From 30166088e46389150ed2e766c1fb02bd3c0d8e6a Mon Sep 17 00:00:00 2001
From: Alan Donovan <adonovan@google.com>
Date: Wed, 11 Jun 2014 16:33:25 -0400
Subject: [PATCH] go/ssa: remove optimization of 'rundefers'.

The SSA builder shouldn't be in the business of
interprocedural optimization, especially in the presence of
concurrency.

This causes the instruction count to increase by 0.03%.

LGTM=gri
R=gri, pcc
CC=golang-codereviews
https://golang.org/cl/105020045
---
 go/ssa/builder.go | 19 +------------------
 go/ssa/util.go    | 16 ----------------
 2 files changed, 1 insertion(+), 34 deletions(-)

diff --git a/go/ssa/builder.go b/go/ssa/builder.go
index be55bdb67cf..fcf320edc7b 100644
--- a/go/ssa/builder.go
+++ b/go/ssa/builder.go
@@ -1918,24 +1918,7 @@ start:
 		// locals (which may be mutated by the deferred call)
 		// and return them.
 		if fn.namedResults != nil {
-			// Optimization: if we can prove the deferred call
-			// won't cause recovery from panic, we can avoid a
-			// Recover block.
-			// We scan the callee for calls to recover() iff:
-			// - it's a static call
-			// - to a function in the same package
-			//   (other packages' SSA building happens concurrently)
-			// - whose SSA building has started (Blocks != nil)
-			// - and finished (i.e. not this function)
-			// NB, this is always true for: defer func() { ... } ()
-			//
-			// TODO(adonovan): optimize interpackage cases, e.g.
-			//   (sync.Mutex).Unlock(), (io.Closer).Close
-			if callee, ok := v.Call.Value.(*Function); ok && callee.Pkg == fn.Pkg && callee != fn && callee.Blocks != nil && !callsRecover(callee) {
-				// Deferred call cannot cause recovery from panic.
-			} else {
-				createRecoverBlock(fn)
-			}
+			createRecoverBlock(fn)
 		}
 
 	case *ast.ReturnStmt:
diff --git a/go/ssa/util.go b/go/ssa/util.go
index 3c661c360c8..56220aba4ff 100644
--- a/go/ssa/util.go
+++ b/go/ssa/util.go
@@ -103,22 +103,6 @@ func logStack(format string, args ...interface{}) func() {
 	}
 }
 
-// callsRecover reports whether f contains a direct call to recover().
-func callsRecover(f *Function) bool {
-	for _, b := range f.Blocks {
-		for _, instr := range b.Instrs {
-			if call, ok := instr.(*Call); ok {
-				if blt, ok := call.Call.Value.(*Builtin); ok {
-					if blt.Name() == "recover" {
-						return true
-					}
-				}
-			}
-		}
-	}
-	return false
-}
-
 // newVar creates a 'var' for use in a types.Tuple.
 func newVar(name string, typ types.Type) *types.Var {
 	return types.NewParam(token.NoPos, nil, name, typ)