[PATCH] Add a trie to map quickly from address range to compilation unit.

[Alan Modra]

On Wed, Mar 23, 2022 at 11:24:20PM +0100, Steinar H. Gunderson via Binutils wrote:
> But I noticed something else that's probably not good in the existing
> code; the “found” variable leaks out of the loop from the last iteration
> (only). So if you find a match without a line number of the
> second-to-last compilation unit but not in the last, found = false on
> return, but if you find a similar match in the last compilation unit,
> found = true.
> 
> I suppose this isn't intentional, but what is the intention? Should
> there be a “found = false;” before the test on *linenumber_ptr?

Huh, I remember looking at this code a while ago and finding it
confusing.  I think the code would be clearer, and behave the same on
normal line number info with the following patch:

	* dwarf2.c (_bfd_dwarf2_find_nearest_line): Simplify setting of
	"found" in loop checking previous comp units with
	comp_unit_contains_address.

diff --git a/bfd/dwarf2.c b/bfd/dwarf2.c
index 8b5ac6012e1..ca8403da6da 100644
--- a/bfd/dwarf2.c
+++ b/bfd/dwarf2.c
@@ -5195,16 +5195,16 @@ _bfd_dwarf2_find_nearest_line (bfd *abfd,
 
       for (each = stash->f.all_comp_units; each; each = each->next_unit)
 	{
-	  bfd_vma range = (bfd_vma) -1;
-
-	  found = ((each->arange.high == 0
-		    || comp_unit_contains_address (each, addr))
-		   && (range = (comp_unit_find_nearest_line
-				(each, addr, &local_filename,
-				 &local_function, &local_linenumber,
-				 &local_discriminator))) != 0);
-	  if (found)
+	  bfd_vma range;
+
+	  if ((each->arange.high == 0
+	       || comp_unit_contains_address (each, addr))
+	      && (range = (comp_unit_find_nearest_line
+			   (each, addr, &local_filename,
+			    &local_function, &local_linenumber,
+			    &local_discriminator))) != 0)
 	    {
+	      found = true;
 	      /* PRs 15935 15994: Bogus debug information may have provided us
 		 with an erroneous match.  We attempt to counter this by
 		 selecting the match that has the smallest address range
@@ -5231,11 +5231,8 @@ _bfd_dwarf2_find_nearest_line (bfd *abfd,
 	    }
 	}
 
-      if (* linenumber_ptr)
-	{
-	  found = true;
-	  goto done;
-	}
+      if (found)
+	goto done;
     }
 
   /* Read each remaining comp. units checking each as they are read.  */

-- 
Alan Modra
Australia Development Lab, IBM