test: in asmcheck, dump only the functions which fail

Before this change, in case of any failure, asmcheck was
dumping to stderr the whole output of compile -S, which
can be very long if it contains multiple functions.

Make it so it filters the output to only display the
assembly output of functions for which at least one opcode
check failed. This greatly simplifies debugging.

Change-Id: I1bbf54473b8252a3384e2c1dade82d926afc119d
Reviewed-on: https://go-review.googlesource.com/98444
Run-TryBot: Giovanni Bajo <rasky@develer.com>
Reviewed-by: Keith Randall <khr@golang.org>

test/run.go

@@ -1294,10 +1294,11 @@ var (
 )
 
 type wantedAsmOpcode struct {
-	line     int
-	opcode   *regexp.Regexp
-	negative bool
-	found    bool
+	fileline string         // original source file/line (eg: "/path/foo.go:45")
+	line     int            // original source line
+	opcode   *regexp.Regexp // opcode check to be performed on assembly output
+	negative bool           // true if the check is supposed to fail rather than pass
+	found    bool           // true if the opcode check matched at least one in the output
 }
 
 func (t *test) wantedAsmOpcodes(fn string) (map[string]map[string][]wantedAsmOpcode, []string) {
@@ -1353,6 +1354,7 @@ func (t *test) wantedAsmOpcodes(fn string) (map[string]map[string][]wantedAsmOpc
 				archs[arch] = true
 				ops[arch][lnum] = append(ops[arch][lnum], wantedAsmOpcode{
 					negative: negative,
+					fileline: lnum,
 					line:     i + 1,
 					opcode:   oprx,
 				})
@@ -1371,28 +1373,46 @@ func (t *test) wantedAsmOpcodes(fn string) (map[string]map[string][]wantedAsmOpc
 }
 
 func (t *test) asmCheck(outStr string, fn string, arch string, fullops map[string][]wantedAsmOpcode) (err error) {
-	defer func() {
-		if *verbose && err != nil {
-			log.Printf("%s gc output:\n%s", t, outStr)
-		}
-	}()
-
+	// The assembly output contains the concatenated dump of multiple functions.
+	// the first line of each function begins at column 0, while the rest is
+	// indented by a tabulation. These data structures help us index the
+	// output by function.
+	functionMarkers := make([]int, 1)
+	lineFuncMap := make(map[string]int)
+
+	lines := strings.Split(outStr, "\n")
 	rxLine := regexp.MustCompile(fmt.Sprintf(`\((%s:\d+)\)\s+(.*)`, regexp.QuoteMeta(fn)))
 
-	for _, line := range strings.Split(outStr, "\n") {
+	for nl, line := range lines {
+		// Check if this line begins a function
+		if len(line) > 0 && line[0] != '\t' {
+			functionMarkers = append(functionMarkers, nl)
+		}
+
+		// Search if this line contains a assembly opcode (which is prefixed by the
+		// original source file/line in parenthesis)
 		matches := rxLine.FindStringSubmatch(line)
 		if len(matches) == 0 {
 			continue
 		}
+		srcFileLine, asm := matches[1], matches[2]
+
+		// Associate the original file/line information to the current
+		// function in the output; it will be useful to dump it in case
+		// of error.
+		lineFuncMap[srcFileLine] = len(functionMarkers) - 1
 
-		ops := fullops[matches[1]]
-		asm := matches[2]
+		// If there are opcode checks associated to this source file/line,
+		// run the checks.
+		if ops, found := fullops[srcFileLine]; found {
 			for i := range ops {
 				if !ops[i].found && ops[i].opcode.FindString(asm) != "" {
 					ops[i].found = true
 				}
 			}
 		}
+	}
+	functionMarkers = append(functionMarkers, len(lines))
 
 	var failed []wantedAsmOpcode
 	for _, ops := range fullops {
@@ -1413,9 +1433,19 @@ func (t *test) asmCheck(outStr string, fn string, arch string, fullops map[strin
 		return failed[i].line < failed[j].line
 	})
 
+	lastFunction := -1
 	var errbuf bytes.Buffer
 	fmt.Fprintln(&errbuf)
 	for _, o := range failed {
+		// Dump the function in which this opcode check was supposed to
+		// pass but failed.
+		funcIdx := lineFuncMap[o.fileline]
+		if funcIdx != 0 && funcIdx != lastFunction {
+			funcLines := lines[functionMarkers[funcIdx]:functionMarkers[funcIdx+1]]
+			log.Println(strings.Join(funcLines, "\n"))
+			lastFunction = funcIdx // avoid printing same function twice
+		}
+
 		if o.negative {
 			fmt.Fprintf(&errbuf, "%s:%d: %s: wrong opcode found: %q\n", t.goFileName(), o.line, arch, o.opcode.String())
 		} else {