cmd/5g, cmd/6g, cmd/8g: remove width check for componentgen.

The move to 64-bit ints in 6g made componentgen ineffective.
In componentgen, the code already selects which values it can handle.

On amd64:
benchmark                 old ns/op    new ns/op    delta
BenchmarkBinaryTree17    9477970000   9582314000   +1.10%
BenchmarkFannkuch11      5928750000   5255080000  -11.36%
BenchmarkGobDecode         37103040     31451120  -15.23%
BenchmarkGobEncode         16042490     16844730   +5.00%
BenchmarkGzip             811337400    741373600   -8.62%
BenchmarkGunzip           197928700    192844500   -2.57%
BenchmarkJSONEncode       224164100    140064200  -37.52%
BenchmarkJSONDecode       258346800    231829000  -10.26%
BenchmarkMandelbrot200      7561780      7601615   +0.53%
BenchmarkParse             12970340     11624360  -10.38%
BenchmarkRevcomp         1969917000   1699137000  -13.75%
BenchmarkTemplate         296182000    263117400  -11.16%

R=nigeltao, dave, daniel.morsing
CC=golang-dev
https://golang.org/cl/6821052

src/cmd/5g/cgen.c

@@ -1356,9 +1356,9 @@ sgen(Node *n, Node *res, int64 w)
 		return;
 	}
 
-	if(w == 8 || w == 12)
-		if(componentgen(n, res))
-			return;
+	// Avoid taking the address for simple enough types.
+	if(componentgen(n, res))
+		return;
 	
 	// determine alignment.
 	// want to avoid unaligned access, so have to use
@@ -1495,9 +1495,10 @@ cadable(Node *n)
 }
 
 /*
- * copy a structure component by component
+ * copy a composite value by moving its individual components.
+ * Slices, strings and interfaces are supported.
+ * nr is N when assigning a zero value.
  * return 1 if can do, 0 if cant.
- * nr is N for copy zero
  */
 int
 componentgen(Node *nr, Node *nl)

src/cmd/5g/ggen.c

@@ -618,9 +618,9 @@ clearfat(Node *nl)
 
 
 	w = nl->type->width;
-	if(w == 8 || w == 12)
-		if(componentgen(N, nl))
-			return;
+	// Avoid taking the address for simple enough types.
+	if(componentgen(N, nl))
+		return;
 
 	c = w % 4;	// bytes
 	q = w / 4;	// quads

src/cmd/6g/cgen.c

@@ -1254,9 +1254,9 @@ sgen(Node *n, Node *ns, int64 w)
 	if(w < 0)
 		fatal("sgen copy %lld", w);
 
-	if(w == 16)
-		if(componentgen(n, ns))
-			return;
+	// Avoid taking the address for simple enough types.
+	if(componentgen(n, ns))
+		return;
 	
 	if(w == 0) {
 		// evaluate side effects only
@@ -1378,9 +1378,10 @@ cadable(Node *n)
 }
 
 /*
- * copy a structure component by component
+ * copy a composite value by moving its individual components.
+ * Slices, strings and interfaces are supported.
+ * nr is N when assigning a zero value.
  * return 1 if can do, 0 if cant.
- * nr is N for copy zero
  */
 int
 componentgen(Node *nr, Node *nl)

src/cmd/6g/ggen.c

@@ -1028,9 +1028,9 @@ clearfat(Node *nl)
 
 
 	w = nl->type->width;
-	if(w == 16)
-		if(componentgen(N, nl))
-			return;
+	// Avoid taking the address for simple enough types.
+	if(componentgen(N, nl))
+		return;
 
 	c = w % 8;	// bytes
 	q = w / 8;	// quads

src/cmd/8g/cgen.c

@@ -1276,10 +1276,9 @@ sgen(Node *n, Node *res, int64 w)
 		return;
 	}
 
-	if (w == 8 || w == 12) {
-		if(componentgen(n, res))
-			return;
-	}
+	// Avoid taking the address for simple enough types.
+	if(componentgen(n, res))
+		return;
 
 	// offset on the stack
 	osrc = stkof(n);
@@ -1381,9 +1380,10 @@ cadable(Node *n)
 }
 
 /*
- * copy a structure component by component
+ * copy a composite value by moving its individual components.
+ * Slices, strings and interfaces are supported.
+ * nr is N when assigning a zero value.
  * return 1 if can do, 0 if cant.
- * nr is N for copy zero
  */
 int
 componentgen(Node *nr, Node *nl)

src/cmd/8g/ggen.c

@@ -59,9 +59,9 @@ clearfat(Node *nl)
 		dump("\nclearfat", nl);
 
 	w = nl->type->width;
-	if(w == 8 || w == 12)
-		if(componentgen(N, nl))
-			return;
+	// Avoid taking the address for simple enough types.
+	if(componentgen(N, nl))
+		return;
 
 	c = w % 4;	// bytes
 	q = w / 4;	// quads