compiler: eliminate bound checks in append expression

    
    The compiler generates two array index expressions when lowering
    an append expression. Currently they generate bound checks.
    Bound checks are not necessary in this case, as we know the slice
    has, or will grow to, enough length and capacity. Eliminate them.
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/166817

From-SVN: r269699

3 files changed, 99 insertions, 77 deletions

diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index f3c52bf..61bcab2 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -1,4 +1,4 @@
-946aa5ab2e82d045a2a3b2f18ba2c5b00e957c4b
+80a7f6dae0861a06407a44c501b6346a4abd119c
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
diff --git a/gcc/go/gofrontend/expressions.cc b/gcc/go/gofrontend/expressions.cc
index f32b7a4..f41647a 100644
--- a/gcc/go/gofrontend/expressions.cc
+++ b/gcc/go/gofrontend/expressions.cc
@@ -8008,8 +8008,8 @@ Builtin_call_expression::flatten_append(Gogo* gogo, Named_object* function,
   ref = Expression::make_temporary_reference(s1tmp, loc);
   Expression* zero = Expression::make_integer_ul(0, int_type, loc);
   Expression* ref2 = Expression::make_temporary_reference(ntmp, loc);
-  // FIXME: Mark this index as not requiring bounds checks.
-  ref = Expression::make_index(ref, zero, ref2, NULL, loc);
+  ref = Expression::make_array_index(ref, zero, ref2, NULL, loc);
+  ref->array_index_expression()->set_needs_bounds_check(false);
 
   if (assign_lhs == NULL)
     {
@@ -8058,8 +8058,8 @@ Builtin_call_expression::flatten_append(Gogo* gogo, Named_object* function,
       a1 = Expression::make_temporary_reference(s1tmp, loc);
       ref = Expression::make_temporary_reference(l1tmp, loc);
       Expression* nil = Expression::make_nil(loc);
-      // FIXME: Mark this index as not requiring bounds checks.
-      a1 = Expression::make_index(a1, ref, nil, NULL, loc);
+      a1 = Expression::make_array_index(a1, ref, nil, NULL, loc);
+      a1->array_index_expression()->set_needs_bounds_check(false);
 
       a2 = Expression::make_temporary_reference(s2tmp, loc);
 
@@ -8086,9 +8086,9 @@ Builtin_call_expression::flatten_append(Gogo* gogo, Named_object* function,
 	  ref2 = Expression::make_temporary_reference(l1tmp, loc);
 	  Expression* off = Expression::make_integer_ul(i, int_type, loc);
 	  ref2 = Expression::make_binary(OPERATOR_PLUS, ref2, off, loc);
-	  // FIXME: Mark this index as not requiring bounds checks.
-	  Expression* lhs = Expression::make_index(ref, ref2, NULL, NULL,
-						   loc);
+	  Expression* lhs = Expression::make_array_index(ref, ref2, NULL,
+                                                         NULL, loc);
+          lhs->array_index_expression()->set_needs_bounds_check(false);
 	  gogo->lower_expression(function, inserter, &lhs);
 	  gogo->flatten_expression(function, inserter, &lhs);
 	  // The flatten pass runs after the write barrier pass, so we
@@ -11328,15 +11328,6 @@ Array_index_expression::do_get_backend(Translate_context* context)
   if (length == NULL)
     length = cap_arg;
 
-  int code = (array_type->length() != NULL
-	      ? (this->end_ == NULL
-		 ? RUNTIME_ERROR_ARRAY_INDEX_OUT_OF_BOUNDS
-		 : RUNTIME_ERROR_ARRAY_SLICE_OUT_OF_BOUNDS)
-	      : (this->end_ == NULL
-		 ? RUNTIME_ERROR_SLICE_INDEX_OUT_OF_BOUNDS
-		 : RUNTIME_ERROR_SLICE_SLICE_OUT_OF_BOUNDS));
-  Bexpression* crash = gogo->runtime_error(code, loc)->get_backend(context);
-
   if (this->start_->type()->integer_type() == NULL
       && !Type::are_convertible(int_type, this->start_->type(), NULL))
     {
@@ -11344,31 +11335,46 @@ Array_index_expression::do_get_backend(Translate_context* context)
       return context->backend()->error_expression();
     }
 
-  Bexpression* bad_index =
-    Expression::check_bounds(this->start_, loc)->get_backend(context);
-
   Bexpression* start = this->start_->get_backend(context);
   start = gogo->backend()->convert_expression(int_btype, start, loc);
-  Bexpression* start_too_large =
-    gogo->backend()->binary_expression((this->end_ == NULL
-					? OPERATOR_GE
-					: OPERATOR_GT),
-                                       start,
-				       (this->end_ == NULL
-					? length
-					: capacity),
-                                       loc);
-  bad_index = gogo->backend()->binary_expression(OPERATOR_OROR, start_too_large,
-						 bad_index, loc);
+
+  Bexpression* crash = NULL;
+  Bexpression* bad_index = NULL;
+  if (this->needs_bounds_check_)
+    {
+      int code = (array_type->length() != NULL
+                  ? (this->end_ == NULL
+                     ? RUNTIME_ERROR_ARRAY_INDEX_OUT_OF_BOUNDS
+                     : RUNTIME_ERROR_ARRAY_SLICE_OUT_OF_BOUNDS)
+                  : (this->end_ == NULL
+                     ? RUNTIME_ERROR_SLICE_INDEX_OUT_OF_BOUNDS
+                     : RUNTIME_ERROR_SLICE_SLICE_OUT_OF_BOUNDS));
+      crash = gogo->runtime_error(code, loc)->get_backend(context);
+      bad_index = Expression::check_bounds(this->start_, loc)->get_backend(context);
+      Bexpression* start_too_large =
+        gogo->backend()->binary_expression((this->end_ == NULL
+                                            ? OPERATOR_GE
+                                            : OPERATOR_GT),
+                                           start,
+                                           (this->end_ == NULL
+                                            ? length
+                                            : capacity),
+                                           loc);
+      bad_index = gogo->backend()->binary_expression(OPERATOR_OROR,
+                                                     start_too_large,
+                                                     bad_index, loc);
+    }
+
 
   Bfunction* bfn = context->function()->func_value()->get_decl();
   if (this->end_ == NULL)
     {
       // Simple array indexing.  This has to return an l-value, so
       // wrap the index check into START.
-      start =
-        gogo->backend()->conditional_expression(bfn, int_btype, bad_index,
-						crash, start, loc);
+      if (this->needs_bounds_check_)
+        start =
+          gogo->backend()->conditional_expression(bfn, int_btype, bad_index,
+                                                  crash, start, loc);
 
       Bexpression* ret;
       if (array_type->length() != NULL)
@@ -11396,22 +11402,26 @@ Array_index_expression::do_get_backend(Translate_context* context)
 
   if (this->cap_ != NULL)
     {
-      Bexpression* bounds_bcheck =
-	Expression::check_bounds(this->cap_, loc)->get_backend(context);
-      bad_index =
-	gogo->backend()->binary_expression(OPERATOR_OROR, bounds_bcheck,
-					   bad_index, loc);
       cap_arg = gogo->backend()->convert_expression(int_btype, cap_arg, loc);
 
-      Bexpression* cap_too_small =
-	gogo->backend()->binary_expression(OPERATOR_LT, cap_arg, start, loc);
-      Bexpression* cap_too_large =
-	gogo->backend()->binary_expression(OPERATOR_GT, cap_arg, capacity, loc);
-      Bexpression* bad_cap =
-	gogo->backend()->binary_expression(OPERATOR_OROR, cap_too_small,
-					   cap_too_large, loc);
-      bad_index = gogo->backend()->binary_expression(OPERATOR_OROR, bad_cap,
-						     bad_index, loc);
+      if (this->needs_bounds_check_)
+        {
+          Bexpression* bounds_bcheck =
+            Expression::check_bounds(this->cap_, loc)->get_backend(context);
+          bad_index =
+            gogo->backend()->binary_expression(OPERATOR_OROR, bounds_bcheck,
+                                               bad_index, loc);
+
+          Bexpression* cap_too_small =
+            gogo->backend()->binary_expression(OPERATOR_LT, cap_arg, start, loc);
+          Bexpression* cap_too_large =
+            gogo->backend()->binary_expression(OPERATOR_GT, cap_arg, capacity, loc);
+          Bexpression* bad_cap =
+            gogo->backend()->binary_expression(OPERATOR_OROR, cap_too_small,
+                                               cap_too_large, loc);
+          bad_index = gogo->backend()->binary_expression(OPERATOR_OROR, bad_cap,
+                                                         bad_index, loc);
+        }
     }
 
   Bexpression* end;
@@ -11419,24 +11429,26 @@ Array_index_expression::do_get_backend(Translate_context* context)
     end = length;
   else
     {
-      Bexpression* bounds_bcheck =
-	Expression::check_bounds(this->end_, loc)->get_backend(context);
-
-      bad_index =
-	gogo->backend()->binary_expression(OPERATOR_OROR, bounds_bcheck,
-					   bad_index, loc);
-
       end = this->end_->get_backend(context);
       end = gogo->backend()->convert_expression(int_btype, end, loc);
-      Bexpression* end_too_small =
-	gogo->backend()->binary_expression(OPERATOR_LT, end, start, loc);
-      Bexpression* end_too_large =
-	gogo->backend()->binary_expression(OPERATOR_GT, end, cap_arg, loc);
-      Bexpression* bad_end =
-	gogo->backend()->binary_expression(OPERATOR_OROR, end_too_small,
-					   end_too_large, loc);
-      bad_index = gogo->backend()->binary_expression(OPERATOR_OROR, bad_end,
-						     bad_index, loc);
+      if (this->needs_bounds_check_)
+        {
+          Bexpression* bounds_bcheck =
+            Expression::check_bounds(this->end_, loc)->get_backend(context);
+          bad_index =
+            gogo->backend()->binary_expression(OPERATOR_OROR, bounds_bcheck,
+                                               bad_index, loc);
+
+          Bexpression* end_too_small =
+            gogo->backend()->binary_expression(OPERATOR_LT, end, start, loc);
+          Bexpression* end_too_large =
+            gogo->backend()->binary_expression(OPERATOR_GT, end, cap_arg, loc);
+          Bexpression* bad_end =
+            gogo->backend()->binary_expression(OPERATOR_OROR, end_too_small,
+                                               end_too_large, loc);
+          bad_index = gogo->backend()->binary_expression(OPERATOR_OROR, bad_end,
+                                                         bad_index, loc);
+        }
     }
 
   Bexpression* result_length =
@@ -11468,10 +11480,12 @@ Array_index_expression::do_get_backend(Translate_context* context)
   init.push_back(result_length);
   init.push_back(result_capacity);
 
-  Bexpression* ctor =
+  Bexpression* ret =
     gogo->backend()->constructor_expression(struct_btype, init, loc);
-  return gogo->backend()->conditional_expression(bfn, struct_btype, bad_index,
-						 crash, ctor, loc);
+  if (this->needs_bounds_check_)
+    ret = gogo->backend()->conditional_expression(bfn, struct_btype, bad_index,
+                                                  crash, ret, loc);
+  return ret;
 }
 
 // Dump ast representation for an array index expression.
diff --git a/gcc/go/gofrontend/expressions.h b/gcc/go/gofrontend/expressions.h
index 5d61b69..c521d9b 100644
--- a/gcc/go/gofrontend/expressions.h
+++ b/gcc/go/gofrontend/expressions.h
@@ -2854,7 +2854,7 @@ class Array_index_expression : public Expression
 			 Expression* end, Expression* cap, Location location)
     : Expression(EXPRESSION_ARRAY_INDEX, location),
       array_(array), start_(start), end_(end), cap_(cap), type_(NULL),
-      is_lvalue_(false)
+      is_lvalue_(false), needs_bounds_check_(true)
   { }
 
   // Return the array.
@@ -2898,6 +2898,10 @@ class Array_index_expression : public Expression
   set_is_lvalue()
   { this->is_lvalue_ = true; }
 
+  void
+  set_needs_bounds_check(bool b)
+  { this->needs_bounds_check_ = b; }
+
  protected:
   int
   do_traverse(Traverse*);
@@ -2917,15 +2921,17 @@ class Array_index_expression : public Expression
   Expression*
   do_copy()
   {
-    return Expression::make_array_index(this->array_->copy(),
-					this->start_->copy(),
-					(this->end_ == NULL
-					 ? NULL
-					 : this->end_->copy()),
-					(this->cap_ == NULL
-					 ? NULL
-					 : this->cap_->copy()),
-					this->location());
+    Expression* ret = Expression::make_array_index(this->array_->copy(),
+                                                   this->start_->copy(),
+                                                   (this->end_ == NULL
+                                                    ? NULL
+                                                    : this->end_->copy()),
+                                                   (this->cap_ == NULL
+                                                    ? NULL
+                                                    : this->cap_->copy()),
+                                                   this->location());
+    ret->array_index_expression()->set_needs_bounds_check(this->needs_bounds_check_);
+    return ret;
   }
 
   bool
@@ -2962,6 +2968,8 @@ class Array_index_expression : public Expression
   Type* type_;
   // Whether expr appears in an lvalue context.
   bool is_lvalue_;
+  // Whether bounds check is needed.
+  bool needs_bounds_check_;
 };
 
 // A string index.  This is used for both indexing and slicing.