cmd, runtime: remove PC_F & PC_B globals on Wasm

Following the previous CL, this removes more global variables on
Wasm.

PC_B is used mostly for intra-function jumps, and for a function
telling its callee where to start or resume. This usage can be
served by a parameter. The top level loop (wasm_pc_f_loop) uses
PC_B for resuming a function. This value is either set by gogo,
or loaded from the Go stack at function return. Instead of
loading PC_B at each function return, we could make gogo stores
PC_B at the same stack location, and let the top level loop do
the load. This way, we don't need to use global PC_B to
communicate with the top level loop, and we can replace global
PC_B with a parameter.

PC_F is similar. It is even more so in that the only reader is
the top level loop. Let the top level loop read it from the stack,
and we can get rid of PC_F entirely.

PC_F and PC_B are used less entensively as SP, so this CL has
smaller performance gain.

Running on Chrome 74.0.3729.108 on Linux/AMD64,

name                   old time/op    new time/op    delta
BinaryTree17              16.6s ± 0%     16.2s ± 1%   -2.59%  (p=0.016 n=4+5)
Fannkuch11                11.1s ± 1%     10.8s ± 0%   -2.65%  (p=0.008 n=5+5)
FmtFprintfEmpty           231ns ± 1%     217ns ± 0%   -6.06%  (p=0.008 n=5+5)
FmtFprintfString          407ns ± 3%     375ns ± 2%   -7.81%  (p=0.008 n=5+5)
FmtFprintfInt             466ns ± 2%     430ns ± 0%   -7.79%  (p=0.016 n=5+4)
FmtFprintfIntInt          719ns ± 2%     673ns ± 2%   -6.37%  (p=0.008 n=5+5)
FmtFprintfPrefixedInt     706ns ± 1%     676ns ± 3%   -4.31%  (p=0.008 n=5+5)
FmtFprintfFloat          1.01µs ± 1%    0.97µs ± 1%   -4.30%  (p=0.008 n=5+5)
FmtManyArgs              2.67µs ± 1%    2.51µs ± 1%   -5.95%  (p=0.008 n=5+5)
GobDecode                30.7ms ± 9%    31.3ms ±34%     ~     (p=0.222 n=5+5)
GobEncode                24.2ms ±23%    20.2ms ± 0%  -16.36%  (p=0.016 n=5+4)
Gzip                      852ms ± 0%     823ms ± 0%   -3.38%  (p=0.016 n=4+5)
Gunzip                    160ms ± 1%     151ms ± 1%   -5.37%  (p=0.008 n=5+5)
JSONEncode               35.7ms ± 1%    34.3ms ± 1%   -3.81%  (p=0.008 n=5+5)
JSONDecode                247ms ± 8%     254ms ± 7%     ~     (p=0.548 n=5+5)
Mandelbrot200            5.39ms ± 0%    5.41ms ± 0%   +0.42%  (p=0.008 n=5+5)
GoParse                  18.5ms ± 1%    18.3ms ± 2%     ~     (p=0.343 n=4+4)
RegexpMatchEasy0_32       424ns ± 2%     397ns ± 0%   -6.23%  (p=0.008 n=5+5)
RegexpMatchEasy0_1K      2.88µs ± 0%    2.86µs ± 1%     ~     (p=0.079 n=5+5)
RegexpMatchEasy1_32       395ns ± 2%     370ns ± 1%   -6.23%  (p=0.008 n=5+5)
RegexpMatchEasy1_1K      3.26µs ± 0%    3.19µs ± 1%   -2.06%  (p=0.008 n=5+5)
RegexpMatchMedium_32      564ns ± 1%     532ns ± 0%   -5.71%  (p=0.008 n=5+5)
RegexpMatchMedium_1K      146µs ± 2%     140µs ± 1%   -4.62%  (p=0.008 n=5+5)
RegexpMatchHard_32       8.47µs ± 1%    7.91µs ± 1%   -6.65%  (p=0.008 n=5+5)
RegexpMatchHard_1K        253µs ± 1%     236µs ± 2%   -6.66%  (p=0.008 n=5+5)
Revcomp                   1.78s ± 4%     1.76s ± 5%     ~     (p=1.000 n=5+5)
Template                  292ms ±29%     269ms ± 5%     ~     (p=0.690 n=5+5)
TimeParse                1.61µs ± 4%    1.54µs ± 1%   -4.42%  (p=0.008 n=5+5)
TimeFormat               1.66µs ± 3%    1.58µs ± 1%   -5.22%  (p=0.008 n=5+5)
[Geo mean]                232µs          221µs        -4.54%

name                   old speed      new speed      delta
GobDecode              25.0MB/s ± 8%  25.1MB/s ±27%     ~     (p=0.222 n=5+5)
GobEncode              32.8MB/s ±21%  38.0MB/s ± 0%  +15.84%  (p=0.016 n=5+4)
Gzip                   22.8MB/s ± 0%  23.6MB/s ± 0%   +3.49%  (p=0.016 n=4+5)
Gunzip                  121MB/s ± 1%   128MB/s ± 1%   +5.68%  (p=0.008 n=5+5)
JSONEncode             54.4MB/s ± 1%  56.5MB/s ± 1%   +3.97%  (p=0.008 n=5+5)
JSONDecode             7.88MB/s ± 8%  7.65MB/s ± 8%     ~     (p=0.548 n=5+5)
GoParse                3.07MB/s ± 8%  3.00MB/s ±22%     ~     (p=0.579 n=5+5)
RegexpMatchEasy0_32    75.6MB/s ± 2%  80.5MB/s ± 0%   +6.58%  (p=0.008 n=5+5)
RegexpMatchEasy0_1K     356MB/s ± 0%   358MB/s ± 1%     ~     (p=0.095 n=5+5)
RegexpMatchEasy1_32    81.1MB/s ± 2%  86.5MB/s ± 1%   +6.69%  (p=0.008 n=5+5)
RegexpMatchEasy1_1K     314MB/s ± 0%   320MB/s ± 0%   +2.10%  (p=0.008 n=5+5)
RegexpMatchMedium_32   1.77MB/s ± 1%  1.88MB/s ± 0%   +6.09%  (p=0.016 n=5+4)
RegexpMatchMedium_1K   6.99MB/s ± 2%  7.33MB/s ± 1%   +4.83%  (p=0.008 n=5+5)
RegexpMatchHard_32     3.78MB/s ± 1%  4.04MB/s ± 1%   +7.04%  (p=0.008 n=5+5)
RegexpMatchHard_1K     4.04MB/s ± 1%  4.33MB/s ± 2%   +7.17%  (p=0.008 n=5+5)
Revcomp                 143MB/s ± 4%   145MB/s ± 5%     ~     (p=1.000 n=5+5)
Template               6.77MB/s ±24%  7.22MB/s ± 5%     ~     (p=0.690 n=5+5)
[Geo mean]             24.4MB/s       25.4MB/s        +4.18%

Change-Id: Ib80716e62992aec28b2c4a96af280c278f83aa49
Reviewed-on: https://go-review.googlesource.com/c/go/+/173980
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Richard Musiol <neelance@gmail.com>

1 files changed, 30 insertions, 24 deletions

diff --git a/src/runtime/rt0_js_wasm.s b/src/runtime/rt0_js_wasm.s
index c4efd9637c..b22c46e2e9 100644
--- a/src/runtime/rt0_js_wasm.s
+++ b/src/runtime/rt0_js_wasm.s
@@ -31,14 +31,9 @@ TEXT wasm_export_run(SB),NOSPLIT,$0
 	I64ExtendI32U
 	I64Store $8
 
-	I32Const $runtime·rt0_go(SB)
-	I32Const $16
-	I32ShrU
-	Set PC_F
-
-	I32Const $0
-	Set PC_B
-
+	I32Const $0 // entry PC_B
+	Call runtime·rt0_go(SB)
+	Drop
 	Call wasm_pc_f_loop(SB)
 
 	Return
@@ -46,14 +41,9 @@ TEXT wasm_export_run(SB),NOSPLIT,$0
 // wasm_export_resume gets called from JavaScript. It resumes the execution of Go code until it needs to wait for
 // an event.
 TEXT wasm_export_resume(SB),NOSPLIT,$0
-	I32Const $runtime·handleEvent(SB)
-	I32Const $16
-	I32ShrU
-	Set PC_F
-
 	I32Const $0
-	Set PC_B
-
+	Call runtime·handleEvent(SB)
+	Drop
 	Call wasm_pc_f_loop(SB)
 
 	Return
@@ -63,15 +53,30 @@ TEXT wasm_pc_f_loop(SB),NOSPLIT,$0
 // The WebAssembly stack may unwind, e.g. when switching goroutines.
 // The Go stack on the linear memory is then used to jump to the correct functions
 // with this loop, without having to restore the full WebAssembly stack.
-loop:
-	Loop
-		Get PC_F
-		CallIndirect $0
-		Drop
-
-		Get PAUSE
-		I32Eqz
-		BrIf loop
+// It is expected to have a pending call before entering the loop, so check PAUSE first.
+	Get PAUSE
+	I32Eqz
+	If
+	loop:
+		Loop
+			// Get PC_B & PC_F from -8(SP)
+			Get SP
+			I32Const $8
+			I32Sub
+			I32Load16U $0 // PC_B
+
+			Get SP
+			I32Const $8
+			I32Sub
+			I32Load16U $2 // PC_F
+
+			CallIndirect $0
+			Drop
+
+			Get PAUSE
+			I32Eqz
+			BrIf loop
+		End
 	End
 
 	I32Const $0
@@ -91,6 +96,7 @@ TEXT runtime·pause(SB), NOSPLIT, $0-8
 	RETUNWIND
 
 TEXT runtime·exit(SB), NOSPLIT, $0-4
+	I32Const $0
 	Call runtime·wasmExit(SB)
 	Drop
 	I32Const $1