cmd/compile: restore missing columns in ssa.html

If the final pass(es) are identical during ssa.html generation,
they are persisted in-memory as "pendingPhases" but never get
written as a column in the html. This change flushes those
in-memory phases.

Fixes #38242

Change-Id: Id13477dcbe7b419a818bb457861b2422ba5ef4bc
Reviewed-on: https://go-review.googlesource.com/c/go/+/227182
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

2 files changed, 23 insertions, 4 deletions

diff --git a/src/cmd/compile/internal/ssa/compile.go b/src/cmd/compile/internal/ssa/compile.go
index 3da3b8985f..2dbe9cf405 100644
--- a/src/cmd/compile/internal/ssa/compile.go
+++ b/src/cmd/compile/internal/ssa/compile.go
@@ -136,6 +136,11 @@ func Compile(f *Func) {
 		}
 	}
 
+	if f.HTMLWriter != nil {
+		// Ensure we write any pending phases to the html
+		f.HTMLWriter.flushPhases()
+	}
+
 	if f.ruleMatches != nil {
 		var keys []string
 		for key := range f.ruleMatches {
diff --git a/src/cmd/compile/internal/ssa/html.go b/src/cmd/compile/internal/ssa/html.go
index 1b083917dc..f39106f450 100644
--- a/src/cmd/compile/internal/ssa/html.go
+++ b/src/cmd/compile/internal/ssa/html.go
@@ -774,14 +774,28 @@ func (w *HTMLWriter) WritePhase(phase, title string) {
 	w.pendingPhases = append(w.pendingPhases, phase)
 	w.pendingTitles = append(w.pendingTitles, title)
 	if !bytes.Equal(hash, w.prevHash) {
-		phases := strings.Join(w.pendingPhases, "  +  ")
-		w.WriteMultiTitleColumn(phases, w.pendingTitles, fmt.Sprintf("hash-%x", hash), w.Func.HTML(phase, w.dot))
-		w.pendingPhases = w.pendingPhases[:0]
-		w.pendingTitles = w.pendingTitles[:0]
+		w.flushPhases()
 	}
 	w.prevHash = hash
 }
 
+// flushPhases collects any pending phases and titles, writes them to the html, and resets the pending slices.
+func (w *HTMLWriter) flushPhases() {
+	phaseLen := len(w.pendingPhases)
+	if phaseLen == 0 {
+		return
+	}
+	phases := strings.Join(w.pendingPhases, "  +  ")
+	w.WriteMultiTitleColumn(
+		phases,
+		w.pendingTitles,
+		fmt.Sprintf("hash-%x", w.prevHash),
+		w.Func.HTML(w.pendingPhases[phaseLen-1], w.dot),
+	)
+	w.pendingPhases = w.pendingPhases[:0]
+	w.pendingTitles = w.pendingTitles[:0]
+}
+
 // FuncLines contains source code for a function to be displayed
 // in sources column.
 type FuncLines struct {