[gcc r17-3391] [AutoFDO] Walk predecessor edges for PHI arguments in match

https://gcc.gnu.org/g:01cbfb28f7140f5a6089151b98bdf6a15532fda6

commit r17-3391-g01cbfb28f7140f5a6089151b98bdf6a15532fda6
Author: Kugan Vivekanandarajah <[email protected]>
Date:   Wed Aug 19 08:30:08 2026 +1000

    [AutoFDO] Walk predecessor edges for PHI arguments in match
    
    PHI arguments are indexed by incoming edges.  function_instance::match
    walked successor edges and could fail gimple_phi_arg_def_from_edge's
    destination assertion during afdo_offline.
    
    Regression tested on aarch64-linux-gnu with no new regressions
    Signed-off-by: Kugan Vivekanandarajah <[email protected]>
    
    gcc/ChangeLog:
    
    2026-08-19  Kugan Vivekanandarajah  <[email protected]>
    
            * auto-profile.cc (function_instance::match): Walk predecessor edges
            for PHI arguments.

Diff:
---
 gcc/auto-profile.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/auto-profile.cc b/gcc/auto-profile.cc
index 6aa5166c748b..324a26cefc8c 100644
--- a/gcc/auto-profile.cc
+++ b/gcc/auto-profile.cc
@@ -1764,7 +1764,8 @@ function_instance::match (cgraph_node *node,
 	  gcc_assert (!info);
 	  dump_stmt (phi, info, NULL, stack);
 	  counts.add (info);
-	  for (edge e : bb->succs)
+	  /* PHI arguments are indexed by incoming (predecessor) edges.  */
+	  for (edge e : bb->preds)
 	    {
 	      location_t phi_loc
 		= gimple_phi_arg_location_from_edge (phi, e);