[dev.ssa] cmd/compile/internal/ssa: reuse symbols
Reuse the ArgSymbol for nodes so that the Aux values will be equal for cse.
Change-Id: Iaae80bd19ff2d3f51b6c9049fd860e04baa6f175
Reviewed-on: https://go-review.googlesource.com/15930
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Todd Neal <todd@tneal.org>
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 312d494..7219ffd 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -87,17 +87,19 @@
s.startBlock(s.f.Entry)
s.vars[&memVar] = s.startmem
+ s.varsyms = map[*Node]interface{}{}
+
// Generate addresses of local declarations
s.decladdrs = map[*Node]*ssa.Value{}
for d := fn.Func.Dcl; d != nil; d = d.Next {
n := d.N
switch n.Class {
case PPARAM:
- aux := &ssa.ArgSymbol{Typ: n.Type, Node: n}
+ aux := s.lookupSymbol(n, &ssa.ArgSymbol{Typ: n.Type, Node: n})
s.decladdrs[n] = s.entryNewValue1A(ssa.OpAddr, Ptrto(n.Type), aux, s.sp)
case PAUTO | PHEAP:
// TODO this looks wrong for PAUTO|PHEAP, no vardef, but also no definition
- aux := &ssa.AutoSymbol{Typ: n.Type, Node: n}
+ aux := s.lookupSymbol(n, &ssa.AutoSymbol{Typ: n.Type, Node: n})
s.decladdrs[n] = s.entryNewValue1A(ssa.OpAddr, Ptrto(n.Type), aux, s.sp)
case PPARAM | PHEAP, PPARAMOUT | PHEAP:
// This ends up wrong, have to do it at the PARAM node instead.
@@ -234,6 +236,9 @@
// addresses of PPARAM and PPARAMOUT variables.
decladdrs map[*Node]*ssa.Value
+ // symbols for PEXTERN, PAUTO and PPARAMOUT variables so they can be reused.
+ varsyms map[*Node]interface{}
+
// starting values. Memory, frame pointer, and stack pointer
startmem *ssa.Value
sp *ssa.Value
@@ -1247,7 +1252,7 @@
s.stmtList(n.Ninit)
switch n.Op {
case OCFUNC:
- aux := &ssa.ExternSymbol{n.Type, n.Left.Sym}
+ aux := s.lookupSymbol(n, &ssa.ExternSymbol{n.Type, n.Left.Sym})
return s.entryNewValue1A(ssa.OpAddr, n.Type, aux, s.sb)
case OPARAM:
addr := s.addr(n, false)
@@ -2187,6 +2192,25 @@
return 0
}
+// lookupSymbol is used to retrieve the symbol (Extern, Arg or Auto) used for a particular node.
+// This improves the effectiveness of cse by using the same Aux values for the
+// same symbols.
+func (s *state) lookupSymbol(n *Node, sym interface{}) interface{} {
+ switch sym.(type) {
+ default:
+ s.Fatalf("sym %v is of uknown type %T", sym, sym)
+ case *ssa.ExternSymbol, *ssa.ArgSymbol, *ssa.AutoSymbol:
+ // these are the only valid types
+ }
+
+ if lsym, ok := s.varsyms[n]; ok {
+ return lsym
+ } else {
+ s.varsyms[n] = sym
+ return sym
+ }
+}
+
// addr converts the address of the expression n to SSA, adds it to s and returns the SSA result.
// The value that the returned Value represents is guaranteed to be non-nil.
// If bounded is true then this address does not require a nil check for its operand
@@ -2226,7 +2250,9 @@
aux := &ssa.AutoSymbol{Typ: n.Type, Node: n}
return s.newValue1A(ssa.OpAddr, Ptrto(n.Type), aux, s.sp)
case PPARAMOUT: // Same as PAUTO -- cannot generate LEA early.
- aux := &ssa.ArgSymbol{Typ: n.Type, Node: n}
+ // ensure that we reuse symbols for out parameters so
+ // that cse works on their addresses
+ aux := s.lookupSymbol(n, &ssa.ArgSymbol{Typ: n.Type, Node: n})
return s.newValue1A(ssa.OpAddr, Ptrto(n.Type), aux, s.sp)
case PAUTO | PHEAP, PPARAM | PHEAP, PPARAMOUT | PHEAP, PPARAMREF:
return s.expr(n.Name.Heapaddr)
