[dev.simd] cmd/compile: rewrite to elide Slicemask from len==c>0 slicing

This might have been something that prove could be educated
into figuring out, but this also works, and it also helps
prove downstream.

Adjusted the prove test, because this change moved a message.

Change-Id: I5eabe639eff5db9cd9766a6a8666fdb4973829cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/697715
Commit-Queue: David Chase <drchase@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Bypass: David Chase <drchase@google.com>

diff --git a/src/cmd/compile/internal/ssa/_gen/generic.rules b/src/cmd/compile/internal/ssa/_gen/generic.rules
index 00e8fcbe32ec75cee91345719dc169f63d01c051..8583cfae40c862955332a4de22bba1ff7b34941d 100644 (file)
--- a/src/cmd/compile/internal/ssa/_gen/generic.rules
+++ b/src/cmd/compile/internal/ssa/_gen/generic.rules
@@ -989,6 +989,10 @@
     (Const64 <typ.Int> [0])
     (Const64 <typ.Int> [0]))
 
+// Special rule to help constant slicing; len > 0 implies cap > 0 implies Slicemask is all 1
+(SliceMake (AddPtr <t> x (And64 y (Slicemask _))) w:(Const64 [c]) z) && c > 0 => (SliceMake (AddPtr <t> x y) w z)
+(SliceMake (AddPtr <t> x (And32 y (Slicemask _))) w:(Const32 [c]) z) && c > 0 => (SliceMake (AddPtr <t> x y) w z)
+
 // interface ops
 (ConstInterface) =>
   (IMake

diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index fe61ceaff2efcfe8489f1889f7002e10697e75f6..c9cff8651b76101c7fc1d4eef0455ba49e47eed5 100644 (file)
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -422,6 +422,8 @@ func rewriteValuegeneric(v *Value) bool {
                return rewriteValuegeneric_OpSliceCap(v)
        case OpSliceLen:
                return rewriteValuegeneric_OpSliceLen(v)
+       case OpSliceMake:
+               return rewriteValuegeneric_OpSliceMake(v)
        case OpSlicePtr:
                return rewriteValuegeneric_OpSlicePtr(v)
        case OpSlicemask:
@@ -30645,6 +30647,91 @@ func rewriteValuegeneric_OpSliceLen(v *Value) bool {
        }
        return false
 }
+func rewriteValuegeneric_OpSliceMake(v *Value) bool {
+       v_2 := v.Args[2]
+       v_1 := v.Args[1]
+       v_0 := v.Args[0]
+       b := v.Block
+       // match: (SliceMake (AddPtr <t> x (And64 y (Slicemask _))) w:(Const64 [c]) z)
+       // cond: c > 0
+       // result: (SliceMake (AddPtr <t> x y) w z)
+       for {
+               if v_0.Op != OpAddPtr {
+                       break
+               }
+               t := v_0.Type
+               _ = v_0.Args[1]
+               x := v_0.Args[0]
+               v_0_1 := v_0.Args[1]
+               if v_0_1.Op != OpAnd64 {
+                       break
+               }
+               _ = v_0_1.Args[1]
+               v_0_1_0 := v_0_1.Args[0]
+               v_0_1_1 := v_0_1.Args[1]
+               for _i0 := 0; _i0 <= 1; _i0, v_0_1_0, v_0_1_1 = _i0+1, v_0_1_1, v_0_1_0 {
+                       y := v_0_1_0
+                       if v_0_1_1.Op != OpSlicemask {
+                               continue
+                       }
+                       w := v_1
+                       if w.Op != OpConst64 {
+                               continue
+                       }
+                       c := auxIntToInt64(w.AuxInt)
+                       z := v_2
+                       if !(c > 0) {
+                               continue
+                       }
+                       v.reset(OpSliceMake)
+                       v0 := b.NewValue0(v.Pos, OpAddPtr, t)
+                       v0.AddArg2(x, y)
+                       v.AddArg3(v0, w, z)
+                       return true
+               }
+               break
+       }
+       // match: (SliceMake (AddPtr <t> x (And32 y (Slicemask _))) w:(Const32 [c]) z)
+       // cond: c > 0
+       // result: (SliceMake (AddPtr <t> x y) w z)
+       for {
+               if v_0.Op != OpAddPtr {
+                       break
+               }
+               t := v_0.Type
+               _ = v_0.Args[1]
+               x := v_0.Args[0]
+               v_0_1 := v_0.Args[1]
+               if v_0_1.Op != OpAnd32 {
+                       break
+               }
+               _ = v_0_1.Args[1]
+               v_0_1_0 := v_0_1.Args[0]
+               v_0_1_1 := v_0_1.Args[1]
+               for _i0 := 0; _i0 <= 1; _i0, v_0_1_0, v_0_1_1 = _i0+1, v_0_1_1, v_0_1_0 {
+                       y := v_0_1_0
+                       if v_0_1_1.Op != OpSlicemask {
+                               continue
+                       }
+                       w := v_1
+                       if w.Op != OpConst32 {
+                               continue
+                       }
+                       c := auxIntToInt32(w.AuxInt)
+                       z := v_2
+                       if !(c > 0) {
+                               continue
+                       }
+                       v.reset(OpSliceMake)
+                       v0 := b.NewValue0(v.Pos, OpAddPtr, t)
+                       v0.AddArg2(x, y)
+                       v.AddArg3(v0, w, z)
+                       return true
+               }
+               break
+       }
+       return false
+}
 func rewriteValuegeneric_OpSlicePtr(v *Value) bool {
        v_0 := v.Args[0]
        // match: (SlicePtr (SliceMake (SlicePtr x) _ _))

diff --git a/test/prove.go b/test/prove.go
index 70a27865cfd7c32805a5edeee173bd9fa5c0badc..6d2bb0962be89471ead55c1065da0114fc34fe4f 100644 (file)
--- a/test/prove.go
+++ b/test/prove.go
@@ -511,10 +511,10 @@ func f19() (e int64, err error) {
 
 func sm1(b []int, x int) {
        // Test constant argument to slicemask.
-       useSlice(b[2:8]) // ERROR "Proved slicemask not needed$"
+       useSlice(b[2:8]) // optimized away earlier by rewrite
        // Test non-constant argument with known limits.
        if cap(b) > 10 {
-               useSlice(b[2:])
+               useSlice(b[2:]) // ERROR "Proved slicemask not needed$"
        }
 }