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cmd/compile: minor comment improvements/corrections

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Change-Id: Ie0934f1528d58d4971cdef726d3e2d23cf3935d3
Reviewed-on: https://go-review.googlesource.com/87475
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Alexandru Moșoi <alexandru@mosoi.ro>
This commit is contained in:
Austin Clements 2018-01-09 14:40:54 -05:00
parent b55eedd173
commit 491f409a32
2 changed files with 10 additions and 3 deletions
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2
src/cmd/compile/internal/ssa/func.go
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@ -28,7 +28,7 @@ type Func struct {
Cache *Cache // re-usable cache Cache *Cache // re-usable cache
fe Frontend // frontend state associated with this Func, callbacks into compiler frontend fe Frontend // frontend state associated with this Func, callbacks into compiler frontend
pass *pass // current pass information (name, options, etc.) pass *pass // current pass information (name, options, etc.)
Name string // e.g. bytes·Compare Name string // e.g. NewFunc or (*Func).NumBlocks (no package prefix)
Type *types.Type // type signature of the function. Type *types.Type // type signature of the function.
Blocks []*Block // unordered set of all basic blocks (note: not indexable by ID) Blocks []*Block // unordered set of all basic blocks (note: not indexable by ID)
Entry *Block // the entry basic block Entry *Block // the entry basic block

11
src/cmd/compile/internal/ssa/prove.go
View file

@ -90,6 +90,12 @@ type limitFact struct {
} }
// factsTable keeps track of relations between pairs of values. // factsTable keeps track of relations between pairs of values.
//
// The fact table logic is sound, but incomplete. Outside of a few
// special cases, it performs no deduction or arithmetic. While there
// are known decision procedures for this, the ad hoc approach taken
// by the facts table is effective for real code while remaining very
// efficient.
type factsTable struct { type factsTable struct {
facts map[pair]relation // current known set of relation facts map[pair]relation // current known set of relation
stack []fact // previous sets of relations stack []fact // previous sets of relations
@ -433,8 +439,8 @@ var (
// TODO: OpIsInBounds actually test 0 <= a < b. This means // TODO: OpIsInBounds actually test 0 <= a < b. This means
// that the positive branch learns signed/LT and unsigned/LT // that the positive branch learns signed/LT and unsigned/LT
// but the negative branch only learns unsigned/GE. // but the negative branch only learns unsigned/GE.
OpIsInBounds: {unsigned, lt}, OpIsInBounds: {unsigned, lt}, // 0 <= arg0 < arg1
OpIsSliceInBounds: {unsigned, lt | eq}, OpIsSliceInBounds: {unsigned, lt | eq}, // 0 <= arg0 <= arg1
} }
) )
@ -625,6 +631,7 @@ func updateRestrictions(parent *Block, ft *factsTable, t domain, v, w *Value, r
// simplifyBlock simplifies block known the restrictions in ft. // simplifyBlock simplifies block known the restrictions in ft.
// Returns which branch must always be taken. // Returns which branch must always be taken.
func simplifyBlock(ft *factsTable, b *Block) branch { func simplifyBlock(ft *factsTable, b *Block) branch {
// Replace OpSlicemask operations in b with constants where possible.
for _, v := range b.Values { for _, v := range b.Values {
if v.Op != OpSlicemask { if v.Op != OpSlicemask {
continue continue