cmd/7g: reactivate componentgen

Update #10203

When the portable componentgen was introduced in b9602632 it
produced broken code on arm64 and was deactivated. In the month since
it looks like the underlying issues have been fixed so componentgen
produces working binaries that are slightly smaller, ~3kb reduction in
size for godoc binary.

Benchmarks are underwhelming, but where visible, trending towards
an improvement (this is with Minux's peep optimiser CL).

benchmark                          old ns/op       new ns/op       delta
BenchmarkBinaryTree17              15336842000     15002766000     -2.18%
BenchmarkFannkuch11                10848984000     10896931000     +0.44%
BenchmarkFmtFprintfEmpty           203             188             -7.39%
BenchmarkFmtFprintfString          753             720             -4.38%
BenchmarkFmtFprintfInt             667             670             +0.45%
BenchmarkFmtFprintfIntInt          1103            1102            -0.09%
BenchmarkFmtFprintfPrefixedInt     981             969             -1.22%
BenchmarkFmtFprintfFloat           1396            1348            -3.44%
BenchmarkFmtManyArgs               4151            4102            -1.18%
BenchmarkGobDecode                 34202360        32933020        -3.71%
BenchmarkGobEncode                 27579180        27438820        -0.51%
BenchmarkGzip                      1296119000      1285096000      -0.85%
BenchmarkGunzip                    291099800       289727200       -0.47%
BenchmarkHTTPClientServer          169476          169803          +0.19%
BenchmarkJSONEncode                70313600        69973400        -0.48%
BenchmarkJSONDecode                227811800       232875200       +2.22%
BenchmarkMandelbrot200             12985600        12996430        +0.08%
BenchmarkGoParse                   14708930        14507320        -1.37%
BenchmarkRegexpMatchEasy0_32       464             460             -0.86%
BenchmarkRegexpMatchEasy0_1K       4516            4517            +0.02%
BenchmarkRegexpMatchEasy1_32       452             454             +0.44%
BenchmarkRegexpMatchEasy1_1K       4664            4669            +0.11%
BenchmarkRegexpMatchMedium_32      602             602             +0.00%
BenchmarkRegexpMatchMedium_1K      172939          172494          -0.26%
BenchmarkRegexpMatchHard_32        9733            9577            -1.60%
BenchmarkRegexpMatchHard_1K        301356          298143          -1.07%
BenchmarkRevcomp                   2754334000      2753874000      -0.02%
BenchmarkTemplate                  315664000       311810800       -1.22%
BenchmarkTimeParse                 1034            989             -4.35%
BenchmarkTimeFormat                1118            1137            +1.70%

benchmark                         old MB/s     new MB/s     speedup
BenchmarkGobDecode                22.44        23.31        1.04x
BenchmarkGobEncode                27.83        27.97        1.01x
BenchmarkGzip                     14.97        15.10        1.01x
BenchmarkGunzip                   66.66        66.98        1.00x
BenchmarkJSONEncode               27.60        27.73        1.00x
BenchmarkJSONDecode               8.52         8.33         0.98x
BenchmarkGoParse                  3.94         3.99         1.01x
BenchmarkRegexpMatchEasy0_32      68.92        69.47        1.01x
BenchmarkRegexpMatchEasy0_1K      226.71       226.65       1.00x
BenchmarkRegexpMatchEasy1_32      70.75        70.42        1.00x
BenchmarkRegexpMatchEasy1_1K      219.55       219.28       1.00x
BenchmarkRegexpMatchMedium_32     1.66         1.66         1.00x
BenchmarkRegexpMatchMedium_1K     5.92         5.94         1.00x
BenchmarkRegexpMatchHard_32       3.29         3.34         1.02x
BenchmarkRegexpMatchHard_1K       3.40         3.43         1.01x
BenchmarkRevcomp                  92.28        92.29        1.00x
BenchmarkTemplate                 6.15         6.22         1.01x

Change-Id: I0b7d95388d6920fcbd7fe305df0c7c630a407726
Reviewed-on: https://go-review.googlesource.com/8636Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/7g/ggen.go

@@ -400,9 +400,9 @@ func clearfat(nl *gc.Node) {
 	w := uint64(uint64(nl.Type.Width))
 
 	// Avoid taking the address for simple enough types.
-	//if gc.Componentgen(nil, nl) {
-	//	return
-	//}
+	if gc.Componentgen(nil, nl) {
+		return
+	}
 
 	c := uint64(w % 8) // bytes
 	q := uint64(w / 8) // dwords