[dev.ssa] cmd/compile: short-circuit empty blocks
Empty blocks are introduced to remove critical edges.
After regalloc, we can remove any of the added blocks
that are still empty.
Change-Id: I0b40e95ac3a6cc1e632a479443479532b6c5ccd9
Reviewed-on: https://go-review.googlesource.com/18833
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index b57958a..9dd5859 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -4183,23 +4183,36 @@
case ssa.OpAMD64LoweredNilCheck:
// Optimization - if the subsequent block has a load or store
// at the same address, we don't need to issue this instruction.
+ mem := v.Args[1]
for _, w := range v.Block.Succs[0].Values {
+ if w.Op == ssa.OpPhi {
+ if w.Type.IsMemory() {
+ mem = w
+ }
+ continue
+ }
if len(w.Args) == 0 || !w.Args[len(w.Args)-1].Type.IsMemory() {
// w doesn't use a store - can't be a memory op.
continue
}
- if w.Args[len(w.Args)-1] != v.Args[1] {
+ if w.Args[len(w.Args)-1] != mem {
v.Fatalf("wrong store after nilcheck v=%s w=%s", v, w)
}
switch w.Op {
case ssa.OpAMD64MOVQload, ssa.OpAMD64MOVLload, ssa.OpAMD64MOVWload, ssa.OpAMD64MOVBload,
ssa.OpAMD64MOVQstore, ssa.OpAMD64MOVLstore, ssa.OpAMD64MOVWstore, ssa.OpAMD64MOVBstore:
if w.Args[0] == v.Args[0] && w.Aux == nil && w.AuxInt >= 0 && w.AuxInt < minZeroPage {
+ if Debug_checknil != 0 && int(v.Line) > 1 {
+ Warnl(int(v.Line), "removed nil check")
+ }
return
}
case ssa.OpAMD64MOVQstoreconst, ssa.OpAMD64MOVLstoreconst, ssa.OpAMD64MOVWstoreconst, ssa.OpAMD64MOVBstoreconst:
off := ssa.StoreConst(v.AuxInt).Off()
if w.Args[0] == v.Args[0] && w.Aux == nil && off >= 0 && off < minZeroPage {
+ if Debug_checknil != 0 && int(v.Line) > 1 {
+ Warnl(int(v.Line), "removed nil check")
+ }
return
}
}
diff --git a/src/cmd/compile/internal/ssa/TODO b/src/cmd/compile/internal/ssa/TODO
index 403f98c..2f7973c 100644
--- a/src/cmd/compile/internal/ssa/TODO
+++ b/src/cmd/compile/internal/ssa/TODO
@@ -42,7 +42,6 @@
(all instructions, really)
- combine LEAQs
- store followed by load to same address
-- short circuit blocks which are just a jump (undo critical edge processing when no instructions are put in it by regalloc)
- (CMPconst [0] (AND x y)) -> (TEST x y)
- more (LOAD (ADDQ )) -> LOADIDX
- CMPL/SETEQ/TESTB/JEQ -> CMPL/JEQ
diff --git a/src/cmd/compile/internal/ssa/check.go b/src/cmd/compile/internal/ssa/check.go
index ca3bbfe..b743710 100644
--- a/src/cmd/compile/internal/ssa/check.go
+++ b/src/cmd/compile/internal/ssa/check.go
@@ -18,10 +18,12 @@
f.Fatalf("%s.Func=%s, want %s", b, b.Func.Name, f.Name)
}
- for i, c := range b.Succs {
- for j, d := range b.Succs {
- if i != j && c == d {
- f.Fatalf("%s.Succs has duplicate block %s", b, c)
+ if f.RegAlloc == nil {
+ for i, c := range b.Succs {
+ for j, d := range b.Succs {
+ if i != j && c == d {
+ f.Fatalf("%s.Succs has duplicate block %s", b, c)
+ }
}
}
}
@@ -34,6 +36,7 @@
// all successors are distinct. They will need to be distinct
// anyway for register allocation (duplicate successors implies
// the existence of critical edges).
+ // After regalloc we can allow non-distinct predecessors.
for _, p := range b.Preds {
var found bool
diff --git a/src/cmd/compile/internal/ssa/compile.go b/src/cmd/compile/internal/ssa/compile.go
index 64c1412..7a515f8 100644
--- a/src/cmd/compile/internal/ssa/compile.go
+++ b/src/cmd/compile/internal/ssa/compile.go
@@ -105,7 +105,8 @@
{"layout", layout}, // schedule blocks
{"schedule", schedule}, // schedule values
{"flagalloc", flagalloc}, // allocate flags register
- {"regalloc", regalloc},
+ {"regalloc", regalloc}, // allocate int & float registers
+ {"trim", trim}, // remove empty blocks
}
// Double-check phase ordering constraints.
@@ -148,6 +149,8 @@
{"schedule", "flagalloc"},
// regalloc needs flags to be allocated first.
{"flagalloc", "regalloc"},
+ // trim needs regalloc to be done first.
+ {"regalloc", "trim"},
}
func init() {
diff --git a/src/cmd/compile/internal/ssa/trim.go b/src/cmd/compile/internal/ssa/trim.go
new file mode 100644
index 0000000..594d2aa
--- /dev/null
+++ b/src/cmd/compile/internal/ssa/trim.go
@@ -0,0 +1,37 @@
+// Copyright 2016 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.
+
+package ssa
+
+// trim removes blocks with no code in them.
+// These blocks were inserted to remove critical edges.
+func trim(f *Func) {
+ i := 0
+ for _, b := range f.Blocks {
+ if b.Kind != BlockPlain || len(b.Values) != 0 || len(b.Preds) != 1 {
+ f.Blocks[i] = b
+ i++
+ continue
+ }
+ // TODO: handle len(b.Preds)>1 case.
+
+ // Splice b out of the graph.
+ pred := b.Preds[0]
+ succ := b.Succs[0]
+ for j, s := range pred.Succs {
+ if s == b {
+ pred.Succs[j] = succ
+ }
+ }
+ for j, p := range succ.Preds {
+ if p == b {
+ succ.Preds[j] = pred
+ }
+ }
+ }
+ for j := i; j < len(f.Blocks); j++ {
+ f.Blocks[j] = nil
+ }
+ f.Blocks = f.Blocks[:i]
+}
