[gcc(refs/vendors/ARM/heads/morello)] Add -ffake-hybrid-init

[gcc(refs/vendors/ARM/heads/morello)] Add -ffake-hybrid-init

[Matthew Malcomson]

https://gcc.gnu.org/g:272ae0194290f681d19acffa2d03f4e1ea8b355d

commit 272ae0194290f681d19acffa2d03f4e1ea8b355d
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Thu Mar 3 16:06:50 2022 +0000

    Add -ffake-hybrid-init
    
    This patch adds -ffake-hybrid-init=N, to go with -ffake-hybrid=M.
    When both options are present, the semantics are:
    
      use __capability for decl i (counting from 0) if (N + i) % M == 0
    
    Otherwise the semantics of -ffake-hybrid=M are unchanged:
    
      randomly use __capability, with a probability of 1/M

Diff:
---
 gcc/c/c-decl.c               | 23 +++++++++++++++++++++--
 gcc/common.opt               |  4 ++++
 gcc/config/aarch64/aarch64.c |  4 ++--
 3 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index 1c30003d0d4..fc05a0163c6 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -5970,6 +5970,26 @@ smallest_type_quals_location (const location_t *locations,
   return loc;
 }
 
+/* Return true if -ffake-hybrid says that we should automatically
+   modify a piece of code.  */
+
+static bool
+test_fake_hybrid (void)
+{
+  static int fake_hybrid_counter;
+
+  if (!flag_fake_hybrid)
+    return false;
+
+  if (flag_fake_hybrid_init < flag_fake_hybrid)
+    {
+      int count = flag_fake_hybrid_init + fake_hybrid_counter++;
+      return (count % flag_fake_hybrid) == 0;
+    }
+
+  return (rand() % flag_fake_hybrid) == 0;
+}
+
 /* Given declspecs and a declarator,
    determine the name and type of the object declared
    and construct a ..._DECL node for it.
@@ -6983,8 +7003,7 @@ grokdeclarator (const struct c_declarator *declarator,
 	    type_quals = declarator->u.pointer_quals;
 
 	    declarator = declarator->declarator;
-	    if (flag_fake_hybrid
-		&& (rand() % flag_fake_hybrid) == 0)
+	    if (test_fake_hybrid ())
 	      {
 		capability_levels_in_declarator++;
 		tree attr_name = get_identifier ("cheri_capability");
diff --git a/gcc/common.opt b/gcc/common.opt
index a874b24842a..43581eb6d62 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1227,6 +1227,10 @@ Choose to do some fake hybrid capability stuff.
 This is largely in order to explore whether using hybrid capabilities will
 cause a lot of problems or not.
 
+ffake-hybrid-init=
+Common Joined RejectNegative UInteger Var(flag_fake_hybrid_init) Init(INT_MAX)
+Use a round-robin counter for -ffake-hybrid and specify its initial value.
+
 fdebug-prefix-map=
 Common Joined RejectNegative Var(common_deferred_options) Defer
 -fdebug-prefix-map=<old>=<new>	Map one directory name to another in debug information.
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 5f8419cfca0..6d159dec463 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -15157,8 +15157,8 @@ aarch64_override_options_internal (struct gcc_options *opts)
 	  error ("MORELLO TODO OpenACC has not been implemented for Morello");
   if (!flag_inline_atomics && TARGET_CAPABILITY_ANY)
 	  error ("MORELLO TODO -fno-inline-atomics has not been implemented for Morello");
-  if (flag_fake_hybrid)
-	  srand(get_random_seed(false));
+  if (flag_fake_hybrid >= flag_fake_hybrid_init)
+    srand (get_random_seed (false));
 
   if (TARGET_CAPABILITY_ANY && TARGET_SVE)
     error ("SVE is not supported with capabilities");