cmd/compile: keep value use counts in SSA
Keep track of how many uses each Value has. Each appearance in
Value.Args and in Block.Control counts once.
The number of uses of a value is generically useful to
constrain rewrite rules. For instance, we might want to
prevent merging index operations into loads if the same
index expression is used lots of times.
But I have one use in particular for which the use count is required.
We must make sure we don't combine ops with loads if the load has
more than one use. Otherwise, we may split a single load
into multiple loads and that breaks perceived behavior in
the presence of races. In particular, the load of m.state
in sync/mutex.go:Lock can't be done twice. (I have a separate
CL which triggers the mutex failure. This CL has a test which
demonstrates a similar failure.)
Change-Id: Icaafa479239f48632a069d0c3f624e6ebc6b1f0e
Reviewed-on: https://go-review.googlesource.com/20790
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Todd Neal <todd@tneal.org>
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 6bf5899..716be35 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -540,7 +540,7 @@
m := s.mem()
b := s.endBlock()
b.Kind = ssa.BlockExit
- b.Control = m
+ b.SetControl(m)
// TODO: never rewrite OPANIC to OCALLFUNC in the
// first place. Need to wait until all backends
// go through SSA.
@@ -920,7 +920,7 @@
m := s.mem()
b := s.endBlock()
b.Kind = ssa.BlockRet
- b.Control = m
+ b.SetControl(m)
return b
}
@@ -1795,7 +1795,7 @@
b := s.endBlock()
b.Kind = ssa.BlockIf
- b.Control = el
+ b.SetControl(el)
// In theory, we should set b.Likely here based on context.
// However, gc only gives us likeliness hints
// in a single place, for plain OIF statements,
@@ -2039,7 +2039,7 @@
b := s.endBlock()
b.Kind = ssa.BlockIf
b.Likely = ssa.BranchUnlikely
- b.Control = cmp
+ b.SetControl(cmp)
b.AddEdgeTo(grow)
b.AddEdgeTo(assign)
@@ -2143,7 +2143,7 @@
c := s.expr(cond)
b := s.endBlock()
b.Kind = ssa.BlockIf
- b.Control = c
+ b.SetControl(c)
b.Likely = ssa.BranchPrediction(likely) // gc and ssa both use -1/0/+1 for likeliness
b.AddEdgeTo(yes)
b.AddEdgeTo(no)
@@ -2396,7 +2396,7 @@
s.vars[&memVar] = call
b := s.endBlock()
b.Kind = ssa.BlockCall
- b.Control = call
+ b.SetControl(call)
b.AddEdgeTo(bNext)
if k == callDefer {
// Add recover edge to exit code.
@@ -2654,7 +2654,7 @@
chk := s.newValue2(ssa.OpNilCheck, ssa.TypeVoid, ptr, s.mem())
b := s.endBlock()
b.Kind = ssa.BlockCheck
- b.Control = chk
+ b.SetControl(chk)
bNext := s.f.NewBlock(ssa.BlockPlain)
b.AddEdgeTo(bNext)
s.startBlock(bNext)
@@ -2692,7 +2692,7 @@
func (s *state) check(cmp *ssa.Value, fn *Node) {
b := s.endBlock()
b.Kind = ssa.BlockIf
- b.Control = cmp
+ b.SetControl(cmp)
b.Likely = ssa.BranchLikely
bNext := s.f.NewBlock(ssa.BlockPlain)
line := s.peekLine()
@@ -2740,7 +2740,7 @@
b := s.endBlock()
if !returns {
b.Kind = ssa.BlockExit
- b.Control = call
+ b.SetControl(call)
call.AuxInt = off
if len(results) > 0 {
Fatalf("panic call can't have results")
@@ -2748,7 +2748,7 @@
return nil
}
b.Kind = ssa.BlockCall
- b.Control = call
+ b.SetControl(call)
bNext := s.f.NewBlock(ssa.BlockPlain)
b.AddEdgeTo(bNext)
s.startBlock(bNext)
@@ -2793,7 +2793,7 @@
b := s.endBlock()
b.Kind = ssa.BlockIf
b.Likely = ssa.BranchUnlikely
- b.Control = flag
+ b.SetControl(flag)
b.AddEdgeTo(bThen)
b.AddEdgeTo(bElse)
@@ -2838,7 +2838,7 @@
b := s.endBlock()
b.Kind = ssa.BlockIf
b.Likely = ssa.BranchUnlikely
- b.Control = flag
+ b.SetControl(flag)
b.AddEdgeTo(bThen)
b.AddEdgeTo(bElse)
@@ -3049,7 +3049,7 @@
b := s.endBlock()
b.Kind = ssa.BlockIf
b.Likely = ssa.BranchLikely
- b.Control = cmp
+ b.SetControl(cmp)
// Generate code for non-zero length slice case.
nz := s.f.NewBlock(ssa.BlockPlain)
@@ -3150,7 +3150,7 @@
cmp := s.newValue2(cvttab.geq, Types[TBOOL], x, s.zeroVal(ft))
b := s.endBlock()
b.Kind = ssa.BlockIf
- b.Control = cmp
+ b.SetControl(cmp)
b.Likely = ssa.BranchLikely
bThen := s.f.NewBlock(ssa.BlockPlain)
@@ -3198,7 +3198,7 @@
cmp := s.newValue2(ssa.OpEqPtr, Types[TBOOL], x, nilValue)
b := s.endBlock()
b.Kind = ssa.BlockIf
- b.Control = cmp
+ b.SetControl(cmp)
b.Likely = ssa.BranchUnlikely
bThen := s.f.NewBlock(ssa.BlockPlain)
@@ -3269,7 +3269,7 @@
cmp := s.newValue2(cvttab.ltf, Types[TBOOL], x, twoToThe63)
b := s.endBlock()
b.Kind = ssa.BlockIf
- b.Control = cmp
+ b.SetControl(cmp)
b.Likely = ssa.BranchLikely
bThen := s.f.NewBlock(ssa.BlockPlain)
@@ -3318,7 +3318,7 @@
isnonnil := s.newValue2(ssa.OpNeqPtr, Types[TBOOL], tab, s.constNil(byteptr))
b := s.endBlock()
b.Kind = ssa.BlockIf
- b.Control = isnonnil
+ b.SetControl(isnonnil)
b.Likely = ssa.BranchLikely
bLoad := s.f.NewBlock(ssa.BlockPlain)
@@ -3360,7 +3360,7 @@
cond := s.newValue2(ssa.OpEqPtr, Types[TBOOL], typ, target)
b := s.endBlock()
b.Kind = ssa.BlockIf
- b.Control = cond
+ b.SetControl(cond)
b.Likely = ssa.BranchLikely
byteptr := Ptrto(Types[TUINT8])
