Add new gas metering method: mutable global + local gas function (#34)

* fix misprints in doc comments

* added global gas tracker variable and local gas fn

* all exported functions of the module to accept a new param and to set the gas_left global to its value at their very start

* make module support both gas metering methods

* tests fixed for the old metering method

* better naming

* MutableGlobal metering method implemented, tests for the old method pass

* gas_metering::tests updated and pass

* all tests udpdated and pass

* emacs backup files to .gitignore

* docs updated

* clippy fix

* iff = if and only if

* more clippy

* docs misprints fixes

* refactored to have Backend trait and two implementations in separate sub-modules

* docs updated

* fixed old benches (updating them is coming next)

* added bench for an instrumented wasm-coremark

* updated benches: added them for both gas_metering instrumentations

* benches contest first ver

* added debug prints to the bench

* refactored to better fit frontend-backend pattern

* docs update

* updated benches

* design updated on feedback

* re-structured sub-modules

re-structured sub-modules & updated docs

* docs improved

* addressed latest feedback comments

* re-writed the local gas function

* coremark benches show ~20% performance improvement

* fix ci: test + clippy

* save before re-factoring prepare_in_wasm()

* bare_call_16 shows 16% worse perf

* + fibonacci recursive bench

* refactored benchmarks

* + factorial recursive bench

* benches on wasmi fixtures show no perf improvement, coremark runs ~20% faster being instrumented with mutable_global gas metering

* charge gas for local gas func isntructions execution

* replaced benchmark which requires multi_value feature

* save: optimized gas func a bit (benches work, fixture tests fail)

* 1033% overhead on many_blocks.wasm when mut_global gas_metering together with stack_height

* size overhead test for both gas metering methods + stack limiter

* added more benches

* improved print_size_overhead test

* test for comparing size overheads of two gas_metering injectors

* before optimization: benches + size overhead

* optimization try-1: inline part of gas func instructions: +benches +size overheads

* optimization try-2: inline hot path of gas fn:  +benches +size overheads

* opt try-3: count for gas fn cost on the caller side: +benches +size overhead

* revert to initial version but with static gas fn cost on the caller side: +benches +sizes

* tests fixed

* use newest wasmi 0.20: +benches +docs updated

* use if-else block instead of Return: +benches

* fix tests

* clippy fix

* addressed review comments

* Update changelog

Co-authored-by: Alexander Theißen <alex.theissen@me.com>

tests/expectations/gas/branch_mut_global.wat

@@ -0,0 +1,47 @@
+(module
+  (type (;0;) (func (result i32)))
+  (type (;1;) (func (param i64)))
+  (func $fibonacci_with_break (;0;) (type 0) (result i32)
+    (local $x i32) (local $y i32)
+    i64.const 24
+    call 1
+    block ;; label = @1
+      i32.const 0
+      local.set $x
+      i32.const 1
+      local.set $y
+      local.get $x
+      local.get $y
+      local.tee $x
+      i32.add
+      local.set $y
+      i32.const 1
+      br_if 0 (;@1;)
+      i64.const 16
+      call 1
+      local.get $x
+      local.get $y
+      local.tee $x
+      i32.add
+      local.set $y
+    end
+    local.get $y
+  )
+  (func (;1;) (type 1) (param i64)
+    global.get 0
+    local.get 0
+    i64.ge_u
+    if ;; label = @1
+      global.get 0
+      local.get 0
+      i64.sub
+      global.set 0
+    else
+      i64.const -1
+      global.set 0
+      unreachable
+    end
+  )
+  (global (;0;) (mut i64) i64.const 0)
+  (export "gas_left" (global 0))
+)

tests/expectations/gas/call_mut_global.wat

@@ -0,0 +1,38 @@
+(module
+  (type (;0;) (func (param i32 i32) (result i32)))
+  (type (;1;) (func (param i64)))
+  (func $add_locals (;0;) (type 0) (param $x i32) (param $y i32) (result i32)
+    (local $t i32)
+    i64.const 16
+    call 2
+    local.get $x
+    local.get $y
+    call $add
+    local.set $t
+    local.get $t
+  )
+  (func $add (;1;) (type 0) (param $x i32) (param $y i32) (result i32)
+    i64.const 14
+    call 2
+    local.get $x
+    local.get $y
+    i32.add
+  )
+  (func (;2;) (type 1) (param i64)
+    global.get 0
+    local.get 0
+    i64.ge_u
+    if ;; label = @1
+      global.get 0
+      local.get 0
+      i64.sub
+      global.set 0
+    else
+      i64.const -1
+      global.set 0
+      unreachable
+    end
+  )
+  (global (;0;) (mut i64) i64.const 0)
+  (export "gas_left" (global 0))
+)

tests/expectations/gas/ifs_mut_global.wat

@@ -0,0 +1,38 @@
+(module
+  (type (;0;) (func (param i32) (result i32)))
+  (type (;1;) (func (param i64)))
+  (func (;0;) (type 0) (param $x i32) (result i32)
+    i64.const 13
+    call 1
+    i32.const 1
+    if (result i32) ;; label = @1
+      i64.const 14
+      call 1
+      local.get $x
+      i32.const 1
+      i32.add
+    else
+      i64.const 13
+      call 1
+      local.get $x
+      i32.popcnt
+    end
+  )
+  (func (;1;) (type 1) (param i64)
+    global.get 0
+    local.get 0
+    i64.ge_u
+    if ;; label = @1
+      global.get 0
+      local.get 0
+      i64.sub
+      global.set 0
+    else
+      i64.const -1
+      global.set 0
+      unreachable
+    end
+  )
+  (global (;0;) (mut i64) i64.const 0)
+  (export "gas_left" (global 0))
+)

tests/expectations/gas/simple_mut_global.wat

@@ -0,0 +1,43 @@
+(module
+  (type (;0;) (func))
+  (type (;1;) (func (param i64)))
+  (func (;0;) (type 0)
+    i64.const 13
+    call 2
+    i32.const 1
+    if ;; label = @1
+      i64.const 12
+      call 2
+      loop ;; label = @2
+        i64.const 13
+        call 2
+        i32.const 123
+        drop
+      end
+    end
+  )
+  (func (;1;) (type 0)
+    i64.const 12
+    call 2
+    block ;; label = @1
+    end
+  )
+  (func (;2;) (type 1) (param i64)
+    global.get 0
+    local.get 0
+    i64.ge_u
+    if ;; label = @1
+      global.get 0
+      local.get 0
+      i64.sub
+      global.set 0
+    else
+      i64.const -1
+      global.set 0
+      unreachable
+    end
+  )
+  (global (;0;) (mut i64) i64.const 0)
+  (export "simple" (func 0))
+  (export "gas_left" (global 0))
+)

tests/expectations/gas/start_mut_global.wat

@@ -0,0 +1,36 @@
+(module
+  (type (;0;) (func (param i32 i32)))
+  (type (;1;) (func))
+  (type (;2;) (func (param i64)))
+  (import "env" "ext_return" (func $ext_return (;0;) (type 0)))
+  (import "env" "memory" (memory (;0;) 1 1))
+  (func $start (;1;) (type 1)
+    i64.const 15
+    call 3
+    i32.const 8
+    i32.const 4
+    call $ext_return
+    unreachable
+  )
+  (func (;2;) (type 1))
+  (func (;3;) (type 2) (param i64)
+    global.get 0
+    local.get 0
+    i64.ge_u
+    if ;; label = @1
+      global.get 0
+      local.get 0
+      i64.sub
+      global.set 0
+    else
+      i64.const -1
+      global.set 0
+      unreachable
+    end
+  )
+  (global (;0;) (mut i64) i64.const 0)
+  (export "call" (func 2))
+  (export "gas_left" (global 0))
+  (start $start)
+  (data (;0;) (i32.const 8) "\01\02\03\04")
+)