compiler: add an option to emit optimization diagnostics

Add a -fgo-debug-optimization option to emit optimization
    diagnostics. This can be used for testing optimizations. Apply
    this to the range clear optimizations of maps and arrays.
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/170002

gcc/go:

	* lang.opt (-fgo-debug-optimization): New option.
	* go-c.h (struct go_create_gogo_args): Add debug_optimization
	field.
	* go-lang.c (go_langhook_init): Set debug_optimization field.
	* gccgo.texi (Invoking gccgo): Document -fgo-debug-optimization.

gcc/testsuite:

	* go.dg/arrayclear.go: New test.
	* go.dg/mapclear.go: New test.

From-SVN: r270993

gcc/go/ChangeLog

@@ -1,3 +1,11 @@
+2019-05-07  Cherry Zhang  <cherryyz@google.com>
+
+	* lang.opt (-fgo-debug-optimization): New option.
+	* go-c.h (struct go_create_gogo_args): Add debug_optimization
+	field.
+	* go-lang.c (go_langhook_init): Set debug_optimization field.
+	* gccgo.texi (Invoking gccgo): Document -fgo-debug-optimization.
+
 2019-03-06  Ian Lance Taylor  <iant@golang.org>
 
 	PR go/89227

gcc/go/gccgo.texi

@@ -246,6 +246,11 @@ This runs escape analysis only on functions whose names hash to values
 that match the given suffix @var{n}.  This can be used to binary
 search across functions to uncover escape analysis bugs.
 
+@item -fgo-debug-optimization
+@cindex @option{-fgo-debug-optimization}
+@cindex @option{-fno-go-debug-optimization}
+Output optimization diagnostics.
+
 @item -fgo-c-header=@var{file}
 @cindex @option{-fgo-c-header}
 Write top-level named Go struct definitions to @var{file} as C code.

gcc/go/go-c.h

@@ -49,6 +49,7 @@ struct go_create_gogo_args
   int debug_escape_level;
   const char* debug_escape_hash;
   int64_t nil_check_size_threshold;
+  bool debug_optimization;
 };
 
 extern void go_create_gogo (const struct go_create_gogo_args*);

gcc/go/go-lang.c

@@ -118,6 +118,7 @@ go_langhook_init (void)
   args.debug_escape_level = go_debug_escape_level;
   args.debug_escape_hash = go_debug_escape_hash;
   args.nil_check_size_threshold = TARGET_AIX ? -1 : 4096;
+  args.debug_optimization = go_debug_optimization;
   args.linemap = go_get_linemap();
   args.backend = go_get_backend();
   go_create_gogo (&args);

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-4b3015de639cf22ed11ff96097555700909827c8
+dc9c1b43753f392fdc2045bcb7a4abaa44fe79f1
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/go.cc

@@ -44,6 +44,8 @@ go_create_gogo(const struct go_create_gogo_args* args)
   if (args->debug_escape_hash != NULL)
     ::gogo->set_debug_escape_hash(args->debug_escape_hash);
   ::gogo->set_nil_check_size_threshold(args->nil_check_size_threshold);
+  if (args->debug_optimization)
+    ::gogo->set_debug_optimization(args->debug_optimization);
 }
 
 // Parse the input files.

gcc/go/gofrontend/gogo.cc

@@ -55,6 +55,7 @@ Gogo::Gogo(Backend* backend, Linemap* linemap, int, int pointer_size)
     check_divide_overflow_(true),
     compiling_runtime_(false),
     debug_escape_level_(0),
+    debug_optimization_(false),
     nil_check_size_threshold_(4096),
     verify_types_(),
     interface_types_(),

gcc/go/gofrontend/gogo.h

@@ -326,6 +326,16 @@ class Gogo
   set_debug_escape_hash(const std::string& s)
   { this->debug_escape_hash_ = s; }
 
+  // Return whether to output optimization diagnostics.
+  bool
+  debug_optimization() const
+  { return this->debug_optimization_; }
+
+  // Set the option to output optimization diagnostics.
+  void
+  set_debug_optimization(bool b)
+  { this->debug_optimization_ = b; }
+
   // Return the size threshold used to determine whether to issue
   // a nil-check for a given pointer dereference. A threshold of -1
   // implies that all potentially faulting dereference ops should
@@ -1075,6 +1085,9 @@ class Gogo
   // -fgo-debug-escape-hash option. The analysis is run only on
   // functions with names that hash to the matching value.
   std::string debug_escape_hash_;
+  // Whether to output optimization diagnostics, from the
+  // -fgo-debug-optimization option.
+  bool debug_optimization_;
   // Nil-check size threshhold.
   int64_t nil_check_size_threshold_;
   // A list of types to verify.

gcc/go/gofrontend/statements.cc

@@ -5512,6 +5512,8 @@ For_range_statement::do_lower(Gogo* gogo, Named_object*, Block* enclosing,
                                                      range_temp, loc);
       if (clear != NULL)
         {
+          if (gogo->debug_optimization())
+            go_inform(loc, "map range clear");
           temp_block->add_statement(clear);
           return Statement::make_block_statement(temp_block, loc);
         }
@@ -5527,6 +5529,8 @@ For_range_statement::do_lower(Gogo* gogo, Named_object*, Block* enclosing,
                                                        range_temp, loc);
       if (clear != NULL)
         {
+          if (gogo->debug_optimization())
+            go_inform(loc, "array range clear");
           temp_block->add_statement(clear);
           return Statement::make_block_statement(temp_block, loc);
         }

gcc/go/lang.opt

@@ -85,6 +85,10 @@ fgo-debug-escape-hash=
 Go Joined RejectNegative Var(go_debug_escape_hash) Init(0)
 -fgo-debug-escape-hash=<string>	Hash value to debug escape analysis.
 
+fgo-debug-optimization
+Go Var(go_debug_optimization) Init(0)
+Emit optimization diagnostics.
+
 o
 Go Joined Separate
 ; Documented in common.opt

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2019-05-07  Cherry Zhang  <cherryyz@google.com>
+
+	* go.dg/arrayclear.go: New test.
+	* go.dg/mapclear.go: New test.
+
 2019-05-07  Kelvin Nilsen  <kelvin@gcc.gnu.org>
 
 	PR target/89765

gcc/testsuite/go.dg/arrayclear.go

@@ -0,0 +1,20 @@
+// { dg-do compile }
+// { dg-options "-fgo-debug-optimization" }
+
+package p
+
+var a [10]int
+
+func arrayClear() {
+	for i := range a { // { dg-error "array range clear" }
+		a[i] = 0
+	}
+}
+
+var s []int
+
+func sliceClear() {
+	for i := range s { // { dg-error "array range clear" }
+		s[i] = 0
+	}
+}

gcc/testsuite/go.dg/mapclear.go

@@ -0,0 +1,10 @@
+// { dg-do compile }
+// { dg-options "-fgo-debug-optimization" }
+
+package p
+
+func clear(m map[int]int) {
+	for k := range m { // { dg-error "map range clear" }
+		delete(m, k)
+	}
+}