cmd/gc: correct handling of globals, func args, results

Globals, function arguments, and results are special cases in
registerization.

Globals must be flushed aggressively, because nearly any
operation can cause a panic, and the recovery code must see
the latest values. Globals also must be loaded aggressively,
because nearly any store through a pointer might be updating a
global: the compiler cannot see all the "address of"
operations on globals, especially exported globals. To
accomplish this, mark all globals as having their address
taken, which effectively disables registerization.

If a function contains a defer statement, the function results
must be flushed aggressively, because nearly any operation can
cause a panic, and the deferred code may call recover, causing
the original function to return the current values of its
function results. To accomplish this, mark all function
results as having their address taken if the function contains
any defer statements. This causes not just aggressive flushing
but also aggressive loading. The aggressive loading is
overkill but the best we can do in the current code.

Function arguments must be considered live at all safe points
in a function, because garbage collection always preserves
them: they must be up-to-date in order to be preserved
correctly. Accomplish this by marking them live at all call
sites. An earlier attempt at this marked function arguments as
having their address taken, which disabled registerization
completely, making programs slower. This CL's solution allows
registerization while preserving safety. The benchmark speedup
is caused by being able to registerize again (the earlier CL
lost the same amount).

benchmark                old ns/op     new ns/op     delta
BenchmarkEqualPort32     61.4          56.0          -8.79%

benchmark                old MB/s     new MB/s     speedup
BenchmarkEqualPort32     521.56       570.97       1.09x

Fixes issue 1304. (again)
Fixes issue 7944. (again)
Fixes issue 7984.
Fixes issue 7995.

LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, iant, r
https://codereview.appspot.com/97500044

1 files changed, 51 insertions, 51 deletions

diff --git a/test/nilptr3.go b/test/nilptr3.go
index 08597a02d..2757daef0 100644
--- a/test/nilptr3.go
+++ b/test/nilptr3.go
@@ -17,7 +17,7 @@ type Struct struct {
 type BigStruct struct {
 	X int
 	Y float64
-	A [1<<20]int
+	A [1 << 20]int
 	Z string
 }
 
@@ -29,93 +29,94 @@ type Empty1 struct {
 }
 
 var (
-	intp *int
-	arrayp *[10]int
-	array0p *[0]int
-	bigarrayp *[1<<26]int
-	structp *Struct
+	intp       *int
+	arrayp     *[10]int
+	array0p    *[0]int
+	bigarrayp  *[1 << 26]int
+	structp    *Struct
 	bigstructp *BigStruct
-	emptyp *Empty
-	empty1p *Empty1
+	emptyp     *Empty
+	empty1p    *Empty1
 )
 
 func f1() {
 	_ = *intp // ERROR "generated nil check"
-	
+
 	// This one should be removed but the block copy needs
 	// to be turned into its own pseudo-op in order to see
 	// the indirect.
 	_ = *arrayp // ERROR "generated nil check"
-	
-	// 0-byte indirect doesn't suffice
+
+	// 0-byte indirect doesn't suffice.
+	// we don't registerize globals, so there are no removed repeated nil checks.
+	_ = *array0p // ERROR "generated nil check"
 	_ = *array0p // ERROR "generated nil check"
-	_ = *array0p // ERROR "removed repeated nil check" 386
 
-	_ = *intp // ERROR "removed repeated nil check"
-	_ = *arrayp // ERROR "removed repeated nil check"
+	_ = *intp    // ERROR "generated nil check"
+	_ = *arrayp  // ERROR "generated nil check"
 	_ = *structp // ERROR "generated nil check"
-	_ = *emptyp // ERROR "generated nil check"
-	_ = *arrayp // ERROR "removed repeated nil check"
+	_ = *emptyp  // ERROR "generated nil check"
+	_ = *arrayp  // ERROR "generated nil check"
 }
 
 func f2() {
 	var (
-		intp *int
-		arrayp *[10]int
-		array0p *[0]int
-		bigarrayp *[1<<20]int
-		structp *Struct
+		intp       *int
+		arrayp     *[10]int
+		array0p    *[0]int
+		bigarrayp  *[1 << 20]int
+		structp    *Struct
 		bigstructp *BigStruct
-		emptyp *Empty
-		empty1p *Empty1
+		emptyp     *Empty
+		empty1p    *Empty1
 	)
 
-	_ = *intp // ERROR "generated nil check"
-	_ = *arrayp // ERROR "generated nil check"
-	_ = *array0p // ERROR "generated nil check"
-	_ = *array0p // ERROR "removed repeated nil check"
-	_ = *intp // ERROR "removed repeated nil check"
-	_ = *arrayp // ERROR "removed repeated nil check"
-	_ = *structp // ERROR "generated nil check"
-	_ = *emptyp // ERROR "generated nil check"
-	_ = *arrayp // ERROR "removed repeated nil check"
-	_ = *bigarrayp // ERROR "generated nil check" ARM removed nil check before indirect!!
+	_ = *intp       // ERROR "generated nil check"
+	_ = *arrayp     // ERROR "generated nil check"
+	_ = *array0p    // ERROR "generated nil check"
+	_ = *array0p    // ERROR "removed repeated nil check"
+	_ = *intp       // ERROR "removed repeated nil check"
+	_ = *arrayp     // ERROR "removed repeated nil check"
+	_ = *structp    // ERROR "generated nil check"
+	_ = *emptyp     // ERROR "generated nil check"
+	_ = *arrayp     // ERROR "removed repeated nil check"
+	_ = *bigarrayp  // ERROR "generated nil check" ARM removed nil check before indirect!!
 	_ = *bigstructp // ERROR "generated nil check"
-	_ = *empty1p // ERROR "generated nil check"
+	_ = *empty1p    // ERROR "generated nil check"
 }
 
 func fx10k() *[10000]int
-var b bool
 
+var b bool
 
 func f3(x *[10000]int) {
 	// Using a huge type and huge offsets so the compiler
 	// does not expect the memory hardware to fault.
 	_ = x[9999] // ERROR "generated nil check"
-	
+
 	for {
 		if x[9999] != 0 { // ERROR "generated nil check"
 			break
 		}
 	}
-	
-	x = fx10k() 
+
+	x = fx10k()
 	_ = x[9999] // ERROR "generated nil check"
 	if b {
 		_ = x[9999] // ERROR "removed repeated nil check"
 	} else {
 		_ = x[9999] // ERROR "removed repeated nil check"
-	}	
+	}
 	_ = x[9999] // ERROR "generated nil check"
 
-	x = fx10k() 
+	x = fx10k()
 	if b {
 		_ = x[9999] // ERROR "generated nil check"
 	} else {
 		_ = x[9999] // ERROR "generated nil check"
-	}	
+	}
 	_ = x[9999] // ERROR "generated nil check"
-	
+
 	fx10k()
 	// This one is a bit redundant, if we figured out that
 	// x wasn't going to change across the function call.
@@ -145,7 +146,7 @@ func f3b() {
 	_ = &x[9] // ERROR "removed repeated nil check"
 }
 
-func fx10() *[10]int 
+func fx10() *[10]int
 
 func f4(x *[10]int) {
 	// Most of these have no checks because a real memory reference follows,
@@ -153,14 +154,14 @@ func f4(x *[10]int) {
 	// in the first unmapped page of memory.
 
 	_ = x[9] // ERROR "removed nil check before indirect"
-	
+
 	for {
 		if x[9] != 0 { // ERROR "removed nil check before indirect"
 			break
 		}
 	}
-	
-	x = fx10() 
+
+	x = fx10()
 	_ = x[9] // ERROR "removed nil check before indirect"
 	if b {
 		_ = x[9] // ERROR "removed nil check before indirect"
@@ -169,17 +170,17 @@ func f4(x *[10]int) {
 	}
 	_ = x[9] // ERROR "removed nil check before indirect"
 
-	x = fx10() 
+	x = fx10()
 	if b {
 		_ = x[9] // ERROR "removed nil check before indirect"
 	} else {
 		_ = &x[9] // ERROR "generated nil check"
-	}	
+	}
 	_ = x[9] // ERROR "removed nil check before indirect"
-	
+
 	fx10()
 	_ = x[9] // ERROR "removed nil check before indirect"
-	
+
 	x = fx10()
 	y := fx10()
 	_ = &x[9] // ERROR "generated nil check"
@@ -188,4 +189,3 @@ func f4(x *[10]int) {
 	x = y
 	_ = &x[9] // ERROR "removed repeated nil check"
 }
-