[PATCH 4 of 4] Add hierarchical discriminator for loop unrolling

[Jan Hubicka]

> I would like to again ping the patch posted in https://gcc.gnu.org/pipermail/gcc-patches/2025-November/700704.html
> 
> Add hierarchical discriminator support for loop unrolling.
> Assigns multiplicity and copyid discriminators to distinguish unrolled
> iterations.
> 
> gcc/ChangeLog:
> 
>         * cfgloopmanip.cc (duplicate_loop_body_to_header_edge): Assign
>         hierarchical discriminators for loop unrolling.
>         * cfgloopmanip.h (DLTHE_RECORD_HIERARCHICAL_DISCRIMINATOR): New flag.
>         * tree-ssa-loop-ivcanon.cc (try_unroll_loop_completely): Pass flag
>         to enable hierarchical discriminator assignment.
>         (try_peel_loop): Likewise.
> 
> gcc/testsuite/ChangeLog:
> 
>         * gcc.dg/hierarchical-discriminator-unroll.c: New test.

+  unsigned int loop_copyid_base = 0;
+  if (current_ir_type () == IR_GIMPLE)
+    {
..
+    }
+  else
+    {
+      /* For RTL, try to find an instruction with a valid location.
+	 Be defensive to avoid crashes on invalid/corrupted insns.  */
+      rtx_insn *insn = BB_END (loop->header);
+      while (insn && insn != BB_HEAD (loop->header))
+	{
+	  /* Only check location if this is a valid insn.  */
+	  if (INSN_P (insn))
+	    {
+	      location_t loc = INSN_LOCATION (insn);
+	      if (loc != UNKNOWN_LOCATION)
+		{
+		  loop_loc = get_pure_location (loc);
+		  break;
+		}
+	    }
+	  insn = PREV_INSN (insn);
+	}
+    }
+
...
+	  if (current_ir_type () == IR_GIMPLE)
+	    {
....
+	    }
+	  else
+	    {
+	      /* Only assign discriminators if we successfully allocated
+		 a copyid base.  */
+	      if (loop_copyid_base > 0)

This will never be true.  But I think the copyid allocation can work
both on RTL and Gimple.  You will need to support initializing the
allocator at RTL level too if necessary, but both is just a siple walk
of a function body.


Honza