Prevent -Og from deleting stores to write-only variables

This patch prevents -Og from deleting stores to write-only variables,
so that the values are still available when debugging.  This seems
more convenient than forcing users to use __attribute__((used))
(probably conditionally, if it's not something they want in release
builds).

2019-07-29  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-cfg.c (execute_fixup_cfg): Don't delete stores to write-only
	variables for -Og.

gcc/testsuite/
	* c-c++-common/guality/Og-static-wo-1.c: New test.
	* g++.dg/guality/guality.exp: Separate the c-c++-common tests into
	"Og" and "general" tests.  Run the latter at -O0 and -Og only.
	* gcc.dg/guality/guality.exp: Likewise.

From-SVN: r273870

gcc/ChangeLog

 2019-07-29  Richard Sandiford  <richard.sandiford@arm.com>
 
+	* tree-cfg.c (execute_fixup_cfg): Don't delete stores to write-only
+	variables for -Og.
+
+2019-07-29  Richard Sandiford  <richard.sandiford@arm.com>
+
 	* doc/sourcebuild.texi (check-function-bodies): Document.
 
 2019-07-29  Richard Sandiford  <richard.sandiford@arm.com>

gcc/testsuite/ChangeLog

 2019-07-29  Richard Sandiford  <richard.sandiford@arm.com>
 
+	* c-c++-common/guality/Og-static-wo-1.c: New test.
+	* g++.dg/guality/guality.exp: Separate the c-c++-common tests into
+	"Og" and "general" tests.  Run the latter at -O0 and -Og only.
+	* gcc.dg/guality/guality.exp: Likewise.
+
+2019-07-29  Richard Sandiford  <richard.sandiford@arm.com>
+
 	* lib/scanasm.exp (parse_function_bodies, check_function_body)
 	(check-function-bodies): New procedures.
 	* gcc.target/aarch64/sve/init_1.c: Use check-function-bodies

gcc/testsuite/c-c++-common/guality/Og-static-wo-1.c

+/* { dg-do run } */
+/* { dg-options "-g" } */
+
+#include "../../gcc.dg/nop.h"
+
+static int x = 0;
+
+int
+main (void)
+{
+  asm volatile (NOP);		/* { dg-final { gdb-test . "x" "0" } } */
+  x = 1;
+  asm volatile (NOP);		/* { dg-final { gdb-test . "x" "1" } } */
+  return 0;
+}

gcc/testsuite/g++.dg/guality/guality.exp

@@ -65,8 +65,22 @@ if {[check_guality "
     return 0;
   }
 "]} {
-  gcc-dg-runtest [lsort [glob $srcdir/$subdir/*.C]] "" ""
-  gcc-dg-runtest [lsort [glob $srcdir/c-c++-common/guality/*.c]] "" ""
+    set general [list]
+    set Og [list]
+    foreach file [lsort [glob $srcdir/c-c++-common/guality/*.c]] {
+	switch -glob -- [file tail $file] {
+	    Og-* { lappend Og $file }
+	    * { lappend general $file }
+	}
+    }
+
+    gcc-dg-runtest [lsort [glob $srcdir/$subdir/*.C]] "" ""
+    gcc-dg-runtest $general "" ""
+    set-torture-options \
+	[list "-O0" "-Og"] \
+	[list {}] \
+	[list "-Og -flto"]
+    gcc-dg-runtest $Og "" ""
 }
 
 if [info exists guality_gdb_name] {

gcc/testsuite/gcc.dg/guality/guality.exp

@@ -80,8 +80,22 @@ if {[check_guality "
     return 0;
   }
 "]} {
-  gcc-dg-runtest [lsort [glob $srcdir/$subdir/*.c]] "" ""
-  gcc-dg-runtest [lsort [glob $srcdir/c-c++-common/guality/*.c]] "" "-Wc++-compat"
+    set general [list]
+    set Og [list]
+    foreach file [lsort [glob $srcdir/c-c++-common/guality/*.c]] {
+	switch -glob -- [file tail $file] {
+	    Og-* { lappend Og $file }
+	    * { lappend general $file }
+	}
+    }
+
+    gcc-dg-runtest [lsort [glob $srcdir/$subdir/*.c]] "" ""
+    gcc-dg-runtest $general "" "-Wc++-compat"
+    set-torture-options \
+	[list "-O0" "-Og"] \
+	[list {}] \
+	[list "-Og -flto"]
+    gcc-dg-runtest $Og "" "-Wc++-compat"
 }
 
 if [info exists guality_gdb_name] {

gcc/tree-cfg.c

@@ -9579,7 +9579,8 @@ execute_fixup_cfg (void)
 	     Keep access when store has side effect, i.e. in case when source
 	     is volatile.  */
 	  if (gimple_store_p (stmt)
-	      && !gimple_has_side_effects (stmt))
+	      && !gimple_has_side_effects (stmt)
+	      && !optimize_debug)
 	    {
 	      tree lhs = get_base_address (gimple_get_lhs (stmt));