feat(asm): byte-identical go-flac AVX2 assembly with scalar families and jump relaxation

Assisted-by: Qwen 3.8 Max Preview

parser/parser_test.go

@@ -34,6 +34,46 @@ func texts(f *ast.File) []*ast.Text {
 	return out
 }
 
+// TestNegativeDisplacement is a regression test for a leading negative
+// displacement with a base and index: the sign pushed the parenthesis one
+// token further out than the lookahead expected, and the whole address used
+// to parse empty.
+func TestNegativeDisplacement(t *testing.T) {
+	f, errs := Parse("neg_amd64.s", `
+#include "textflag.h"
+TEXT ·f(SB), NOSPLIT, $0
+	LEAQ -4(DX)(R9*4), R9
+	MOVQ +8(AX), BX
+	RET
+`)
+	if len(errs) > 0 {
+		t.Fatalf("parse: %v", errs)
+	}
+	fn := texts(f)[0]
+	var leaq, movq *ast.Instr
+	for _, s := range fn.Body {
+		if in, ok := s.(*ast.Instr); ok {
+			switch in.Mnemonic.Text {
+			case "LEAQ":
+				leaq = in
+			case "MOVQ":
+				movq = in
+			}
+		}
+	}
+	if leaq == nil || movq == nil {
+		t.Fatalf("instructions not parsed: leaq=%v movq=%v", leaq, movq)
+	}
+	a := leaq.Operands[0].Addr
+	if a.Base != "DX" || a.Index != "R9" || a.Scale != 4 || a.Offset != -4 || !a.HasOff {
+		t.Errorf("LEAQ addr = %+v, want -4(DX)(R9*4)", a)
+	}
+	b := movq.Operands[0].Addr
+	if b.Base != "AX" || b.Offset != 8 || !b.HasOff {
+		t.Errorf("MOVQ addr = %+v, want +8(AX)", b)
+	}
+}
+
 func TestParseSample(t *testing.T) {
 	f := mustParse(t, "../testdata/sample_amd64.s")