[patch] Fix PR rtl-optimization/100411

[Eric Botcazou]

Hi,

this is the bootstrap failure of GCC 11 on MinGW64 configured with --enable-
tune=nocona.  The bottom line is that SEH does not support CFI for epilogues 
but the x86 back-end nevertheless attaches it to instructions, so we have to 
filter it out and this is done by detecting the end of the prologue by means 
of the NOTE_INSN_PROLOGUE_END note.

But the compiler manages to generate a second epilogue before this note in the 
RTL stream and this fools the above logic.  The root cause is cross-jumping, 
which inserts a jump before the end of the prologue (in fact just before the 
note); the rest (CFG cleanup, BB reordering) is downhill from there.

Tested on x86-64/Linux and x86-64/Windows, OK for mainline and 11 branch?


2021-05-05  Eric Botcazou  <ebotca...@adacore.com>

        PR rtl-optimization/100411
        * cfgcleanup.c (try_crossjump_to_edge): Also skip end of prologue
        and beginning of function markers.

-- 
Eric Botcazou
diff --git a/gcc/cfgcleanup.c b/gcc/cfgcleanup.c
index f05cb6136c7..64279cc8c20 100644
--- a/gcc/cfgcleanup.c
+++ b/gcc/cfgcleanup.c
@@ -2148,6 +2148,20 @@ try_crossjump_to_edge (int mode, edge e1, edge e2,
   while (DEBUG_INSN_P (newpos1))
     newpos1 = NEXT_INSN (newpos1);
 
+  /* And end of prologue marker.  */
+  if (NOTE_P (newpos1) && NOTE_KIND (newpos1) == NOTE_INSN_PROLOGUE_END)
+    newpos1 = NEXT_INSN (newpos1);
+
+  while (DEBUG_INSN_P (newpos1))
+    newpos1 = NEXT_INSN (newpos1);
+
+  /* And also beginning of function marker.  */
+  if (NOTE_P (newpos1) && NOTE_KIND (newpos1) == NOTE_INSN_FUNCTION_BEG)
+    newpos1 = NEXT_INSN (newpos1);
+
+  while (DEBUG_INSN_P (newpos1))
+    newpos1 = NEXT_INSN (newpos1);
+
   redirect_from = split_block (src1, PREV_INSN (newpos1))->src;
   to_remove = single_succ (redirect_from);