Go patch committed: Don't duplicate calls with multiple results

Go patch committed: Don't duplicate calls with multiple results

[Ian Lance Taylor]

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While moving expressions around to preserve the specified order of
evaluation, the Go frontend was duplicating call expressions with
multiple results.  This had no bad effect as the second instance
generated no code for the backend.  But, it's pointless and wasteful.
This patch by Than McIntosh fixes the problem.  This fixes
https://golang.org/issue/17237.  Bootstrapped and ran Go testsuite on
x86_64-pc-linux-gnu.  Committed to mainline.

Ian

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Index: gcc/go/gofrontend/MERGE
===================================================================
--- gcc/go/gofrontend/MERGE	(revision 240558)
+++ gcc/go/gofrontend/MERGE	(working copy)
@@ -1,4 +1,4 @@
-1d8d834b5eb9f683cc06529145b353bb5b08e7ea
+8aca265d317059ae6d9721a4a231895d80d0a82c
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
Index: gcc/go/gofrontend/gogo.cc
===================================================================
--- gcc/go/gofrontend/gogo.cc	(revision 240453)
+++ gcc/go/gofrontend/gogo.cc	(working copy)
@@ -3616,11 +3616,21 @@ Order_eval::statement(Block* block, size
 	  // be handled specially.  We can't create a temporary
 	  // because there is no type to give it.  Any actual uses of
 	  // the values will be done via Call_result_expressions.
-	  s = Statement::make_statement(*pexpr, true);
-	}
+          //
+          // Since a given call expression can be shared by multiple
+          // Call_result_expressions, avoid hoisting the call the
+          // second time we see it here.
+          if (this->remember_expression(*pexpr))
+            s = NULL;
+          else
+            s = Statement::make_statement(*pexpr, true);
+        }
 
-      block->insert_statement_before(*pindex, s);
-      ++*pindex;
+      if (s != NULL)
+        {
+          block->insert_statement_before(*pindex, s);
+          ++*pindex;
+        }
     }
 
   if (init != orig_init)
@@ -7949,13 +7959,14 @@ Traverse::remember_type(const Type* type
 }
 
 // Record that we are looking at an expression, and return true if we
-// have already seen it.
+// have already seen it. NB: this routine used to assert if the traverse
+// mask did not include expressions/types -- this is no longer the case,
+// since it can be useful to remember specific expressions during
+// walks that only cover statements.
 
 bool
 Traverse::remember_expression(const Expression* expression)
 {
-  go_assert((this->traverse_mask() & traverse_types) != 0
-	     || (this->traverse_mask() & traverse_expressions) != 0);
   if (this->expressions_seen_ == NULL)
     this->expressions_seen_ = new Expressions_seen();
   std::pair<Expressions_seen::iterator, bool> ins =