all: remove unnecessary allocations from w.WriteString(fmt.Sprint*(...)) by fmt.Fprint*(w, ...)

Noticed in a manual audit from a customer codebase that the pattern

    w.WriteString(fmt.Sprint*(args...))

was less efficient and in most cases we can just invoke:

    fmt.Fprint*(w, args...)

and from the simple benchmarks we can see quick wins in all dimensions:

$ benchstat before.txt after.txt
name            old time/op    new time/op    delta
DetailString-8    5.48µs ±23%    4.40µs ±11%  -19.79%  (p=0.000 n=20+17)

name            old alloc/op   new alloc/op   delta
DetailString-8    2.63kB ± 0%    2.11kB ± 0%  -19.76%  (p=0.000 n=20+20)

name            old allocs/op  new allocs/op  delta
DetailString-8      63.0 ± 0%      50.0 ± 0%  -20.63%  (p=0.000 n=20+20)

Change-Id: I47a2827cd34d6b92644900b1bd5f4c0a3287bdb1
Reviewed-on: https://go-review.googlesource.com/c/go/+/429861
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: hopehook <hopehook@golangcn.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

4 files changed, 7 insertions, 7 deletions

diff --git a/src/cmd/compile/internal/abt/avlint32.go b/src/cmd/compile/internal/abt/avlint32.go
index eed5fa5d38..e0998f5bac 100644
--- a/src/cmd/compile/internal/abt/avlint32.go
+++ b/src/cmd/compile/internal/abt/avlint32.go
@@ -339,7 +339,7 @@ func (t *T) String() string {
 		}
 		b.WriteString(strconv.FormatInt(int64(k), 10))
 		b.WriteString(":")
-		b.WriteString(fmt.Sprint(v))
+		fmt.Fprint(&b, v)
 	}
 	return b.String()
 }
diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index 21b8fbc8ec..88d43b9915 100644
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -7271,7 +7271,7 @@ func genssa(f *ssa.Func, pp *objw.Progs) {
 			}
 			buf.WriteString("</dt>")
 			buf.WriteString("<dd class=\"ssa-prog\">")
-			buf.WriteString(fmt.Sprintf("%.5d <span class=\"l%v line-number\">(%s)</span> %s", p.Pc, p.InnermostLineNumber(), p.InnermostLineNumberHTML(), html.EscapeString(p.InstructionString())))
+			fmt.Fprintf(&buf, "%.5d <span class=\"l%v line-number\">(%s)</span> %s", p.Pc, p.InnermostLineNumber(), p.InnermostLineNumberHTML(), html.EscapeString(p.InstructionString()))
 			buf.WriteString("</dd>")
 		}
 		buf.WriteString("</dl>")
diff --git a/src/cmd/compile/internal/syntax/scanner_test.go b/src/cmd/compile/internal/syntax/scanner_test.go
index 2deb3bbf84..450ec1ff8a 100644
--- a/src/cmd/compile/internal/syntax/scanner_test.go
+++ b/src/cmd/compile/internal/syntax/scanner_test.go
@@ -88,10 +88,10 @@ func TestEmbeddedTokens(t *testing.T) {
 	// make source
 	var buf bytes.Buffer
 	for i, s := range sampleTokens {
-		buf.WriteString("\t\t\t\t"[:i&3])                            // leading indentation
-		buf.WriteString(s.src)                                       // token
-		buf.WriteString("        "[:i&7])                            // trailing spaces
-		buf.WriteString(fmt.Sprintf("/*line foo:%d */ // bar\n", i)) // comments + newline (don't crash w/o directive handler)
+		buf.WriteString("\t\t\t\t"[:i&3])                 // leading indentation
+		buf.WriteString(s.src)                            // token
+		buf.WriteString("        "[:i&7])                 // trailing spaces
+		fmt.Fprintf(&buf, "/*line foo:%d */ // bar\n", i) // comments + newline (don't crash w/o directive handler)
 	}
 
 	// scan source
diff --git a/src/cmd/compile/internal/types/fmt.go b/src/cmd/compile/internal/types/fmt.go
index c6e99d26c2..990f2e5f52 100644
--- a/src/cmd/compile/internal/types/fmt.go
+++ b/src/cmd/compile/internal/types/fmt.go
@@ -577,7 +577,7 @@ func tconv2(b *bytes.Buffer, t *Type, verb rune, mode fmtMode, visited map[*Type
 		} else {
 			b.WriteString("tp")
 			// Print out the pointer value for now to disambiguate type params
-			b.WriteString(fmt.Sprintf("%p", t))
+			fmt.Fprintf(b, "%p", t)
 		}
 
 	case TUNION: