#SW2600

[Stan Cox <scox at redhat dot com>]

Here is a proposed patch for the array index piece of #SW2600 (should
optimize away assignments in other contexts).  For example: arr2[i = 1]
= 10 can potentially become arr2[1] = 10



diff --git a/elaborate.cxx b/elaborate.cxx
index 306baff..5f148f6 100644
--- a/elaborate.cxx
+++ b/elaborate.cxx
@@ -1690,6 +1690,8 @@ struct dead_assignment_remover: public traversing_visitor
   // called with null current_expr.
 
   void visit_assignment (assignment* e);
+
+  void visit_arrayindex (arrayindex* e);
 };
 
 
@@ -1714,6 +1716,8 @@ dead_assignment_remover::visit_assignment (assignment* e)
       *current_expr == e && // we're not nested any deeper than expected 
       leftvar) // not unresolved $target; intended sideeffect cannot be elided
     {
+      e->left->visit (this);
+      e->right->visit (this);
       if (vut.read.find(leftvar) == vut.read.end()) // var never read?
         {
           // NB: Not so fast!  The left side could be an array whose
@@ -1744,6 +1748,24 @@ dead_assignment_remover::visit_assignment (assignment* e)
     }
 }
 
+void
+dead_assignment_remover::visit_arrayindex (arrayindex *e)
+{
+  symbol *array = NULL;
+  hist_op *hist = NULL;
+  classify_indexable(e->base, array, hist);
+
+  if (array)
+    {
+      expression** last_expr = current_expr;
+      for (unsigned i=0; i < e->indexes.size(); i++)
+	{
+	  current_expr = & e->indexes[i];
+	  e->indexes[i]->visit (this);
+	}
+      current_expr = last_expr;
+    }
+}
 
 // Let's remove assignments to variables that are never read.  We
 // rewrite "(foo = expr)" as "(expr)".  This makes foo a candidate to
diff --git a/testsuite/systemtap.base/optim_arridx.exp b/testsuite/systemtap.base/optim_arridx.exp
new file mode 100644
index 0000000..8480f39
--- /dev/null
+++ b/testsuite/systemtap.base/optim_arridx.exp
@@ -0,0 +1,50 @@
+# test integer limits. Set and print variables and print constants.
+
+set test "optim_arridx"
+set ::result_string {# globals
+arr1:long [long, long]
+arr2:long [long]
+arr3:long [long]
+# functions
+fna:long (a:long)
+fnb:long (a:long, b:long)
+exit:unknown ()
+# probes
+begin /* <- begin */
+  # locals
+  idx2:long
+  j:long
+  k:long
+  b:long
+  m:long
+  arr1:long [long]
+  arr2:long [long, long]
+WARNING: eliding unused variable identifier 'elide_i'.*
+WARNING: eliding unused variable identifier 'elide_c'.*
+WARNING: eliding unused variable identifier 'elide_n'.*
+WARNING: eliding unused variable identifier 'elide_idx1'.*
+}
+
+proc optim_arridx_run { TEST_NAME args } {
+    # zap the srcdir prefix
+    set test_file_name $TEST_NAME
+    set TEST_NAME [regsub {.*/testsuite/} $TEST_NAME ""]
+    
+    set cmd [concat stap $args $test_file_name]
+    catch {eval exec $cmd} res
+
+    set n 0
+    set expected [split $::result_string "\n"]
+    foreach line [split $res "\n"] {
+	if {![string equal $line [lindex $expected $n]]} {
+	    fail "$TEST_NAME"
+	    send_log "line [expr $n + 1]: expected \"[lindex $expected $n]\"\n"
+	    send_log "Got \"$line\"\n"
+	    return
+	}
+	incr n
+    }
+    pass "$TEST_NAME"
+}
+
+optim_arridx_run $srcdir/$subdir/$test.stp -p2 2>/dev/null
diff --git a/testsuite/systemtap.base/optim_arridx.stp b/testsuite/systemtap.base/optim_arridx.stp
new file mode 100644
index 0000000..f6ec96c
--- /dev/null
+++ b/testsuite/systemtap.base/optim_arridx.stp
@@ -0,0 +1,21 @@
+global arr1, arr2, arr3, elide_idx1
+
+function fna(a:long) {return a}
+function fnb(a:long, b:long) {return a+b}
+
+probe begin {
+  arr2[elide_idx1 = 1] = 10
+  arr2[idx2 = 2] = 20
+  arr2[elide_i=3] = 30
+  arr2[j=4] = 40
+  arr1[fna(k = 0), k] = 1
+  arr1[b = 1, b] = 2
+  arr1[elide_c = 2,2] = 3
+  fnb(arr3[0] = 4, arr3[0])
+  m = 1
+  for (elide_n=2; m <= 10; m++)
+    arr2[m] = m * 10
+  printf ("%d %d %d %d\n", arr1[0], arr2[0,0], idx2, j)
+  
+  exit ()
+}