cmd/compile: try to rewrite loops to count down

[gostls13.git] / src / cmd / compile / internal / ssa / loopbce.go

diff --git a/src/cmd/compile/internal/ssa/loopbce.go b/src/cmd/compile/internal/ssa/loopbce.go
index b7dfaa33e3bf46523e57d52b98474dc30d719837..3dbd7350ae9da37fe92319bb8ed3e671b83cb161 100644 (file)
--- a/src/cmd/compile/internal/ssa/loopbce.go
+++ b/src/cmd/compile/internal/ssa/loopbce.go
@@ -13,12 +13,14 @@ import (
 type indVarFlags uint8
 
 const (
-       indVarMinExc indVarFlags = 1 << iota // minimum value is exclusive (default: inclusive)
-       indVarMaxInc                         // maximum value is inclusive (default: exclusive)
+       indVarMinExc    indVarFlags = 1 << iota // minimum value is exclusive (default: inclusive)
+       indVarMaxInc                            // maximum value is inclusive (default: exclusive)
+       indVarCountDown                         // if set the iteration starts at max and count towards min (default: min towards max)
 )
 
 type indVar struct {
        ind   *Value // induction variable
+       nxt   *Value // the incremented variable
        min   *Value // minimum value, inclusive/exclusive depends on flags
        max   *Value // maximum value, inclusive/exclusive depends on flags
        entry *Block // entry block in the loop.
@@ -277,6 +279,7 @@ func findIndVar(f *Func) []indVar {
                                if !inclusive {
                                        flags |= indVarMinExc
                                }
+                               flags |= indVarCountDown
                                step = -step
                        }
                        if f.pass.debug >= 1 {
@@ -285,6 +288,7 @@ func findIndVar(f *Func) []indVar {
 
                        iv = append(iv, indVar{
                                ind:   ind,
+                               nxt:   nxt,
                                min:   min,
                                max:   max,
                                entry: b.Succs[0].b,