[gcc r14-8086] gccrs: borrowck: Dump: handle infinite loops

[gcc r14-8086] gccrs: borrowck: Dump: handle infinite loops

[Arthur Cohen]

https://gcc.gnu.org/g:4c65919e19ca670b200718c0c37d24a9111fe4b9

commit r14-8086-g4c65919e19ca670b200718c0c37d24a9111fe4b9
Author: Jakub Dupak <dev@jakubdupak.com>
Date:   Thu Oct 19 11:04:29 2023 +0200

    gccrs: borrowck: Dump: handle infinite loops
    
    gcc/rust/ChangeLog:
    
            * checks/errors/borrowck/rust-bir-dump.cc (simplify_cfg): Detech infinite loops.
    
    Signed-off-by: Jakub Dupak <dev@jakubdupak.com>

Diff:
---
 gcc/rust/checks/errors/borrowck/rust-bir-dump.cc | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/gcc/rust/checks/errors/borrowck/rust-bir-dump.cc b/gcc/rust/checks/errors/borrowck/rust-bir-dump.cc
index ba530983dad..66870ddeb56 100644
--- a/gcc/rust/checks/errors/borrowck/rust-bir-dump.cc
+++ b/gcc/rust/checks/errors/borrowck/rust-bir-dump.cc
@@ -1,5 +1,6 @@
 #include <numeric>
 #include "rust-bir-dump.h"
+#include "rust-diagnostics.h"
 
 namespace Rust {
 namespace BIR {
@@ -76,7 +77,21 @@ simplify_cfg (Function &func, std::vector<BasicBlockId> &bb_fold_map)
 	  const BasicBlock &bb = func.basic_blocks[bb_fold_map[i]];
 	  if (bb.statements.empty () && bb.is_goto_terminated ())
 	    {
-	      bb_fold_map[i] = bb.successors.at (0);
+	      auto dst = bb.successors.at (0);
+	      if (bb_fold_map[dst] != dst)
+		{
+		  rust_error_at (
+		    UNKNOWN_LOCATION,
+		    "BIR DUMP: Cannot fold CFG, because it contains an "
+		    "infinite loop with no executable statements.");
+		  rust_inform (UNKNOWN_LOCATION,
+			       "Continuing with an unfolded CFG.");
+		  // Reverting the fold map to the original state.
+		  std::iota (bb_fold_map.begin (), bb_fold_map.end (), 0);
+		  stabilized = true;
+		  break;
+		}
+	      bb_fold_map[i] = dst;
 	      stabilized = false;
 	    }
 	}