cmd/compile: reduce rulegen's for loop verbosity

A lot of the naked for loops begin like:

	for {
		v := b.Control
		if v.Op != OpConstBool {
			break
		}
		...
		return true
	}

Instead, write them out in a more compact and readable way:

	for v.Op == OpConstBool {
		...
		return true
	}

This requires the addition of two bytes.Buffer writers, as this helps us
make a decision based on future pieces of generated code. This probably
makes rulegen slightly slower, but that's not noticeable; the code
generation still takes ~3.5s on my laptop, excluding build time.

The "v := b.Control" declaration can be moved to the top of each
function. Even though the rules can modify b.Control when firing, they
also make the function return, so v can't be used again.

While at it, remove three unnecessary lines from the top of each
rewriteBlock func.

In total, this results in ~4k lines removed from the generated code, and
a slight improvement in readability.

Change-Id: I317e4c6a4842c64df506f4513375475fad2aeec5
Reviewed-on: https://go-review.googlesource.com/c/go/+/167399
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 34 insertions, 165 deletions

diff --git a/src/cmd/compile/internal/ssa/rewriteMIPS64.go b/src/cmd/compile/internal/ssa/rewriteMIPS64.go
index d9efa99261..453b81e75f 100644
--- a/src/cmd/compile/internal/ssa/rewriteMIPS64.go
+++ b/src/cmd/compile/internal/ssa/rewriteMIPS64.go
@@ -10036,21 +10036,16 @@ func rewriteValueMIPS64_OpZeroExt8to64_0(v *Value) bool {
 }
 func rewriteBlockMIPS64(b *Block) bool {
 	config := b.Func.Config
-	_ = config
-	fe := b.Func.fe
-	_ = fe
 	typ := &config.Types
 	_ = typ
+	v := b.Control
+	_ = v
 	switch b.Kind {
 	case BlockMIPS64EQ:
 		// match: (EQ (FPFlagTrue cmp) yes no)
 		// cond:
 		// result: (FPF cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64FPFlagTrue {
-				break
-			}
+		for v.Op == OpMIPS64FPFlagTrue {
 			cmp := v.Args[0]
 			b.Kind = BlockMIPS64FPF
 			b.SetControl(cmp)
@@ -10060,11 +10055,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (EQ (FPFlagFalse cmp) yes no)
 		// cond:
 		// result: (FPT cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64FPFlagFalse {
-				break
-			}
+		for v.Op == OpMIPS64FPFlagFalse {
 			cmp := v.Args[0]
 			b.Kind = BlockMIPS64FPT
 			b.SetControl(cmp)
@@ -10074,11 +10065,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (EQ (XORconst [1] cmp:(SGT _ _)) yes no)
 		// cond:
 		// result: (NE cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64XORconst {
-				break
-			}
+		for v.Op == OpMIPS64XORconst {
 			if v.AuxInt != 1 {
 				break
 			}
@@ -10095,11 +10082,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (EQ (XORconst [1] cmp:(SGTU _ _)) yes no)
 		// cond:
 		// result: (NE cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64XORconst {
-				break
-			}
+		for v.Op == OpMIPS64XORconst {
 			if v.AuxInt != 1 {
 				break
 			}
@@ -10116,11 +10099,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (EQ (XORconst [1] cmp:(SGTconst _)) yes no)
 		// cond:
 		// result: (NE cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64XORconst {
-				break
-			}
+		for v.Op == OpMIPS64XORconst {
 			if v.AuxInt != 1 {
 				break
 			}
@@ -10136,11 +10115,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (EQ (XORconst [1] cmp:(SGTUconst _)) yes no)
 		// cond:
 		// result: (NE cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64XORconst {
-				break
-			}
+		for v.Op == OpMIPS64XORconst {
 			if v.AuxInt != 1 {
 				break
 			}
@@ -10156,11 +10131,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (EQ (SGTUconst [1] x) yes no)
 		// cond:
 		// result: (NE x yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64SGTUconst {
-				break
-			}
+		for v.Op == OpMIPS64SGTUconst {
 			if v.AuxInt != 1 {
 				break
 			}
@@ -10173,11 +10144,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (EQ (SGTU x (MOVVconst [0])) yes no)
 		// cond:
 		// result: (EQ x yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64SGTU {
-				break
-			}
+		for v.Op == OpMIPS64SGTU {
 			_ = v.Args[1]
 			x := v.Args[0]
 			v_1 := v.Args[1]
@@ -10195,11 +10162,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (EQ (SGTconst [0] x) yes no)
 		// cond:
 		// result: (GEZ x yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64SGTconst {
-				break
-			}
+		for v.Op == OpMIPS64SGTconst {
 			if v.AuxInt != 0 {
 				break
 			}
@@ -10212,11 +10175,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (EQ (SGT x (MOVVconst [0])) yes no)
 		// cond:
 		// result: (LEZ x yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64SGT {
-				break
-			}
+		for v.Op == OpMIPS64SGT {
 			_ = v.Args[1]
 			x := v.Args[0]
 			v_1 := v.Args[1]
@@ -10234,11 +10193,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (EQ (MOVVconst [0]) yes no)
 		// cond:
 		// result: (First nil yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			if v.AuxInt != 0 {
 				break
 			}
@@ -10250,11 +10205,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (EQ (MOVVconst [c]) yes no)
 		// cond: c != 0
 		// result: (First nil no yes)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			c := v.AuxInt
 			if !(c != 0) {
 				break
@@ -10269,11 +10220,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (GEZ (MOVVconst [c]) yes no)
 		// cond: c >= 0
 		// result: (First nil yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			c := v.AuxInt
 			if !(c >= 0) {
 				break
@@ -10286,11 +10233,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (GEZ (MOVVconst [c]) yes no)
 		// cond: c < 0
 		// result: (First nil no yes)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			c := v.AuxInt
 			if !(c < 0) {
 				break
@@ -10305,11 +10248,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (GTZ (MOVVconst [c]) yes no)
 		// cond: c > 0
 		// result: (First nil yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			c := v.AuxInt
 			if !(c > 0) {
 				break
@@ -10322,11 +10261,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (GTZ (MOVVconst [c]) yes no)
 		// cond: c <= 0
 		// result: (First nil no yes)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			c := v.AuxInt
 			if !(c <= 0) {
 				break
@@ -10342,8 +10277,6 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// cond:
 		// result: (NE cond yes no)
 		for {
-			v := b.Control
-			_ = v
 			cond := b.Control
 			b.Kind = BlockMIPS64NE
 			b.SetControl(cond)
@@ -10354,11 +10287,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (LEZ (MOVVconst [c]) yes no)
 		// cond: c <= 0
 		// result: (First nil yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			c := v.AuxInt
 			if !(c <= 0) {
 				break
@@ -10371,11 +10300,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (LEZ (MOVVconst [c]) yes no)
 		// cond: c > 0
 		// result: (First nil no yes)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			c := v.AuxInt
 			if !(c > 0) {
 				break
@@ -10390,11 +10315,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (LTZ (MOVVconst [c]) yes no)
 		// cond: c < 0
 		// result: (First nil yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			c := v.AuxInt
 			if !(c < 0) {
 				break
@@ -10407,11 +10328,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (LTZ (MOVVconst [c]) yes no)
 		// cond: c >= 0
 		// result: (First nil no yes)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			c := v.AuxInt
 			if !(c >= 0) {
 				break
@@ -10426,11 +10343,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (FPFlagTrue cmp) yes no)
 		// cond:
 		// result: (FPT cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64FPFlagTrue {
-				break
-			}
+		for v.Op == OpMIPS64FPFlagTrue {
 			cmp := v.Args[0]
 			b.Kind = BlockMIPS64FPT
 			b.SetControl(cmp)
@@ -10440,11 +10353,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (FPFlagFalse cmp) yes no)
 		// cond:
 		// result: (FPF cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64FPFlagFalse {
-				break
-			}
+		for v.Op == OpMIPS64FPFlagFalse {
 			cmp := v.Args[0]
 			b.Kind = BlockMIPS64FPF
 			b.SetControl(cmp)
@@ -10454,11 +10363,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (XORconst [1] cmp:(SGT _ _)) yes no)
 		// cond:
 		// result: (EQ cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64XORconst {
-				break
-			}
+		for v.Op == OpMIPS64XORconst {
 			if v.AuxInt != 1 {
 				break
 			}
@@ -10475,11 +10380,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (XORconst [1] cmp:(SGTU _ _)) yes no)
 		// cond:
 		// result: (EQ cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64XORconst {
-				break
-			}
+		for v.Op == OpMIPS64XORconst {
 			if v.AuxInt != 1 {
 				break
 			}
@@ -10496,11 +10397,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (XORconst [1] cmp:(SGTconst _)) yes no)
 		// cond:
 		// result: (EQ cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64XORconst {
-				break
-			}
+		for v.Op == OpMIPS64XORconst {
 			if v.AuxInt != 1 {
 				break
 			}
@@ -10516,11 +10413,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (XORconst [1] cmp:(SGTUconst _)) yes no)
 		// cond:
 		// result: (EQ cmp yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64XORconst {
-				break
-			}
+		for v.Op == OpMIPS64XORconst {
 			if v.AuxInt != 1 {
 				break
 			}
@@ -10536,11 +10429,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (SGTUconst [1] x) yes no)
 		// cond:
 		// result: (EQ x yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64SGTUconst {
-				break
-			}
+		for v.Op == OpMIPS64SGTUconst {
 			if v.AuxInt != 1 {
 				break
 			}
@@ -10553,11 +10442,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (SGTU x (MOVVconst [0])) yes no)
 		// cond:
 		// result: (NE x yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64SGTU {
-				break
-			}
+		for v.Op == OpMIPS64SGTU {
 			_ = v.Args[1]
 			x := v.Args[0]
 			v_1 := v.Args[1]
@@ -10575,11 +10460,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (SGTconst [0] x) yes no)
 		// cond:
 		// result: (LTZ x yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64SGTconst {
-				break
-			}
+		for v.Op == OpMIPS64SGTconst {
 			if v.AuxInt != 0 {
 				break
 			}
@@ -10592,11 +10473,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (SGT x (MOVVconst [0])) yes no)
 		// cond:
 		// result: (GTZ x yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64SGT {
-				break
-			}
+		for v.Op == OpMIPS64SGT {
 			_ = v.Args[1]
 			x := v.Args[0]
 			v_1 := v.Args[1]
@@ -10614,11 +10491,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (MOVVconst [0]) yes no)
 		// cond:
 		// result: (First nil no yes)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			if v.AuxInt != 0 {
 				break
 			}
@@ -10631,11 +10504,7 @@ func rewriteBlockMIPS64(b *Block) bool {
 		// match: (NE (MOVVconst [c]) yes no)
 		// cond: c != 0
 		// result: (First nil yes no)
-		for {
-			v := b.Control
-			if v.Op != OpMIPS64MOVVconst {
-				break
-			}
+		for v.Op == OpMIPS64MOVVconst {
 			c := v.AuxInt
 			if !(c != 0) {
 				break