cmd/compile: constant-fold loads from constant dictionaries and types

Update #59591

Change-Id: Id250a7779c5b53776fff73f3e678fec54d92a8e3
Reviewed-on: https://go-review.googlesource.com/c/go/+/486895
Reviewed-by: Cuong Manh Le <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Run-TryBot: Keith Randall <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>
Auto-Submit: Keith Randall <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: randall77

src/cmd/compile/internal/noder/reader.go

@@ -3988,7 +3988,7 @@ func setBasePos(pos src.XPos) {
 //
 // N.B., this variable name is known to Delve:
 // https://github.com/go-delve/delve/blob/cb91509630529e6055be845688fd21eb89ae8714/pkg/proc/eval.go#L28
-const dictParamName = ".dict"
+const dictParamName = typecheck.LocalDictName
 
 // shapeSig returns a copy of fn's signature, except adding a
 // dictionary parameter and promoting the receiver parameter (if any)

src/cmd/compile/internal/reflectdata/reflect.go

@@ -844,7 +844,14 @@ func TypeLinksymLookup(name string) *obj.LSym {
 }
 
 func TypeLinksym(t *types.Type) *obj.LSym {
-	return TypeSym(t).Linksym()
+	lsym := TypeSym(t).Linksym()
+	signatmu.Lock()
+	if lsym.Extra == nil {
+		ti := lsym.NewTypeInfo()
+		ti.Type = t
+	}
+	signatmu.Unlock()
+	return lsym
 }
 
 // Deprecated: Use TypePtrAt instead.
@@ -1878,7 +1885,9 @@ func MarkTypeUsedInInterface(t *types.Type, from *obj.LSym) {
 		// Shape types shouldn't be put in interfaces, so we shouldn't ever get here.
 		base.Fatalf("shape types have no methods %+v", t)
 	}
-	tsym := TypeLinksym(t)
+	MarkTypeSymUsedInInterface(TypeLinksym(t), from)
+}
+func MarkTypeSymUsedInInterface(tsym *obj.LSym, from *obj.LSym) {
 	// Emit a marker relocation. The linker will know the type is converted
 	// to an interface if "from" is reachable.
 	r := obj.Addrel(from)

src/cmd/compile/internal/ssa/_gen/generic.rules

@@ -2061,6 +2061,10 @@
 	&& warnRule(fe.Debug_checknil(), v, "removed nil check")
 	=> (Invalid)
 
+// Addresses of globals are always non-nil.
+(NilCheck          (Addr {_} (SB))    _) => (Invalid)
+(NilCheck (Convert (Addr {_} (SB)) _) _) => (Invalid)
+
 // for late-expanded calls, recognize memequal applied to a single constant byte
 // Support is limited by 1, 2, 4, 8 byte sizes
 (StaticLECall {callAux} sptr (Addr {scon} (SB)) (Const64 [1]) mem)
@@ -2148,6 +2152,8 @@
 (NeqPtr (OffPtr [o1] p1) (OffPtr [o2] p2)) && isSamePtr(p1, p2) => (ConstBool [o1 != o2])
 (EqPtr  (Const(32|64) [c]) (Const(32|64) [d])) => (ConstBool [c == d])
 (NeqPtr (Const(32|64) [c]) (Const(32|64) [d])) => (ConstBool [c != d])
+(EqPtr  (Convert (Addr {x} _) _) (Addr {y} _)) => (ConstBool [x==y])
+(NeqPtr (Convert (Addr {x} _) _) (Addr {y} _)) => (ConstBool [x!=y])
 
 (EqPtr  (LocalAddr _ _) (Addr _)) => (ConstBool [false])
 (EqPtr  (OffPtr (LocalAddr _ _)) (Addr _)) => (ConstBool [false])
@@ -2169,7 +2175,8 @@
 // Evaluate constant user nil checks.
 (IsNonNil (ConstNil)) => (ConstBool [false])
 (IsNonNil (Const(32|64) [c])) => (ConstBool [c != 0])
-(IsNonNil (Addr _)) => (ConstBool [true])
+(IsNonNil          (Addr _)   ) => (ConstBool [true])
+(IsNonNil (Convert (Addr _) _)) => (ConstBool [true])
 (IsNonNil (LocalAddr _ _)) => (ConstBool [true])
 
 // Inline small or disjoint runtime.memmove calls with constant length.
@@ -2212,11 +2219,7 @@
 	=> (Move {types.Types[types.TUINT8]} [int64(sz)] dst src mem)
 
 // De-virtualize late-expanded interface calls into late-expanded static calls.
-// Note that (ITab (IMake)) doesn't get rewritten until after the first opt pass,
-// so this rule should trigger reliably.
-// devirtLECall removes the first argument, adds the devirtualized symbol to the AuxCall, and changes the opcode
-(InterLECall [argsize] {auxCall} (Load (OffPtr [off] (ITab (IMake (Addr {itab} (SB)) _))) _) ___) && devirtLESym(v, auxCall, itab, off) !=
-    nil => devirtLECall(v, devirtLESym(v, auxCall, itab, off))
+(InterLECall [argsize] {auxCall} (Addr {fn} (SB)) ___) => devirtLECall(v, fn.(*obj.LSym))
 
 // Move and Zero optimizations.
 // Move source and destination may overlap.
@@ -2730,3 +2733,15 @@
 (RotateLeft(64|32|16|8) (RotateLeft(64|32|16|8) x c) d) && c.Type.Size() == 4 && d.Type.Size() == 4 => (RotateLeft(64|32|16|8) x (Add32 <c.Type> c d))
 (RotateLeft(64|32|16|8) (RotateLeft(64|32|16|8) x c) d) && c.Type.Size() == 2 && d.Type.Size() == 2 => (RotateLeft(64|32|16|8) x (Add16 <c.Type> c d))
 (RotateLeft(64|32|16|8) (RotateLeft(64|32|16|8) x c) d) && c.Type.Size() == 1 && d.Type.Size() == 1 => (RotateLeft(64|32|16|8) x (Add8  <c.Type> c d))
+
+// Loading constant values from dictionaries and itabs.
+(Load <t> (OffPtr [off]                       (Addr {s} sb)       ) _) && t.IsUintptr() && isFixedSym(s, off) => (Addr {fixedSym(b.Func, s, off)} sb)
+(Load <t> (OffPtr [off]              (Convert (Addr {s} sb) _)    ) _) && t.IsUintptr() && isFixedSym(s, off) => (Addr {fixedSym(b.Func, s, off)} sb)
+(Load <t> (OffPtr [off] (ITab (IMake          (Addr {s} sb)    _))) _) && t.IsUintptr() && isFixedSym(s, off) => (Addr {fixedSym(b.Func, s, off)} sb)
+(Load <t> (OffPtr [off] (ITab (IMake (Convert (Addr {s} sb) _) _))) _) && t.IsUintptr() && isFixedSym(s, off) => (Addr {fixedSym(b.Func, s, off)} sb)
+
+// Loading constant values from runtime._type.hash.
+(Load <t> (OffPtr [off]                       (Addr {sym} _)       ) _) && t.IsInteger() && t.Size() == 4 && isFixed32(config, sym, off) => (Const32 [fixed32(config, sym, off)])
+(Load <t> (OffPtr [off]              (Convert (Addr {sym} _) _)    ) _) && t.IsInteger() && t.Size() == 4 && isFixed32(config, sym, off) => (Const32 [fixed32(config, sym, off)])
+(Load <t> (OffPtr [off] (ITab (IMake          (Addr {sym} _)    _))) _) && t.IsInteger() && t.Size() == 4 && isFixed32(config, sym, off) => (Const32 [fixed32(config, sym, off)])
+(Load <t> (OffPtr [off] (ITab (IMake (Convert (Addr {sym} _) _) _))) _) && t.IsInteger() && t.Size() == 4 && isFixed32(config, sym, off) => (Const32 [fixed32(config, sym, off)])

src/cmd/compile/internal/ssa/rewrite.go

@@ -7,6 +7,7 @@ package ssa
 import (
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/logopt"
+	"cmd/compile/internal/reflectdata"
 	"cmd/compile/internal/types"
 	"cmd/internal/obj"
 	"cmd/internal/obj/s390x"
@@ -19,6 +20,7 @@ import (
 	"math/bits"
 	"os"
 	"path/filepath"
+	"strings"
 )
 
 type deadValueChoice bool
@@ -799,25 +801,6 @@ func loadLSymOffset(lsym *obj.LSym, offset int64) *obj.LSym {
 	return nil
 }
 
-// de-virtualize an InterLECall
-// 'sym' is the symbol for the itab.
-func devirtLESym(v *Value, aux Aux, sym Sym, offset int64) *obj.LSym {
-	n, ok := sym.(*obj.LSym)
-	if !ok {
-		return nil
-	}
-
-	lsym := loadLSymOffset(n, offset)
-	if f := v.Block.Func; f.pass.debug > 0 {
-		if lsym != nil {
-			f.Warnl(v.Pos, "de-virtualizing call")
-		} else {
-			f.Warnl(v.Pos, "couldn't de-virtualize call")
-		}
-	}
-	return lsym
-}
-
 func devirtLECall(v *Value, sym *obj.LSym) *Value {
 	v.Op = OpStaticLECall
 	auxcall := v.Aux.(*AuxCall)
@@ -827,6 +810,9 @@ func devirtLECall(v *Value, sym *obj.LSym) *Value {
 	copy(v.Args[0:], v.Args[1:])
 	v.Args[len(v.Args)-1] = nil // aid GC
 	v.Args = v.Args[:len(v.Args)-1]
+	if f := v.Block.Func; f.pass.debug > 0 {
+		f.Warnl(v.Pos, "de-virtualizing call")
+	}
 	return v
 }
 
@@ -1743,6 +1729,73 @@ func symIsROZero(sym Sym) bool {
 	return true
 }
 
+// isFixed32 returns true if the int32 at offset off in symbol sym
+// is known and constant.
+func isFixed32(c *Config, sym Sym, off int64) bool {
+	return isFixed(c, sym, off, 4)
+}
+
+// isFixed returns true if the range [off,off+size] of the symbol sym
+// is known and constant.
+func isFixed(c *Config, sym Sym, off, size int64) bool {
+	lsym := sym.(*obj.LSym)
+	if lsym.Extra == nil {
+		return false
+	}
+	if _, ok := (*lsym.Extra).(*obj.TypeInfo); ok {
+		if off == 2*c.PtrSize && size == 4 {
+			return true // type hash field
+		}
+	}
+	return false
+}
+func fixed32(c *Config, sym Sym, off int64) int32 {
+	lsym := sym.(*obj.LSym)
+	if ti, ok := (*lsym.Extra).(*obj.TypeInfo); ok {
+		if off == 2*c.PtrSize {
+			return int32(types.TypeHash(ti.Type.(*types.Type)))
+		}
+	}
+	base.Fatalf("fixed32 data not known for %s:%d", sym, off)
+	return 0
+}
+
+// isFixedSym returns true if the contents of sym at the given offset
+// is known and is the constant address of another symbol.
+func isFixedSym(sym Sym, off int64) bool {
+	lsym := sym.(*obj.LSym)
+	switch {
+	case lsym.Type == objabi.SRODATA:
+		// itabs, dictionaries
+	default:
+		return false
+	}
+	for _, r := range lsym.R {
+		if (r.Type == objabi.R_ADDR || r.Type == objabi.R_WEAKADDR) && int64(r.Off) == off && r.Add == 0 {
+			return true
+		}
+	}
+	return false
+}
+func fixedSym(f *Func, sym Sym, off int64) Sym {
+	lsym := sym.(*obj.LSym)
+	for _, r := range lsym.R {
+		if (r.Type == objabi.R_ADDR || r.Type == objabi.R_WEAKADDR) && int64(r.Off) == off {
+			if strings.HasPrefix(r.Sym.Name, "type:") {
+				// In case we're loading a type out of a dictionary, we need to record
+				// that the containing function might put that type in an interface.
+				// That information is currently recorded in relocations in the dictionary,
+				// but if we perform this load at compile time then the dictionary
+				// might be dead.
+				reflectdata.MarkTypeSymUsedInInterface(r.Sym, f.fe.Func().Linksym())
+			}
+			return r.Sym
+		}
+	}
+	base.Fatalf("fixedSym data not known for %s:%d", sym, off)
+	return nil
+}
+
 // read8 reads one byte from the read-only global sym at offset off.
 func read8(sym interface{}, off int64) uint8 {
 	lsym := sym.(*obj.LSym)