cmd/compile: handle string concatenation in static init inliner

Static init inliner is using typecheck.EvalConst to handle string
concatenation expressions. But static init inliner may reveal constant
expressions after substitution, and the compiler needs to evaluate those
expressions in non-constant semantic. Using typecheck.EvalConst, which
always evaluates expressions in constant semantic, is not the right
choice.

For safety, this CL fold the logic to handle string concatenation to
static init inliner, so there won't be regression in handling constant
expressions in non-constant semantic. And also, future CL can simplify
typecheck.EvalConst logic.

Updates #58293
Updates #58339
Fixes #58439

Change-Id: I74068d99c245938e576afe9460cbd2b39677bbff
Reviewed-on: https://go-review.googlesource.com/c/go/+/466277
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 59 insertions, 5 deletions

diff --git a/src/cmd/compile/internal/staticinit/sched.go b/src/cmd/compile/internal/staticinit/sched.go
index c9b0239465..e5f7be4c5f 100644
--- a/src/cmd/compile/internal/staticinit/sched.go
+++ b/src/cmd/compile/internal/staticinit/sched.go
@@ -9,6 +9,7 @@ import (
 	"go/constant"
 	"go/token"
 	"os"
+	"strings"
 
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/ir"
@@ -866,14 +867,22 @@ func subst(n ir.Node, m map[*ir.Name]ir.Node) (ir.Node, bool) {
 		}
 		x = ir.Copy(x)
 		ir.EditChildrenWithHidden(x, edit)
-		if x, ok := x.(*ir.ConvExpr); ok && x.X.Op() == ir.OLITERAL {
-			if x, ok := truncate(x.X, x.Type()); ok {
+
+		// TODO: handle more operations, see details discussion in go.dev/cl/466277.
+		switch x.Op() {
+		case ir.OCONV:
+			x := x.(*ir.ConvExpr)
+			if x.X.Op() == ir.OLITERAL {
+				if x, ok := truncate(x.X, x.Type()); ok {
+					return x
+				}
+				valid = false
 				return x
 			}
-			valid = false
-			return x
+		case ir.OADDSTR:
+			return addStr(x.(*ir.AddStringExpr))
 		}
-		return typecheck.EvalConst(x)
+		return x
 	}
 	n = edit(n)
 	return n, valid
@@ -909,6 +918,51 @@ func truncate(c ir.Node, t *types.Type) (ir.Node, bool) {
 	return c, true
 }
 
+func addStr(n *ir.AddStringExpr) ir.Node {
+	// Merge adjacent constants in the argument list.
+	s := n.List
+	need := 0
+	for i := 0; i < len(s); i++ {
+		if i == 0 || !ir.IsConst(s[i-1], constant.String) || !ir.IsConst(s[i], constant.String) {
+			// Can't merge s[i] into s[i-1]; need a slot in the list.
+			need++
+		}
+	}
+	if need == len(s) {
+		return n
+	}
+	if need == 1 {
+		var strs []string
+		for _, c := range s {
+			strs = append(strs, ir.StringVal(c))
+		}
+		return typecheck.OrigConst(n, constant.MakeString(strings.Join(strs, "")))
+	}
+	newList := make([]ir.Node, 0, need)
+	for i := 0; i < len(s); i++ {
+		if ir.IsConst(s[i], constant.String) && i+1 < len(s) && ir.IsConst(s[i+1], constant.String) {
+			// merge from i up to but not including i2
+			var strs []string
+			i2 := i
+			for i2 < len(s) && ir.IsConst(s[i2], constant.String) {
+				strs = append(strs, ir.StringVal(s[i2]))
+				i2++
+			}
+
+			nl := ir.Copy(n).(*ir.AddStringExpr)
+			nl.List = s[i:i2]
+			newList = append(newList, typecheck.OrigConst(nl, constant.MakeString(strings.Join(strs, ""))))
+			i = i2 - 1
+		} else {
+			newList = append(newList, s[i])
+		}
+	}
+
+	nn := ir.Copy(n).(*ir.AddStringExpr)
+	nn.List = newList
+	return nn
+}
+
 const wrapGlobalMapInitSizeThreshold = 20
 
 // tryWrapGlobalMapInit examines the node 'n' to see if it is a map