[PATCH 3/7] Add func to check if register is clobbered by clobber_high

[Alan Hayward]

This patch adds the function reg_is_clobbered_by_clobber_high.
Given a CLOBBER_HIGH expression and a register, it checks if
the register will be clobbered.

A second version exists for the cases where the expressions are
not available.

The function will be used throughout the following patches.

Alan.

2017-11-16  Alan Hayward  <alan.hayw...@arm.com>

        * rtl.h (reg_is_clobbered_by_clobber_high): Add declarations.
        * rtlanal.c (reg_is_clobbered_by_clobber_high): Add function.

diff --git a/gcc/rtl.h b/gcc/rtl.h
index 
bdb05d00120e7fadeb7f2d29bd67afc7a77262c1..5a85eb42ea4455cf3a975b3adbdb9d0415441d3b
 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -3417,6 +3417,16 @@ extern bool tablejump_p (const rtx_insn *, rtx_insn **, 
rtx_jump_table_data **);
 extern int computed_jump_p (const rtx_insn *);
 extern bool tls_referenced_p (const_rtx);
 extern bool contains_mem_rtx_p (rtx x);
+extern bool reg_is_clobbered_by_clobber_high (unsigned int, machine_mode,
+                                             const_rtx);
+
+/* Convenient wrapper for reg_is_clobbered_by_clobber_high.  */
+inline bool
+reg_is_clobbered_by_clobber_high (const_rtx x, const_rtx clobber_high_op)
+{
+  return reg_is_clobbered_by_clobber_high (REGNO (x), GET_MODE (x),
+                                          clobber_high_op);
+}

 /* Overload for refers_to_regno_p for checking a single register.  */
 inline bool
diff --git a/gcc/rtlanal.c b/gcc/rtlanal.c
index 
79a5ae197c14ba338240123f2fc912f2ea60e178..923e3314d25c05f9055907c61b4a24186701cc23
 100644
--- a/gcc/rtlanal.c
+++ b/gcc/rtlanal.c
@@ -6519,3 +6519,32 @@ tls_referenced_p (const_rtx x)
       return true;
   return false;
 }
+
+/* Return true if reg REGNO with mode REG_MODE would be clobbered by the
+   clobber_high operand in CLOBBER_HIGH_OP.  */
+
+bool
+reg_is_clobbered_by_clobber_high (unsigned int regno, machine_mode reg_mode,
+                                 const_rtx clobber_high_op)
+{
+  unsigned int clobber_regno = REGNO (clobber_high_op);
+  machine_mode clobber_mode = GET_MODE (clobber_high_op);
+  unsigned char regno_nregs = hard_regno_nregs (regno, reg_mode);
+
+  /* Clobber high should always span exactly one register.  */
+  gcc_assert (REG_NREGS (clobber_high_op) == 1);
+
+  /* Clobber high needs to match with one of the registers in X.  */
+  if (clobber_regno < regno || clobber_regno >= regno + regno_nregs)
+    return false;
+
+  gcc_assert (reg_mode != BLKmode && clobber_mode != BLKmode);
+
+  if (reg_mode == VOIDmode)
+    return clobber_mode != VOIDmode;
+
+  /* Clobber high will clobber if its size might be greater than the size of
+     register regno.  */
+  return may_gt (exact_div (GET_MODE_SIZE (reg_mode), regno_nregs),
+                GET_MODE_SIZE (clobber_mode));
+}