Restore RTL alias analysis for hard frame pointer

The change:

	2021-07-28  Bin Cheng  <bin.cheng@linux.alibaba.com>

	alias.c (init_alias_analysis): Don't skip prologue/epilogue.

broke the alias analysis for the hard frame pointer (when it is used as a
frame pointer, i.e. when the frame pointer is not eliminated) described in
the large comment at the top of the file, because static_reg_base_value is
set for it and, consequently, new_reg_base_value too.

When the instruction saving the stack pointer into the hard frame pointer in
the prologue is processed, it is viewed as a second set of the hard frame
pointer and to a different value by record_set, which then proceeds to reset
new_reg_base_value to 0 and the game is over.

gcc/
	* alias.cc (init_alias_analysis): Do not record sets to the hard
	frame pointer if the frame pointer has not been eliminated.

diff --git a/gcc/alias.cc b/gcc/alias.cc
index d54feb1526876386716a7f54225abe9467db30eb..c62837dd854fb4e693eeafea9033b38ca9010b7a 100644 (file)
--- a/gcc/alias.cc
+++ b/gcc/alias.cc
@@ -3369,6 +3369,10 @@ memory_modified_in_insn_p (const_rtx mem, const_rtx insn)
 void
 init_alias_analysis (void)
 {
+  const bool frame_pointer_eliminated
+    = reload_completed
+      && !frame_pointer_needed
+      && targetm.can_eliminate (FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM);
   unsigned int maxreg = max_reg_num ();
   int changed, pass;
   int i;
@@ -3446,12 +3450,8 @@ init_alias_analysis (void)
       for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
        if (static_reg_base_value[i]
            /* Don't treat the hard frame pointer as special if we
-              eliminated the frame pointer to the stack pointer instead.  */
-           && !(i == HARD_FRAME_POINTER_REGNUM
-                && reload_completed
-                && !frame_pointer_needed
-                && targetm.can_eliminate (FRAME_POINTER_REGNUM,
-                                          STACK_POINTER_REGNUM)))
+              eliminated the frame pointer to the stack pointer.  */
+           && !(i == HARD_FRAME_POINTER_REGNUM && frame_pointer_eliminated))
          {
            new_reg_base_value[i] = static_reg_base_value[i];
            bitmap_set_bit (reg_seen, i);
@@ -3467,10 +3467,15 @@ init_alias_analysis (void)
                {
                  rtx note, set;
 
+                 /* Treat the hard frame pointer as special unless we
+                    eliminated the frame pointer to the stack pointer.  */
+                 if (!frame_pointer_eliminated
+                     && modified_in_p (hard_frame_pointer_rtx, insn))
+                   continue;
+
                  /* If this insn has a noalias note, process it,  Otherwise,
                     scan for sets.  A simple set will have no side effects
                     which could change the base value of any other register.  */
-
                  if (GET_CODE (PATTERN (insn)) == SET
                      && REG_NOTES (insn) != 0
                      && find_reg_note (insn, REG_NOALIAS, NULL_RTX))