feat(lint): flag table-known instructions the encoder cannot emit

asm/encodable.go

@@ -0,0 +1,89 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: BSD-3-Clause
+
+package asm
+
+import "strings"
+
+// Encodable reports whether the amd64 encoder knows how to encode the
+// mnemonic.  It mirrors the dispatch in (*enc).encode: the fixed-name
+// instructions, conditional jumps, the CMOV/SET condition families, the
+// VEX/EVEX/opmask/gather/scatter vector paths, the legacy SSE tables and the
+// explicit scalar cases.  A mnemonic that parses (is in the architecture
+// table) but is not encodable would otherwise surface only at assembly time,
+// deep inside a build; the linter uses this predicate to flag it at edit
+// time.
+func Encodable(mnemonic string) bool {
+	upper := strings.ToUpper(mnemonic)
+
+	// Fixed-name instructions (no size suffix).
+	switch upper {
+	case "RET", "NOP", "CALL", "JMP":
+		return true
+	}
+	if _, ok := condCode(upper); ok {
+		return true
+	}
+
+	// VEX/EVEX and friends: the trailing B/W/L/Q/D is part of the mnemonic.
+	base, _, err := parseEvexSuffix(upper)
+	if err != nil {
+		return false
+	}
+	if isVex(base) || isEvex(base) || isKOp(base) || isGather(base) || isScatter(base) ||
+		base == "KMOVW" || base == "KMOVQ" {
+		return true
+	}
+
+	// CMOV carries size then condition (CMOVLGT); SET carries the condition
+	// alone (SETNE).
+	if rest, ok := strings.CutPrefix(upper, "CMOV"); ok && len(rest) >= 2 {
+		if _, ok := jccMap[rest[1:]]; ok {
+			return true
+		}
+	}
+	if rest, ok := strings.CutPrefix(upper, "SET"); ok {
+		if _, ok := jccMap[rest]; ok {
+			return true
+		}
+	}
+
+	// Legacy SSE shuffles and packed binaries dispatch on the full name.
+	if _, ok := sseShufTable[upper]; ok {
+		return true
+	}
+	if _, ok := sseBinTable[upper]; ok {
+		return true
+	}
+
+	// The size-suffix split: retry the tables and the scalar switch on the
+	// base.
+	base2, size := splitSize(upper)
+	if size == 0 {
+		size = 8
+	}
+	_ = size
+	if base2 != upper {
+		if _, ok := sseBinTable[base2]; ok {
+			return true
+		}
+	}
+	switch base2 {
+	case "MOV",
+		"ADD", "SUB", "AND", "OR", "XOR", "CMP",
+		"TEST",
+		"LEA",
+		"INC", "DEC", "NEG", "NOT",
+		"SHL", "SHR", "SAR",
+		"IMUL", "IMUL3",
+		"PUSH", "POP",
+		"BSF", "BSR", "LZCNT", "TZCNT", "POPCNT",
+		"BSWAP",
+		"PREFETCHNTA", "PREFETCHT0", "PREFETCHT1", "PREFETCHT2",
+		"MOVBLZX", "MOVBQZX", "MOVWLZX", "MOVWQZX", "MOVWLSX", "MOVLQSX",
+		"CVTSL2SD", "CVTSQ2SD",
+		"MOVOU", "MOVO", "MOVUPS", "MOVAPS", "MOVUPD", "MOVAPD", "MOVSD", "MOVSS":
+		return true
+	}
+	return false
+}