[rfc, stage 1] default to -fno-delete-null-pointer-checks on nios2-elf

[rfc, stage 1] default to -fno-delete-null-pointer-checks on nios2-elf

[Sandra Loosemore]

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As the outcome of this discussion last month about unexpected behavior 
of -fisolate-erroneous-paths-dereference

https://gcc.gnu.org/ml/gcc/2015-02/msg00163.html

Altera has asked us to turn off -fdelete-null-pointer-checks on 
nios2-elf targets.  Presently, the AVR and CR16 back ends completely 
disable this option, but it seems to me that a better solution is to 
simply default it to off.  That's what the attached patch does for 
nios2, with appropriate adjustments to the testsuite.

The rationale for defaulting to -fno-delete-null-pointer-checks on a 
bare-metal target is that it is the "safe" setting on targets where 0 is 
a valid memory address, and where the hardware may even require 
placement of e.g. a reset vector at that address.  Also, library code 
should be built to be "safe", especially things like memcpy that might 
be used by implicit compiler-generated calls.

The rationale for allowing the default to be overridden on the command 
line, instead of disabling -fdelete-null-pointer-checks entirely, is 
that it's much more common for programs *not* to manipulate code or data 
at address 0, and we can generate smaller/faster code by enabling the 
option.

So....

(1) Is the change to the default for this flag in common.opt OK?  I 
verified that all existing uses just check for zero/non-zero-ness.

(2) If the AVR and CR16 maintainers agree that defaulting the option to 
off rather than being completely disabling it is a better solution for 
their targets, too, I think being consistent across the three targets 
would simplify ongoing support -- e.g., the testsuite bits could be 
greatly simplified by getting rid of 
check_effective_target_keeps_null_pointer_checks and checks for 
keeps_null_pointer_checks entirely.  WDYT?

I haven't done a full bootstrap with this patch yet....  I'd just like 
to get it out there for discussion to see if there is consensus that 
this is a reasonable approach, first.  This is stage 1 material in any case.

-Sandra


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2015-03-29  Sandra Loosemore  <sandra@codesourcery.com>

	gcc/
	* common.opt (fdelete-null-pointer-checks): Init to -1.
	* config/nios2/elf.h (SUBTARGET_OVERRIDE_OPTIONS): Define to
	override flag_delete_null_pointer_checks default.
	* doc/invoke.texi (-fdelete-null-pointer-checks): Clarify
	behavior re address zero.  Better document target-specific behavior.
	(-fisolate-errneous-paths-dereference): Mention relationship to
	-fdelete-null-pointer-checks.

	gcc/testsuite/
	* lib/target-supports.exp
	(check_effective_target_keeps_null_pointer_checks): Clarify that
	this is for targets that disable -fdelete-null-pointer-checks,
	not default it to off.
	* gcc.dg/ipa/ipa-pta-14.c: Make dependence on
	-fdelete-null-pointer-checks explicit.
	* gcc.dg/tree-ssa/20030730-1.c: Likewise.
	* gcc.dg/tree-ssa/20030730-2.c: Likewise.
	* gcc.dg/tree-ssa/isolate-1.c: Likewise.
	* gcc.dg/tree-ssa/isolate-2.c: Likewise.
	* gcc.dg/tree-ssa/isolate-3.c: Likewise.
	* gcc.dg/tree-ssa/isolate-4.c: Likewise.
	* gcc.dg/tree-ssa/isolate-5.c: Likewise.
	* gcc.dg/tree-ssa/nonzero-1.c: Likewise.
	* gcc.dg/tree-ssa/pr20318.c: Likewise.
	* gcc.dg/tree-ssa/pr20701.c: Likewise.
	* gcc.dg/tree-ssa/pr20702.c: Likewise.
	* gcc.dg/tree-ssa/pr21086.c: Likewise.
	* gcc.dg/tree-ssa/pr21090.c: Likewise.
	* gcc.dg/tree-ssa/pr58480.c: Likewise.
	* gcc.dg/tree-ssa/pta-escape-1.c: Likewise.
	* gcc.dg/tree-ssa/pta-escape-2.c: Likewise.
	* gcc.dg/tree-ssa/pta-escape-3.c: Likewise.
	* gcc.dg/tree-ssa/ssa-vrp-thread-1.c: Likewise.
	* gcc.dg/tree-ssa/unreachable.c: Likewise.
	* gcc.dg/tree-ssa/vrp02.c: Likewise.
	* gcc.dg/tree-ssa/vrp07.c: Likewise.
	* gcc.dg/tree-ssa/vrp08.c: Likewise.
	* gcc.dg/tree-ssa/vrp55.c: Likewise.
	* g++.dg/cpp0x/static_assert9.C: Likewise.
	* g++.dg/tree-ssa/nonzero-1.C: Likewise.
	* g++.dg/tree-ssa/pr19476-1.C: Likewise.
	* g++.dg/tree-ssa/pr19476-2.C: Likewise.
	* g++.dg/tree-ssa/pr19476-5.C: Likewise.
	* g++.dg/tree-ssa/pr26406.C: Likewise.

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Index: gcc/common.opt
===================================================================
--- gcc/common.opt	(revision 221677)
+++ gcc/common.opt	(working copy)
@@ -1065,7 +1065,7 @@ Common Report Var(flag_delete_dead_excep
 Delete dead instructions that may throw exceptions
 
 fdelete-null-pointer-checks
-Common Report Var(flag_delete_null_pointer_checks) Init(1) Optimization
+Common Report Var(flag_delete_null_pointer_checks) Init(-1) Optimization
 Delete useless null pointer checks
 
 fdevirtualize-at-ltrans
Index: gcc/config/nios2/elf.h
===================================================================
--- gcc/config/nios2/elf.h	(revision 221677)
+++ gcc/config/nios2/elf.h	(working copy)
@@ -50,3 +50,12 @@
 /* The ELF target doesn't support the Nios II Linux ABI.  */
 #define TARGET_LINUX_ABI 0
 
+/* Default -fdelete-null-pointer-checks to off, to prevent the compiler
+   from treating accesses to address zero as traps.  On bare-metal Nios II
+   targets address zero may legitimately be mapped to memory (e.g., the
+   hardware description may specify this as the address of the interrupt
+   vector).  Users can override this on the command line to get the
+   additional optimizations it enables.  */
+#define SUBTARGET_OVERRIDE_OPTIONS 		\
+  if (flag_delete_null_pointer_checks < 0)	\
+    flag_delete_null_pointer_checks = 0
Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi	(revision 221677)
+++ gcc/doc/invoke.texi	(working copy)
@@ -7993,10 +7993,12 @@ Enabled by @option{-Os}.
 @item -fdelete-null-pointer-checks
 @opindex fdelete-null-pointer-checks
 Assume that programs cannot safely dereference null pointers, and that
-no code or data element resides there.  This enables simple constant
+no code or data element resides at address zero.
+This option enables simple constant
 folding optimizations at all optimization levels.  In addition, other
 optimization passes in GCC use this flag to control global dataflow
 analyses that eliminate useless checks for null pointers; these assume
+that a memory access to address zero always results in a trap, so
 that if a pointer is checked after it has already been dereferenced,
 it cannot be null.
 
@@ -8004,9 +8006,10 @@ Note however that in some environments t
 Use @option{-fno-delete-null-pointer-checks} to disable this optimization
 for programs that depend on that behavior.
 
-Some targets, especially embedded ones, disable this option at all levels.
-Otherwise it is enabled at all levels: @option{-O0}, @option{-O1},
-@option{-O2}, @option{-O3}, @option{-Os}.  Passes that use the information
+This option is enabled by default on most targets.  On Nios II ELF, it
+defaults to off.  On AVR and CR16, this option is completely disabled.  
+
+Passes that use the dataflow information
 are enabled independently at different optimization levels.
 
 @item -fdevirtualize
@@ -8489,7 +8492,8 @@ This flag is enabled by default at @opti
 Detect paths that trigger erroneous or undefined behavior due to
 dereferencing a null pointer.  Isolate those paths from the main control
 flow and turn the statement with erroneous or undefined behavior into a trap.
-This flag is enabled by default at @option{-O2} and higher.
+This flag is enabled by default at @option{-O2} and higher and depends on
+@option{-fdelete-null-pointer-checks} also being enabled.
 
 @item -fisolate-erroneous-paths-attribute
 @opindex fisolate-erroneous-paths-attribute
Index: gcc/testsuite/lib/target-supports.exp
===================================================================
--- gcc/testsuite/lib/target-supports.exp	(revision 221677)
+++ gcc/testsuite/lib/target-supports.exp	(working copy)
@@ -458,9 +458,11 @@ proc check_effective_target_trampolines 
 }
 
 # Return 1 if according to target_info struct and explicit target list
-# target is supposed to keep null pointer checks. This could be due to 
-# use of option fno-delete-null-pointer-checks or hardwired in target.
- 
+# target disables -fdelete-null-pointer-checks.  Targets should return 0
+# if they simply default to -fno-delete-null-pointer-checks but obey
+# -fdelete-null-pointer-checks when passed explicitly (and tests that 
+# depend on this option should do that).
+
 proc check_effective_target_keeps_null_pointer_checks { } {
     if [target_info exists keeps_null_pointer_checks] {
       return 1
Index: gcc/testsuite/gcc.dg/ipa/ipa-pta-14.c
===================================================================
--- gcc/testsuite/gcc.dg/ipa/ipa-pta-14.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/ipa/ipa-pta-14.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do run } */
-/* { dg-options "-O2 -fipa-pta -fno-tree-fre -fno-tree-sra -fdump-ipa-pta-details" } */
+/* { dg-options "-O2 -fipa-pta -fno-tree-fre -fno-tree-sra -fdump-ipa-pta-details -fdelete-null-pointer-checks" } */
 
 struct X {
     int i;
Index: gcc/testsuite/gcc.dg/tree-ssa/20030730-1.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/20030730-1.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/20030730-1.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-dom2" } */
+/* { dg-options "-O2 -fdump-tree-dom2 -fdelete-null-pointer-checks" } */
      
 extern void exit (int);
 extern void *ggc_alloc (__SIZE_TYPE__);
@@ -18,7 +18,7 @@ foo (int attr_kind, unsigned long offset
     exit (0);
 }
 
-/* There should be no IF conditionals, unless target has fno-delete-null-pointer-checks  */
+/* There should be no IF conditionals, unless target disables -fdelete-null-pointer-checks  */
 /* { dg-final { scan-tree-dump-times "if " 0 "dom2" { target { ! keeps_null_pointer_checks } } } } */
 /* { dg-final { scan-tree-dump "if " "dom2" { target { keeps_null_pointer_checks } } } } */
      
Index: gcc/testsuite/gcc.dg/tree-ssa/20030730-2.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/20030730-2.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/20030730-2.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-dom2" } */
+/* { dg-options "-O2 -fdump-tree-dom2 -fdelete-null-pointer-checks" } */
      
 extern void exit (int);
 extern void *ggc_alloc (__SIZE_TYPE__);
@@ -18,7 +18,7 @@ foo (int attr_kind, unsigned long offset
     exit (0);
 }
 
-/* There should be no IF conditionals, unless target has fno-delete-null-pointer-checks  */
+/* There should be no IF conditionals, unless target disables -fdelete-null-pointer-checks  */
 /* { dg-final { scan-tree-dump-times "if " 0 "dom2" { target { ! keeps_null_pointer_checks } } } } */
 /* { dg-final { scan-tree-dump "if " "dom2" { target { keeps_null_pointer_checks } } } } */
 
Index: gcc/testsuite/gcc.dg/tree-ssa/isolate-1.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/isolate-1.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/isolate-1.c	(working copy)
@@ -1,6 +1,6 @@
 
 /* { dg-do compile } */ 
-/* { dg-options "-O2 -fdump-tree-isolate-paths" } */
+/* { dg-options "-O2 -fdump-tree-isolate-paths -fdelete-null-pointer-checks" } */
 /* { dg-skip-if "" keeps_null_pointer_checks } */
 
 
Index: gcc/testsuite/gcc.dg/tree-ssa/isolate-2.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/isolate-2.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/isolate-2.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */ 
-/* { dg-options "-O2 -fisolate-erroneous-paths-attribute -fdump-tree-isolate-paths -fdump-tree-phicprop1" } */
+/* { dg-options "-O2 -fdelete-null-pointer-checks -fisolate-erroneous-paths-attribute -fdump-tree-isolate-paths -fdump-tree-phicprop1" } */
 /* { dg-skip-if "" keeps_null_pointer_checks } */
 
 
Index: gcc/testsuite/gcc.dg/tree-ssa/isolate-3.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/isolate-3.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/isolate-3.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */ 
-/* { dg-options "-O2 -fdump-tree-isolate-paths" } */
+/* { dg-options "-O2 -fdump-tree-isolate-paths -fdelete-null-pointer-checks" } */
 /* { dg-skip-if "" keeps_null_pointer_checks } */
 
 
Index: gcc/testsuite/gcc.dg/tree-ssa/isolate-4.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/isolate-4.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/isolate-4.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */ 
-/* { dg-options "-O2 -fisolate-erroneous-paths-attribute -fdump-tree-isolate-paths -fdump-tree-phicprop1" } */
+/* { dg-options "-O2 -fdelete-null-pointer-checks -fisolate-erroneous-paths-attribute -fdump-tree-isolate-paths -fdump-tree-phicprop1" } */
 /* { dg-skip-if "" keeps_null_pointer_checks } */
 
 
Index: gcc/testsuite/gcc.dg/tree-ssa/isolate-5.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/isolate-5.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/isolate-5.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */ 
-/* { dg-options "-O2 -fdump-tree-isolate-paths -fdump-tree-optimized" } */
+/* { dg-options "-O2 -fdelete-null-pointer-checks -fdump-tree-isolate-paths -fdump-tree-optimized" } */
 /* { dg-skip-if "" keeps_null_pointer_checks } */
 
 struct demangle_component
Index: gcc/testsuite/gcc.dg/tree-ssa/nonzero-1.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/nonzero-1.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/nonzero-1.c	(working copy)
@@ -1,5 +1,7 @@
 /* { dg-do compile } */
-/* { dg-options "-O2" } */
+/* { dg-options "-O2 -fdelete-null-pointer-checks" } */
+
+/* { dg-skip-if "" keeps_null_pointer_checks } */
 extern int a; /* { dg-error "declared weak after being used" } */
 int
 t()
Index: gcc/testsuite/gcc.dg/tree-ssa/pr20318.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr20318.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr20318.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile { target { ! keeps_null_pointer_checks } } } */
-/* { dg-options "-O2 -fdump-tree-original -fdump-tree-vrp1" } */
+/* { dg-options "-O2 -fdump-tree-original -fdump-tree-vrp1 -fdelete-null-pointer-checks" } */
 
 extern int* f(int) __attribute__((returns_nonnull));
 extern void eliminate ();
Index: gcc/testsuite/gcc.dg/tree-ssa/pr20701.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr20701.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr20701.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1 -fno-early-inlining" } */
+/* { dg-options "-O2 -fdump-tree-vrp1 -fno-early-inlining -fdelete-null-pointer-checks" } */
 
 typedef struct {
   int code;
@@ -35,7 +35,7 @@ can_combine_p (rtx insn, rtx elt)
   return 0;
 }
 
-/* Target with fno-delete-null-pointer-checks should not fold checks */
+/* Target disabling -fdelete-null-pointer-checks should not fold checks */
 /* { dg-final { scan-tree-dump-times "Folding predicate.*to 0" 1 "vrp1" { target { ! keeps_null_pointer_checks } } } } */
 /* { dg-final { scan-tree-dump-times "Folding predicate.*to 0" 0 "vrp1" { target {   keeps_null_pointer_checks } } } } */
 /* { dg-final { cleanup-tree-dump "vrp1" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/pr20702.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr20702.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr20702.c	(working copy)
@@ -4,7 +4,7 @@
    immediate successors of the basic block.  */
 
 /* { dg-do compile } */
-/* { dg-options "-O2 -fno-tree-dominator-opts -fdump-tree-vrp1-details" } */
+/* { dg-options "-O2 -fno-tree-dominator-opts -fdump-tree-vrp1-details -fdelete-null-pointer-checks" } */
 
 extern void bar (int);
 
@@ -25,7 +25,7 @@ foo (int *p, int b)
   return a;
 }
 
-/* Target with fno-delete-null-pointer-checks should not fold checks */
+/* Target disabling -fdelete-null-pointer-checks should not fold checks */
 /* { dg-final { scan-tree-dump-times "Folding predicate" 1 "vrp1" { target { ! keeps_null_pointer_checks } } } } */
 /* { dg-final { scan-tree-dump-times "Folding predicate" 0 "vrp1" { target {   keeps_null_pointer_checks } } } } */
 /* { dg-final { cleanup-tree-dump "vrp1" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/pr21086.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr21086.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr21086.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1 -fdump-tree-dce1" } */
+/* { dg-options "-O2 -fdump-tree-vrp1 -fdump-tree-dce1 -fdelete-null-pointer-checks" } */
 
 int
 foo (int *p)
@@ -15,7 +15,7 @@ foo (int *p)
     return 0;
 }
 
-/* Target with fno-delete-null-pointer-checks should not fold checks */
+/* Target disabling -fdelete-null-pointer-checks should not fold checks */
 /* { dg-final { scan-tree-dump "Folding predicate " "vrp1" { target { ! keeps_null_pointer_checks } } } } */
 /* { dg-final { scan-tree-dump-times "Folding predicate " 0 "vrp1" { target {   keeps_null_pointer_checks } } } } */
 /* { dg-final { scan-tree-dump-not "b_. =" "dce1" { target { ! avr-*-* } } } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/pr21090.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr21090.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr21090.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1" } */
+/* { dg-options "-O2 -fdump-tree-vrp1 -fdelete-null-pointer-checks" } */
 
 int g, h;
 
Index: gcc/testsuite/gcc.dg/tree-ssa/pr58480.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr58480.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr58480.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile { target { ! keeps_null_pointer_checks } } } */
-/* { dg-options "-O2 -fdump-tree-vrp1" } */
+/* { dg-options "-O2 -fdump-tree-vrp1 -fdelete-null-pointer-checks" } */
 
 extern void eliminate (void);
 extern void* f1 (void *a, void *b) __attribute__((nonnull));
Index: gcc/testsuite/gcc.dg/tree-ssa/pta-escape-1.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pta-escape-1.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/pta-escape-1.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do run } */
-/* { dg-options "-O -fdump-tree-alias-details" } */
+/* { dg-options "-O -fdump-tree-alias-details -fdelete-null-pointer-checks" } */
 
 int *i;
 void __attribute__((noinline))
Index: gcc/testsuite/gcc.dg/tree-ssa/pta-escape-2.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pta-escape-2.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/pta-escape-2.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do run } */
-/* { dg-options "-O -fdump-tree-alias-details" } */
+/* { dg-options "-O -fdump-tree-alias-details -fdelete-null-pointer-checks" } */
 
 int *i;
 void __attribute__((noinline))
Index: gcc/testsuite/gcc.dg/tree-ssa/pta-escape-3.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pta-escape-3.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/pta-escape-3.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do run } */
-/* { dg-options "-O -fdump-tree-alias-details" } */
+/* { dg-options "-O -fdump-tree-alias-details -fdelete-null-pointer-checks" } */
 
 int *i;
 void __attribute__((noinline))
Index: gcc/testsuite/gcc.dg/tree-ssa/ssa-vrp-thread-1.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/ssa-vrp-thread-1.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/ssa-vrp-thread-1.c	(working copy)
@@ -1,5 +1,6 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1-details" } */
+/* { dg-options "-O2 -fdump-tree-vrp1-details -fdelete-null-pointer-checks" } */
+/* { dg-skip-if "" keeps_null_pointer_checks } */
 
 void oof (void);
 struct basic_block_def;
Index: gcc/testsuite/gcc.dg/tree-ssa/unreachable.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/unreachable.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/unreachable.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O1 -fdump-tree-optimized" } */
+/* { dg-options "-O1 -fdump-tree-optimized -fdelete-null-pointer-checks" } */
 static void bad_boy()
 {
 }
Index: gcc/testsuite/gcc.dg/tree-ssa/vrp02.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/vrp02.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/vrp02.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1" } */
+/* { dg-options "-O2 -fdump-tree-vrp1 -fdelete-null-pointer-checks" } */
 
 struct A
 {
@@ -20,7 +20,7 @@ foo (struct A *p, struct A *q)
   if (p)
     return x + p->b;
 }
-/* Target with fno-delete-null-pointer-checks should not fold check */
+/* Target disabling -fdelete-null-pointer-checks should not fold check */
 /* { dg-final { scan-tree-dump-times "Folding predicate p_.*to 1" 1 "vrp1" { target { ! keeps_null_pointer_checks } } } } */
 /* { dg-final { scan-tree-dump-times "Folding predicate p_.*to 1" 0 "vrp1" { target {   keeps_null_pointer_checks } } } } */
 /* { dg-final { cleanup-tree-dump "vrp1" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/vrp07.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/vrp07.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/vrp07.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1-details" } */
+/* { dg-options "-O2 -fdump-tree-vrp1-details -fdelete-null-pointer-checks" } */
 
 int
 foo (int i, int *p)
@@ -30,7 +30,7 @@ foo (int i, int *p)
 
   return i;
 }
-/* Target with fno-delete-null-pointer-checks should not fold checks */
+/* Target disabling -fdelete-null-pointer-checks should not fold checks */
 /* { dg-final { scan-tree-dump-times "Folding predicate p_.*to 1" 1 "vrp1" } } */
 /* { dg-final { scan-tree-dump-times "Folding predicate p_.*to 0" 1 "vrp1" { target { ! keeps_null_pointer_checks } } } } */
 /* { dg-final { scan-tree-dump-times "Folding predicate p_.*to 0" 0 "vrp1" { target {   keeps_null_pointer_checks } } } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/vrp08.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/vrp08.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/vrp08.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fno-tree-fre -fdump-tree-vrp1-details" } */
+/* { dg-options "-O2 -fno-tree-fre -fdump-tree-vrp1-details -fdelete-null-pointer-checks" } */
 
 /* Compile with -fno-tree-fre -O2 to prevent CSEing *p.  */
 int
@@ -18,7 +18,7 @@ foo (int a, int *p)
 
   return a;
 }
-/* Target with fno-delete-null-pointer-checks should not fold checks */
+/* Target disabling -fdelete-null-pointer-checks should not fold checks */
 /* { dg-final { scan-tree-dump-times "Folding predicate p_.*to 1" 1 "vrp1" { target { ! keeps_null_pointer_checks } } } } */
 /* { dg-final { scan-tree-dump-times "PREDICATE: p_.* ne_expr 0" 1 "vrp1" { target { ! keeps_null_pointer_checks } } } } */
 /* { dg-final { scan-tree-dump-times "Folding predicate p_.*to 1" 0 "vrp1" { target {   keeps_null_pointer_checks } } } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/vrp55.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/vrp55.c	(revision 221677)
+++ gcc/testsuite/gcc.dg/tree-ssa/vrp55.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-vrp1-blocks-vops-details" } */
+/* { dg-options "-O2 -fdump-tree-vrp1-blocks-vops-details -fdelete-null-pointer-checks" } */
 
 void arf (void);
 
Index: gcc/testsuite/g++.dg/cpp0x/static_assert9.C
===================================================================
--- gcc/testsuite/g++.dg/cpp0x/static_assert9.C	(revision 221677)
+++ gcc/testsuite/g++.dg/cpp0x/static_assert9.C	(working copy)
@@ -1,5 +1,7 @@
 // PR c++/58837
 // { dg-require-effective-target c++11 }
+// { dg-skip-if "" keeps_null_pointer_checks }
+// { dg-options "-fdelete-null-pointer-checks" }
 
 void f();
 static_assert(f, "");
Index: gcc/testsuite/g++.dg/tree-ssa/nonzero-1.C
===================================================================
--- gcc/testsuite/g++.dg/tree-ssa/nonzero-1.C	(revision 221677)
+++ gcc/testsuite/g++.dg/tree-ssa/nonzero-1.C	(working copy)
@@ -1,5 +1,7 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-ccp1" } */
+/* { dg-options "-O2 -fdump-tree-ccp1 -fdelete-null-pointer-checks" } */
+/* { dg-skip-if "" keeps_null_pointer_checks } */
+
 inline void t()
 {
 }
Index: gcc/testsuite/g++.dg/tree-ssa/pr19476-1.C
===================================================================
--- gcc/testsuite/g++.dg/tree-ssa/pr19476-1.C	(revision 221677)
+++ gcc/testsuite/g++.dg/tree-ssa/pr19476-1.C	(working copy)
@@ -1,5 +1,6 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fdump-tree-ccp1" } */
+/* { dg-options "-O -fdump-tree-ccp1 -fdelete-null-pointer-checks" } */
+/* { dg-skip-if "" keeps_null_pointer_checks } */
 
 // See pr19476-5.C for a version without including <new>.
 #include <new>
Index: gcc/testsuite/g++.dg/tree-ssa/pr19476-2.C
===================================================================
--- gcc/testsuite/g++.dg/tree-ssa/pr19476-2.C	(revision 221677)
+++ gcc/testsuite/g++.dg/tree-ssa/pr19476-2.C	(working copy)
@@ -1,5 +1,6 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-options "-O2 -fdump-tree-optimized -fdelete-null-pointer-checks" } */
+/* { dg-skip-if "" keeps_null_pointer_checks } */
 
 #include <new>
 
Index: gcc/testsuite/g++.dg/tree-ssa/pr19476-5.C
===================================================================
--- gcc/testsuite/g++.dg/tree-ssa/pr19476-5.C	(revision 221677)
+++ gcc/testsuite/g++.dg/tree-ssa/pr19476-5.C	(working copy)
@@ -1,5 +1,6 @@
 /* { dg-do compile } */
-/* { dg-options "-O -fdump-tree-ccp1" } */
+/* { dg-options "-O -fdump-tree-ccp1 -fdelete-null-pointer-checks" } */
+/* { dg-skip-if "" keeps_null_pointer_checks } */
 
 // See pr19476-1.C for a version that includes <new>.
 
Index: gcc/testsuite/g++.dg/tree-ssa/pr26406.C
===================================================================
--- gcc/testsuite/g++.dg/tree-ssa/pr26406.C	(revision 221677)
+++ gcc/testsuite/g++.dg/tree-ssa/pr26406.C	(working copy)
@@ -1,5 +1,6 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* { dg-options "-O2 -fdump-tree-optimized -fdelete-null-pointer-checks" } */
+/* { dg-skip-if "" keeps_null_pointer_checks } */
 
 int *f(int *b)
 {

Re: [rfc, stage 1] default to -fno-delete-null-pointer-checks on nios2-elf

[Sandra Loosemore]

Ping?

https://gcc.gnu.org/ml/gcc-patches/2015-03/msg01510.html

-Sandra

Re: [rfc, stage 1] default to -fno-delete-null-pointer-checks on nios2-elf

[Jeff Law]

On 03/29/2015 01:30 PM, Sandra Loosemore wrote:
> As the outcome of this discussion last month about unexpected behavior
> of -fisolate-erroneous-paths-dereference
>
> https://gcc.gnu.org/ml/gcc/2015-02/msg00163.html
>
> Altera has asked us to turn off -fdelete-null-pointer-checks on
> nios2-elf targets.  Presently, the AVR and CR16 back ends completely
> disable this option, but it seems to me that a better solution is to
> simply default it to off.  That's what the attached patch does for
> nios2, with appropriate adjustments to the testsuite.
>
> The rationale for defaulting to -fno-delete-null-pointer-checks on a
> bare-metal target is that it is the "safe" setting on targets where 0 is
> a valid memory address, and where the hardware may even require
> placement of e.g. a reset vector at that address.  Also, library code
> should be built to be "safe", especially things like memcpy that might
> be used by implicit compiler-generated calls.
>
> The rationale for allowing the default to be overridden on the command
> line, instead of disabling -fdelete-null-pointer-checks entirely, is
> that it's much more common for programs *not* to manipulate code or data
> at address 0, and we can generate smaller/faster code by enabling the
> option.
>
> So....
>
> (1) Is the change to the default for this flag in common.opt OK?  I
> verified that all existing uses just check for zero/non-zero-ness.
>
> (2) If the AVR and CR16 maintainers agree that defaulting the option to
> off rather than being completely disabling it is a better solution for
> their targets, too, I think being consistent across the three targets
> would simplify ongoing support -- e.g., the testsuite bits could be
> greatly simplified by getting rid of
> check_effective_target_keeps_null_pointer_checks and checks for
> keeps_null_pointer_checks entirely.  WDYT?
>
> I haven't done a full bootstrap with this patch yet....  I'd just like
> to get it out there for discussion to see if there is consensus that
> this is a reasonable approach, first.  This is stage 1 material in any
> case.
It looks very sane to me.  This is probably how the AVR and CR16 should 
have been handled to begin with IMHO.

FWIW, I generally discourage ports overriding default options, but this 
is a case where I believe it makes some sense.

Please move forward with an official submission.

jeff

Re: [rfc, stage 1] default to -fno-delete-null-pointer-checks on nios2-elf

[Sandra Loosemore]

Re https://gcc.gnu.org/ml/gcc-patches/2015-03/msg01510.html :

On 04/15/2015 10:42 PM, Jeff Law wrote:
> It looks very sane to me.  This is probably how the AVR and CR16 should
> have been handled to begin with IMHO.
>
> FWIW, I generally discourage ports overriding default options, but this
> is a case where I believe it makes some sense.
>
> Please move forward with an official submission.

I've now bootstrapped and regression-tested the previously posted patch 
on x86_64-linux-gnu, as well as retesting it on nios2-elf after updating 
my source tree to current mainline head.

Are the target-independent parts OK to commit?

-Sandra

Re: [rfc, stage 1] default to -fno-delete-null-pointer-checks on nios2-elf

[Jeff Law]

On 05/01/2015 02:33 PM, Sandra Loosemore wrote:
> Re https://gcc.gnu.org/ml/gcc-patches/2015-03/msg01510.html :
>
> On 04/15/2015 10:42 PM, Jeff Law wrote:
>> It looks very sane to me.  This is probably how the AVR and CR16 should
>> have been handled to begin with IMHO.
>>
>> FWIW, I generally discourage ports overriding default options, but this
>> is a case where I believe it makes some sense.
>>
>> Please move forward with an official submission.
>
> I've now bootstrapped and regression-tested the previously posted patch
> on x86_64-linux-gnu, as well as retesting it on nios2-elf after updating
> my source tree to current mainline head.
>
> Are the target-independent parts OK to commit?
Yes.  Please install.

Thanks,
Jeff