cmd/compile: correct leaf type when "selecting" singleton register-sized struct

Two part fix:
1) bring the type "correction" forward from a later CL in the expand calls series
2) when a leaf-selwect is rewritten in place, update the type (it might have been
   changed by the type correction in 1).

Fixes #41736.

Change-Id: Id097efd10481bf0ad92aaead81a7207221c144b5
Reviewed-on: https://go-review.googlesource.com/c/go/+/259203
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

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

@@ -195,7 +195,7 @@ const (
 	ClassParamOut                     // return value
 )
 
-const go116lateCallExpansion = false
+const go116lateCallExpansion = true
 
 // LateCallExpansionEnabledWithin returns true if late call expansion should be tested
 // within compilation of a function/method triggered by GOSSAHASH (defaults to "yes").

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

@@ -58,6 +58,29 @@ func expandCalls(f *Func) {
 		return t.IsStruct() || t.IsArray() || regSize == 4 && t.Size() > 4 && t.IsInteger()
 	}
 
+	// removeTrivialWrapperTypes unwraps layers of
+	// struct { singleField SomeType } and [1]SomeType
+	// until a non-wrapper type is reached.  This is useful
+	// for working with assignments to/from interface data
+	// fields (either second operand to OpIMake or OpIData)
+	// where the wrapping or type conversion can be elided
+	// because of type conversions/assertions in source code
+	// that do not appear in SSA.
+	removeTrivialWrapperTypes := func(t *types.Type) *types.Type {
+		for {
+			if t.IsStruct() && t.NumFields() == 1 {
+				t = t.Field(0).Type
+				continue
+			}
+			if t.IsArray() && t.NumElem() == 1 {
+				t = t.Elem()
+				continue
+			}
+			break
+		}
+		return t
+	}
+
 	// Calls that need lowering have some number of inputs, including a memory input,
 	// and produce a tuple of (value1, value2, ..., mem) where valueK may or may not be SSA-able.
 
@@ -84,7 +107,7 @@ func expandCalls(f *Func) {
 				// rewrite v as a Copy of call -- the replacement call will produce a mem.
 				leaf.copyOf(call)
 			} else {
-				leafType := leaf.Type
+				leafType := removeTrivialWrapperTypes(leaf.Type)
 				pt := types.NewPtr(leafType)
 				if canSSAType(leafType) {
 					off := f.ConstOffPtrSP(pt, offset+aux.OffsetOfResult(which), sp)
@@ -92,6 +115,7 @@ func expandCalls(f *Func) {
 					if leaf.Block == call.Block {
 						leaf.reset(OpLoad)
 						leaf.SetArgs2(off, call)
+						leaf.Type = leafType
 					} else {
 						w := call.Block.NewValue2(leaf.Pos, OpLoad, leafType, off, call)
 						leaf.copyOf(w)
@@ -192,6 +216,13 @@ func expandCalls(f *Func) {
 
 		case types.TARRAY:
 			elt := t.Elem()
+			if src.Op == OpIData && t.NumElem() == 1 && t.Width == regSize && elt.Width == regSize {
+				t = removeTrivialWrapperTypes(t)
+				if t.Etype == types.TSTRUCT || t.Etype == types.TARRAY {
+					f.Fatalf("Did not expect to find IDATA-immediate with non-trivial struct/array in it")
+				}
+				break // handle the leaf type.
+			}
 			for i := int64(0); i < t.NumElem(); i++ {
 				sel := src.Block.NewValue1I(pos, OpArraySelect, elt, i, src)
 				mem = splitStore(dst, sel, mem, v, elt, offset+i*elt.Width, firstStorePos)
@@ -199,7 +230,7 @@ func expandCalls(f *Func) {
 			}
 			return mem
 		case types.TSTRUCT:
-			if src.Op == OpIData && t.NumFields() == 1 && t.Field(0).Type.Width == t.Width && t.Width == regSize   {
+			if src.Op == OpIData && t.NumFields() == 1 && t.Field(0).Type.Width == t.Width && t.Width == regSize {
 				// This peculiar test deals with accesses to immediate interface data.
 				// It works okay because everything is the same size.
 				// Example code that triggers this can be found in go/constant/value.go, function ToComplex
@@ -207,11 +238,9 @@ func expandCalls(f *Func) {
 				// v121 (+882) = StaticLECall <floatVal,mem> {AuxCall{"".itof([intVal,0])[floatVal,8]}} [16] v119 v1
 				// This corresponds to the generic rewrite rule "(StructSelect [0] (IData x)) => (IData x)"
 				// Guard against "struct{struct{*foo}}"
-				for t.Etype == types.TSTRUCT && t.NumFields() == 1 {
-					t = t.Field(0).Type
-				}
+				t = removeTrivialWrapperTypes(t)
 				if t.Etype == types.TSTRUCT || t.Etype == types.TARRAY {
-					f.Fatalf("Did not expect to find IDATA-immediate with non-trivial struct in it")
+					f.Fatalf("Did not expect to find IDATA-immediate with non-trivial struct/array in it")
 				}
 				break // handle the leaf type.
 			}

test/fixedbugs/issue41736.go

@@ -0,0 +1,105 @@
+// compile
+
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type I struct {
+	x int64
+}
+
+type F struct {
+	x float64
+}
+
+type C struct {
+	x *complex128
+}
+
+type D struct {
+	x complex64
+}
+
+type A [1]*complex128
+
+//go:noinline
+func (i I) X() C {
+	cx := complex(0, float64(i.x))
+	return C{&cx}
+}
+
+//go:noinline
+func (f F) X() C {
+	cx := complex(f.x, 0)
+	return C{&cx}
+}
+
+//go:noinline
+func (c C) X() C {
+	cx := complex(imag(*c.x), real(*c.x))
+	return C{&cx}
+}
+
+//go:noinline
+func (d D) X() C {
+	cx := complex(float64(imag(d.x)), -float64(real(d.x)))
+	return C{&cx}
+}
+
+//go:noinline
+func (a A) X() C {
+	cx := complex(-float64(imag(*a[0])), float64(real(*a[0])))
+	return C{&cx}
+}
+
+//go:noinline
+func (i I) id() I {
+	return i
+}
+
+//go:noinline
+func (f F) id() F {
+	return f
+}
+
+//go:noinline
+func (c C) id() C {
+	return c
+}
+
+//go:noinline
+func (d D) id() D {
+	return d
+}
+
+//go:noinline
+func (a A) id() A {
+	return a
+}
+
+type T interface {
+	X() C
+}
+
+func G(x []T) []T {
+	var y []T
+	for _, a := range x {
+		var v T
+		switch u := a.(type) {
+		case I:
+			v = u.id()
+		case F:
+			v = u.id()
+		case C:
+			v = u.id()
+		case D:
+			v = u.id()
+		case A:
+			v = u.id()
+		}
+		y = append(y, v)
+	}
+	return y
+}