cmd/compile: Repurpose old sliceopt.go for prove phase.

Adapt old test for prove's bounds check elimination.
Added missing rule to generic rules that lead to differences
between 32 and 64 bit platforms on sliceopt test.
Added debugging to prove.go that was helpful-to-necessary to
discover that missing rule.
Lowered debugging level on prove.go from 3 to 1; no idea
why it was previously 3.

Change-Id: I09de206aeb2fced9f2796efe2bfd4a59927eda0c
Reviewed-on: https://go-review.googlesource.com/23290
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/gc/ssa.go

@@ -670,9 +670,18 @@ func (s *state) stmt(n *Node) {
 				// If the slice can be SSA'd, it'll be on the stack,
 				// so there will be no write barriers,
 				// so there's no need to attempt to prevent them.
-				if samesafeexpr(n.Left, rhs.List.First()) && !s.canSSA(n.Left) {
-					s.append(rhs, true)
-					return
+				if samesafeexpr(n.Left, rhs.List.First()) {
+					if !s.canSSA(n.Left) {
+						if Debug_append > 0 {
+							Warnl(n.Lineno, "append: len-only update")
+						}
+						s.append(rhs, true)
+						return
+					} else {
+						if Debug_append > 0 { // replicating old diagnostic message
+							Warnl(n.Lineno, "append: len-only update (in local slice)")
+						}
+					}
 				}
 			}
 		}

src/cmd/compile/internal/ssa/gen/generic.rules

@@ -749,6 +749,8 @@
 // a more comprehensive set.
 (SliceLen (SliceMake _ (Const64 <t> [c]) _)) -> (Const64 <t> [c])
 (SliceCap (SliceMake _ _ (Const64 <t> [c]))) -> (Const64 <t> [c])
+(SliceLen (SliceMake _ (Const32 <t> [c]) _)) -> (Const32 <t> [c])
+(SliceCap (SliceMake _ _ (Const32 <t> [c]))) -> (Const32 <t> [c])
 (SlicePtr (SliceMake (SlicePtr x) _ _)) -> (SlicePtr x)
 (SliceLen (SliceMake _ (SliceLen x) _)) -> (SliceLen x)
 (SliceCap (SliceMake _ _ (SliceCap x))) -> (SliceCap x)

src/cmd/compile/internal/ssa/prove.go

@@ -4,7 +4,10 @@
 
 package ssa
 
-import "math"
+import (
+	"fmt"
+	"math"
+)
 
 type branch int
 
@@ -74,6 +77,10 @@ type limit struct {
 	umin, umax uint64 // umin <= value <= umax, unsigned
 }
 
+func (l limit) String() string {
+	return fmt.Sprintf("sm,SM,um,UM=%d,%d,%d,%d", l.min, l.max, l.umin, l.umax)
+}
+
 var noLimit = limit{math.MinInt64, math.MaxInt64, 0, math.MaxUint64}
 
 // a limitFact is a limit known for a particular value.
@@ -191,7 +198,7 @@ func (ft *factsTable) get(v, w *Value, d domain) relation {
 
 // update updates the set of relations between v and w in domain d
 // restricting it to r.
-func (ft *factsTable) update(v, w *Value, d domain, r relation) {
+func (ft *factsTable) update(parent *Block, v, w *Value, d domain, r relation) {
 	if lessByID(w, v) {
 		v, w = w, v
 		r = reverseBits[r]
@@ -293,6 +300,9 @@ func (ft *factsTable) update(v, w *Value, d domain, r relation) {
 		}
 		ft.limitStack = append(ft.limitStack, limitFact{v.ID, old})
 		ft.limits[v.ID] = lim
+		if v.Block.Func.pass.debug > 2 {
+			v.Block.Func.Config.Warnl(parent.Line, "parent=%s, new limits %s %s %s", parent, v, w, lim.String())
+		}
 	}
 }
 
@@ -478,11 +488,11 @@ func prove(f *Func) {
 			if branch != unknown {
 				ft.checkpoint()
 				c := parent.Control
-				updateRestrictions(ft, boolean, nil, c, lt|gt, branch)
+				updateRestrictions(parent, ft, boolean, nil, c, lt|gt, branch)
 				if tr, has := domainRelationTable[parent.Control.Op]; has {
 					// When we branched from parent we learned a new set of
 					// restrictions. Update the factsTable accordingly.
-					updateRestrictions(ft, tr.d, c.Args[0], c.Args[1], tr.r, branch)
+					updateRestrictions(parent, ft, tr.d, c.Args[0], c.Args[1], tr.r, branch)
 				}
 			}
 
@@ -538,7 +548,7 @@ func getBranch(sdom SparseTree, p *Block, b *Block) branch {
 
 // updateRestrictions updates restrictions from the immediate
 // dominating block (p) using r. r is adjusted according to the branch taken.
-func updateRestrictions(ft *factsTable, t domain, v, w *Value, r relation, branch branch) {
+func updateRestrictions(parent *Block, ft *factsTable, t domain, v, w *Value, r relation, branch branch) {
 	if t == 0 || branch == unknown {
 		// Trivial case: nothing to do, or branch unknown.
 		// Shoult not happen, but just in case.
@@ -550,7 +560,7 @@ func updateRestrictions(ft *factsTable, t domain, v, w *Value, r relation, branc
 	}
 	for i := domain(1); i <= t; i <<= 1 {
 		if t&i != 0 {
-			ft.update(v, w, i, r)
+			ft.update(parent, v, w, i, r)
 		}
 	}
 }
@@ -566,13 +576,21 @@ func simplifyBlock(ft *factsTable, b *Block) branch {
 	m := ft.get(nil, b.Control, boolean)
 	if m == lt|gt {
 		if b.Func.pass.debug > 0 {
-			b.Func.Config.Warnl(b.Line, "Proved boolean %s", b.Control.Op)
+			if b.Func.pass.debug > 1 {
+				b.Func.Config.Warnl(b.Line, "Proved boolean %s (%s)", b.Control.Op, b.Control)
+			} else {
+				b.Func.Config.Warnl(b.Line, "Proved boolean %s", b.Control.Op)
+			}
 		}
 		return positive
 	}
 	if m == eq {
 		if b.Func.pass.debug > 0 {
-			b.Func.Config.Warnl(b.Line, "Disproved boolean %s", b.Control.Op)
+			if b.Func.pass.debug > 1 {
+				b.Func.Config.Warnl(b.Line, "Disproved boolean %s (%s)", b.Control.Op, b.Control)
+			} else {
+				b.Func.Config.Warnl(b.Line, "Disproved boolean %s", b.Control.Op)
+			}
 		}
 		return negative
 	}
@@ -599,13 +617,21 @@ func simplifyBlock(ft *factsTable, b *Block) branch {
 		m := ft.get(a0, a1, d)
 		if m != 0 && tr.r&m == m {
 			if b.Func.pass.debug > 0 {
-				b.Func.Config.Warnl(b.Line, "Proved %s", c.Op)
+				if b.Func.pass.debug > 1 {
+					b.Func.Config.Warnl(b.Line, "Proved %s (%s)", c.Op, c)
+				} else {
+					b.Func.Config.Warnl(b.Line, "Proved %s", c.Op)
+				}
 			}
 			return positive
 		}
 		if m != 0 && ((lt|eq|gt)^tr.r)&m == m {
 			if b.Func.pass.debug > 0 {
-				b.Func.Config.Warnl(b.Line, "Disproved %s", c.Op)
+				if b.Func.pass.debug > 1 {
+					b.Func.Config.Warnl(b.Line, "Disproved %s (%s)", c.Op, c)
+				} else {
+					b.Func.Config.Warnl(b.Line, "Disproved %s", c.Op)
+				}
 			}
 			return negative
 		}
@@ -620,7 +646,11 @@ func simplifyBlock(ft *factsTable, b *Block) branch {
 		m := ft.get(a0, a1, signed)
 		if m != 0 && tr.r&m == m {
 			if b.Func.pass.debug > 0 {
-				b.Func.Config.Warnl(b.Line, "Proved non-negative bounds %s", c.Op)
+				if b.Func.pass.debug > 1 {
+					b.Func.Config.Warnl(b.Line, "Proved non-negative bounds %s (%s)", c.Op, c)
+				} else {
+					b.Func.Config.Warnl(b.Line, "Proved non-negative bounds %s", c.Op)
+				}
 			}
 			return positive
 		}
@@ -635,6 +665,9 @@ func isNonNegative(v *Value) bool {
 	case OpConst64:
 		return v.AuxInt >= 0
 
+	case OpConst32:
+		return int32(v.AuxInt) >= 0
+
 	case OpStringLen, OpSliceLen, OpSliceCap,
 		OpZeroExt8to64, OpZeroExt16to64, OpZeroExt32to64:
 		return true

src/cmd/compile/internal/ssa/rewritegeneric.go

@@ -9656,6 +9656,25 @@ func rewriteValuegeneric_OpSliceCap(v *Value, config *Config) bool {
 		v.AuxInt = c
 		return true
 	}
+	// match: (SliceCap (SliceMake _ _ (Const32 <t> [c])))
+	// cond:
+	// result: (Const32 <t> [c])
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpSliceMake {
+			break
+		}
+		v_0_2 := v_0.Args[2]
+		if v_0_2.Op != OpConst32 {
+			break
+		}
+		t := v_0_2.Type
+		c := v_0_2.AuxInt
+		v.reset(OpConst32)
+		v.Type = t
+		v.AuxInt = c
+		return true
+	}
 	// match: (SliceCap (SliceMake _ _ (SliceCap x)))
 	// cond:
 	// result: (SliceCap x)
@@ -9714,6 +9733,25 @@ func rewriteValuegeneric_OpSliceLen(v *Value, config *Config) bool {
 		v.AuxInt = c
 		return true
 	}
+	// match: (SliceLen (SliceMake _ (Const32 <t> [c]) _))
+	// cond:
+	// result: (Const32 <t> [c])
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpSliceMake {
+			break
+		}
+		v_0_1 := v_0.Args[1]
+		if v_0_1.Op != OpConst32 {
+			break
+		}
+		t := v_0_1.Type
+		c := v_0_1.AuxInt
+		v.reset(OpConst32)
+		v.Type = t
+		v.AuxInt = c
+		return true
+	}
 	// match: (SliceLen (SliceMake _ (SliceLen x) _))
 	// cond:
 	// result: (SliceLen x)

test/prove.go

@@ -1,5 +1,5 @@
 // +build amd64
-// errorcheck -0 -d=ssa/prove/debug=3
+// errorcheck -0 -d=ssa/prove/debug=1
 
 // Copyright 2016 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style

test/sliceopt.go

@@ -0,0 +1,70 @@
+// errorcheck -0 -d=append,slice,ssa/prove/debug=1
+
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Check optimization results for append and slicing.
+
+package main
+
+func a1(x []int, y int) []int {
+	x = append(x, y) // ERROR "append: len-only update \(in local slice\)$"
+	return x
+}
+
+func a2(x []int, y int) []int {
+	return append(x, y)
+}
+
+func a3(x *[]int, y int) {
+	*x = append(*x, y) // ERROR "append: len-only update$"
+}
+
+// s1_if_false_then_anything
+func s1_if_false_then_anything(x **[]int, xs **string, i, j int) {
+	z := (**x)[0:i]
+	z = z[i : i+1]
+	println(z) // if we get here, then we have proven that i==i+1 (this cannot happen, but the program is still being analyzed...)
+
+	zs := (**xs)[0:i] // since i=i+1 is proven, i+1 is "in bounds", ha-ha
+	zs = zs[i : i+1]  // ERROR "Proved boolean IsSliceInBounds$"
+	println(zs)
+}
+
+func s1(x **[]int, xs **string, i, j int) {
+	var z []int
+	z = (**x)[2:]
+	z = (**x)[2:len(**x)] // ERROR "Proved boolean IsSliceInBounds$"
+	z = (**x)[2:cap(**x)] // ERROR "Proved IsSliceInBounds$"
+	z = (**x)[i:i]        // -ERROR "Proved IsSliceInBounds"
+	z = (**x)[1:i:i]      // ERROR "Proved boolean IsSliceInBounds$"
+	z = (**x)[i:j:0]
+	z = (**x)[i:0:j] // ERROR "Disproved IsSliceInBounds$"
+	z = (**x)[0:i:j] // ERROR "Proved boolean IsSliceInBounds$"
+	z = (**x)[0:]    // ERROR "slice: omit slice operation$"
+	z = (**x)[2:8]   // ERROR "Disproved Eq(32|64)$"
+	z = (**x)[2:2]   // ERROR "Disproved Eq(32|64)$" "Proved boolean IsSliceInBounds$"
+	z = (**x)[0:i]   // ERROR "Proved boolean IsSliceInBounds$"
+	z = (**x)[2:i:8] // ERROR "Disproved IsSliceInBounds$" "Proved IsSliceInBounds$" "Proved boolean IsSliceInBounds$"
+	z = (**x)[i:2:i] // ERROR "Proved IsSliceInBounds$" "Proved boolean IsSliceInBounds$"
+
+	z = z[0:i] // ERROR "Proved boolean IsSliceInBounds"
+	z = z[0:i : i+1]
+	z = z[i : i+1] // ERROR "Proved boolean IsSliceInBounds$"
+
+	println(z)
+
+	var zs string
+	zs = (**xs)[2:]
+	zs = (**xs)[2:len(**xs)] // ERROR "Proved IsSliceInBounds$" "Proved boolean IsSliceInBounds$"
+	zs = (**xs)[i:i]         // -ERROR "Proved boolean IsSliceInBounds"
+	zs = (**xs)[0:]          // ERROR "slice: omit slice operation$"
+	zs = (**xs)[2:8]
+	zs = (**xs)[2:2] // ERROR "Proved boolean IsSliceInBounds$"
+	zs = (**xs)[0:i] // ERROR "Proved boolean IsSliceInBounds$"
+
+	zs = zs[0:i]     // See s1_if_false_then_anything above to explain the counterfactual bounds check result below
+	zs = zs[i : i+1] // ERROR "Proved boolean IsSliceInBounds$"
+	println(zs)
+}