tests/fixedbugs: regression test for issue 100 (#129)

Adds a regression test based on klauspost/compress#186. This necessitated some related changes:

* Mark "RET" as a terminal instruction
* printer refactor to maintain compatibility with asmfmt
* Tweaks to other regression tests to ensure they are run correctly in CI

Updates #100 #65 #8

printer/goasm.go

@@ -1,10 +1,8 @@
 package printer
 
 import (
-	"fmt"
 	"strconv"
 	"strings"
-	"text/tabwriter"
 
 	"github.com/mmcloughlin/avo/internal/prnt"
 	"github.com/mmcloughlin/avo/ir"
@@ -17,6 +15,9 @@ const dot = "\u00b7"
 type goasm struct {
 	cfg Config
 	prnt.Generator
+
+	instructions []*ir.Instruction
+	clear        bool
 }
 
 // NewGoAsm constructs a printer for writing Go assembly files.
@@ -87,31 +88,21 @@ func (p *goasm) function(f *ir.Function) {
 	}
 	p.Printf(", %s\n", textsize(f))
 
-	w := p.tabwriter()
-	clear := true
-	flush := func() {
-		w.Flush()
-		w = p.tabwriter()
-		if !clear {
-			p.NL()
-			clear = true
-		}
-	}
+	p.clear = true
 	for _, node := range f.Nodes {
 		switch n := node.(type) {
 		case *ir.Instruction:
-			leader := []byte{tabwriter.Escape, '\t', tabwriter.Escape}
-			fmt.Fprint(w, string(leader)+n.Opcode)
-			if len(n.Operands) > 0 {
-				fmt.Fprintf(w, "\t%s", joinOperands(n.Operands))
+			p.instruction(n)
+			if n.IsTerminal || n.IsUnconditionalBranch() {
+				p.flush()
 			}
-			fmt.Fprint(w, "\n")
-			clear = false
 		case ir.Label:
-			flush()
+			p.flush()
+			p.ensureclear()
 			p.Printf("%s:\n", n)
 		case *ir.Comment:
-			flush()
+			p.flush()
+			p.ensureclear()
 			for _, line := range n.Lines {
 				p.Printf("\t// %s\n", line)
 			}
@@ -119,11 +110,45 @@ func (p *goasm) function(f *ir.Function) {
 			panic("unexpected node type")
 		}
 	}
-	w.Flush()
+	p.flush()
 }
 
-func (p *goasm) tabwriter() *tabwriter.Writer {
-	return tabwriter.NewWriter(p.Raw(), 4, 4, 1, ' ', tabwriter.StripEscape)
+func (p *goasm) instruction(i *ir.Instruction) {
+	p.instructions = append(p.instructions, i)
+	p.clear = false
+}
+
+func (p *goasm) flush() {
+	if len(p.instructions) == 0 {
+		return
+	}
+
+	// Determine instruction width. Instructions with no operands are not
+	// considered in this calculation.
+	width := 0
+	for _, i := range p.instructions {
+		if len(i.Operands) > 0 && len(i.Opcode) > width {
+			width = len(i.Opcode)
+		}
+	}
+
+	// Output instruction block.
+	for _, i := range p.instructions {
+		if len(i.Operands) > 0 {
+			p.Printf("\t%-*s%s\n", width+1, i.Opcode, joinOperands(i.Operands))
+		} else {
+			p.Printf("\t%s\n", i.Opcode)
+		}
+	}
+
+	p.instructions = nil
+}
+
+func (p *goasm) ensureclear() {
+	if !p.clear {
+		p.NL()
+		p.clear = true
+	}
 }
 
 func (p *goasm) global(g *ir.Global) {

printer/goasm_test.go

@@ -81,3 +81,27 @@ func TestConstraints(t *testing.T) {
 		"",
 	})
 }
+
+func TestAlignmentNoOperands(t *testing.T) {
+	ctx := build.NewContext()
+	ctx.Function("alignment")
+	ctx.SignatureExpr("func()")
+	ctx.ADDQ(reg.RAX, reg.RBX)
+	ctx.VMOVDQU(reg.Y4, reg.Y11)
+	ctx.VZEROUPPER()
+	ctx.ADDQ(reg.R9, reg.R13)
+	ctx.RET()
+
+	AssertPrintsLines(t, ctx, printer.NewGoAsm, []string{
+		"// Code generated by avo. DO NOT EDIT.",
+		"",
+		"// func alignment()",
+		"TEXT ·alignment(SB), $0",
+		"\tADDQ    AX, BX",
+		"\tVMOVDQU Y4, Y11",
+		"\tVZEROUPPER",      // instruction with no alignment doesn't affect width
+		"\tADDQ    R9, R13", // retains alignment from above
+		"\tRET",
+		"",
+	})
+}