 0(PC)
+
+TEXT ·marksreader(SB), NOSPLIT, $0-8
+	MOV $marks<>(SB), X10
+	MOV (X10), X11
+	MOV X11, ret+0(FP)
+	RET
+
+GLOBL marks<>(SB), RODATA, $8
+DATA marks<>+0(SB)/8, $1234605616436508552

testdata/verify/branch2_loong64.s

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+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Differential kernel for the loong64 two-operand BEQ/BNE spellings the
+// msan trampolines use: BEQ Rj, target compares against R0 (the beqz form).
+
+#include "textflag.h"
+
+TEXT ·branch2(SB), NOSPLIT, $0-8
+	MOVV arg+0(FP), R4
+	BEQ  R4, zero
+	ADDV $1, R4, R4
+
+zero:
+	MOVV $16, R5
+	BNE  R4, done
+	ADDV $2, R4, R4
+
+done:
+	MOVV R4, ret+0(FP)
+	RET

testdata/verify/datainit_loong64.s

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+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Differential kernel for the loong64 DATA value forms the runtime's exp and
+// asm files use: floating-point initialisers stored as IEEE-754 bits and
+// string initialisers zero-padded within their declared width.
+
+#include "textflag.h"
+
+TEXT ·floatbits(SB), NOSPLIT, $0-8
+	MOVV $floats<>(SB), R12
+	MOVD 8(R12), F0
+	MOVD F0, ret+0(FP)
+	RET
+
+TEXT ·stringhead(SB), NOSPLIT, $0-8
+	MOVV $msg<>(SB), R12
+	MOVV (R12), R13
+	MOVV R13, ret+0(FP)
+	RET
+
+GLOBL floats<>(SB), RODATA, $16
+DATA floats<>+0(SB)/8, $0.0
+DATA floats<>+8(SB)/8, $0.5
+
+GLOBL msg<>(SB), RODATA, $20
+DATA msg<>+0(SB)/20, $"call frame too large"

testdata/verify/wideimm_riscv64.s

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+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Differential kernel for the riscv64 wide MOV immediates: the 64-bit
+// constants the toolchain materialises through shifted 32-bit parts or loads
+// from its pooled $i64 data symbols, and the frame-address immediates
+// ($name+off(FP)) lowered to ADDI against the hardware stack pointer.
+
+#include "textflag.h"
+
+TEXT ·poolload(SB), NOSPLIT, $0-16
+	MOV arg+0(FP), X10
+	MOV $0x0101010101010101, X16
+	MUL X10, X16, X17
+	MOV $0x123456789, X18
+	ADD X18, X17, X17
+	MOV X17, ret+8(FP)
+	RET
+
+TEXT ·shiftload(SB), NOSPLIT, $0-16
+	MOV arg+0(FP), X10
+	MOV $0x8000000000000000, X20
+	MOV $0x100000000, X21
+	ADD X21, X20, X20
+	MOV $0x000fffffffffffda, X22
+	XOR X22, X20, X20
+	ADD X20, X10, X10
+	MOV X10, ret+8(FP)
+	RET
+
+TEXT ·frameaddr(SB), NOSPLIT, $32-16
+	MOV $ret+8(FP), X12
+	MOV $scratch+0(FP), X13
+	ADD X12, X13, X13
+	MOV $slot+16(SP), X14
+	SUB X14, X13, X13
+	MOV X13, ret+8(FP)
+	RET
+
+GLOBL scratch<>(SB), NOPTR, $8