avr: Fix wrong array bounds warning on SFR access

The warning was raised on accessing SFRs at addresses below the default
page size, as gcc considers accessing addresses in the first page of
memory as suspicious. This doesn't apply to an embedded target like the
avr, where both flash and RAM have zero as a valid address. Zero is also
a valid address in named address spaces (__memx, flash<n> etc..).

This commit implements TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID for the avr
target and reports to gcc that zero is a valid address on all
address spaces. It also disables flag_delete_null_pointer_checks
based on the target hook, and modifies target-supports.exp to add avr
to the list of targets that always keep null pointer checks. This fixes
a bunch of DejaGNU failures that occur otherwise.

	PR target/105523

gcc/ChangeLog:

	* common/config/avr/avr-common.cc: Remove setting
	of OPT_fdelete_null_pointer_checks.
	* config/avr/avr.cc (avr_option_override): Clear
	flag_delete_null_pointer_checks if zero_address_valid.
	(avr_addr_space_zero_address_valid): New function.
	(TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID): Provide target
	hook.

gcc/testsuite/ChangeLog:

	* lib/target-supports.exp
	(check_effective_target_keeps_null_pointer_checks): Add
	avr.
	* gcc.target/avr/pr105523.c: New test.

(cherry picked from commit 58e1bc2b1c8420773b16452d47932a6ca0d003fb)

diff --git a/gcc/common/config/avr/avr-common.cc b/gcc/common/config/avr/avr-common.cc
index 2ad02448e290c710137d6605e08a90ed8642a9a7..2f874c5b81c7c822f3cb7a8c246905107577a518 100644 (file)
--- a/gcc/common/config/avr/avr-common.cc
+++ b/gcc/common/config/avr/avr-common.cc
@@ -29,12 +29,6 @@
 /* Implement TARGET_OPTION_OPTIMIZATION_TABLE.  */
 static const struct default_options avr_option_optimization_table[] =
   {
-    // With -fdelete-null-pointer-checks option, the compiler assumes
-    // that dereferencing of a null pointer would halt the program.
-    // For AVR this assumption is not true and a program can safely
-    // dereference null pointers.  Changes made by this option may not
-    // work properly for AVR.  So disable this option.
-    { OPT_LEVELS_ALL, OPT_fdelete_null_pointer_checks, NULL, 0 },
     // The only effect of -fcaller-saves might be that it triggers
     // a frame without need when it tries to be smart around calls.
     { OPT_LEVELS_ALL, OPT_fcaller_saves, NULL, 0 },

diff --git a/gcc/config/avr/avr.cc b/gcc/config/avr/avr.cc
index b50fe3b6bf5331d2b768079d33b35337fb18d745..0f046eba26dcae169071115d8e9f75cd5d0c2df3 100644 (file)
--- a/gcc/config/avr/avr.cc
+++ b/gcc/config/avr/avr.cc
@@ -1097,6 +1097,10 @@ avr_option_override (void)
       flag_omit_frame_pointer = 0;
     }
 
+  /* Disable flag_delete_null_pointer_checks if zero is a valid address. */
+  if (targetm.addr_space.zero_address_valid (ADDR_SPACE_GENERIC))
+    flag_delete_null_pointer_checks = 0;
+
   if (flag_pic == 1)
     warning (OPT_fpic, "%<-fpic%> is not supported");
   if (flag_pic == 2)
@@ -10387,6 +10391,16 @@ avr_addr_space_diagnose_usage (addr_space_t as, location_t loc)
   (void) avr_addr_space_supported_p (as, loc);
 }
 
+/* Implement `TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID. Zero is a valid
+   address in all address spaces. Even in ADDR_SPACE_FLASH1 etc..,
+   a zero address is valid and means 0x<RAMPZ val>0000, where RAMPZ is
+   set to the appropriate segment value. */
+
+static bool
+avr_addr_space_zero_address_valid (addr_space_t)
+{
+  return true;
+}
 
 /* Look if DECL shall be placed in program memory space by
    means of attribute `progmem' or some address-space qualifier.
@@ -15197,6 +15211,9 @@ avr_float_lib_compare_returns_bool (machine_mode mode, enum rtx_code)
 #undef  TARGET_ADDR_SPACE_DIAGNOSE_USAGE
 #define TARGET_ADDR_SPACE_DIAGNOSE_USAGE avr_addr_space_diagnose_usage
 
+#undef  TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID
+#define TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID avr_addr_space_zero_address_valid
+
 #undef  TARGET_MODE_DEPENDENT_ADDRESS_P
 #define TARGET_MODE_DEPENDENT_ADDRESS_P avr_mode_dependent_address_p
 

diff --git a/gcc/testsuite/gcc.target/avr/pr105523.c b/gcc/testsuite/gcc.target/avr/pr105523.c
new file mode 100644 (file)
index 0000000..fbbf7bf
--- /dev/null
+++ b/gcc/testsuite/gcc.target/avr/pr105523.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-Os -Wall" } */
+
+/* Verify no "array subscript 0 is outside array bounds of" is generated
+   for accessing memory addresses in the 0-4096 range. */
+
+typedef __UINT8_TYPE__ uint8_t;
+
+#define SREG (*(volatile uint8_t*) (0x3F + __AVR_SFR_OFFSET__ ))
+
+void bar (void)
+{
+    SREG = 0;
+}

diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 4d6bf2eb8d32d562d61962e2fed5d448760fefa7..9e189d91e4b0389f1a99e228c8dedb284911831b 100644 (file)
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -686,7 +686,8 @@ proc check_effective_target_keeps_null_pointer_checks { } {
     if [target_info exists keeps_null_pointer_checks] {
       return 1
     }
-    if { [istarget msp430-*-*] } {
+    if { [istarget msp430-*-*]
+         || [istarget avr-*-*] } {
        return 1;   
     }
     return 0