Improve shrink wrapping debug output

Currently if requires_stack_frame_p() returns true for some insn, the
shrink-wrapping debug output contains only the number of a block containing
that insn.

But it is very useful to see the particular insn that requires the prologue.
Let's call print_rtl_single to display that insn in the following pass dump.

gcc/

	* shrink-wrap.c (try_shrink_wrapping): Improve debug output.

1 files changed, 6 insertions, 1 deletions

diff --git a/gcc/shrink-wrap.c b/gcc/shrink-wrap.c
index 775db9c..d70635e 100644
--- a/gcc/shrink-wrap.c
+++ b/gcc/shrink-wrap.c
@@ -43,6 +43,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "rtl-iter.h"
 #include "valtrack.h"
 #include "function-abi.h"
+#include "print-rtl.h"
 
 /* Return true if INSN requires the stack frame to be set up.
    PROLOGUE_USED contains the hard registers used in the function
@@ -735,7 +736,11 @@ try_shrink_wrapping (edge *entry_edge, rtx_insn *prologue_seq)
 				       set_up_by_prologue.set))
 	  {
 	    if (dump_file)
-	      fprintf (dump_file, "Block %d needs the prologue.\n", bb->index);
+	      {
+		fprintf (dump_file, "Block %d needs prologue due to insn %d:\n",
+			 bb->index, INSN_UID (insn));
+		print_rtl_single (dump_file, insn);
+	      }
 	    pro = nearest_common_dominator (CDI_DOMINATORS, pro, bb);
 	    break;
 	  }