[PATCH] middle-end/106075 - non-call EH and DSE

[Richard Biener <rguenther@suse.de>]

The following fixes a long-standing bug with DSE removing stores as
dead even though they are live across non-call exceptional flow.
This affects both GIMPLE and RTL DSE and the fix is similar in
making externally throwing statements uses of non-local stores.
Note this doesn't fix the GIMPLE side when the throwing statement
does not involve a load or a store because then the statement does
not have virtual operands and thus is not visited by GIMPLE DSE.

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

This doesn't seem to be a regression and I'm unsure as to how
important it is for Ada (I consider it not important for C/C++),
so for now I'll queue it for next stage1.

	PR middle-end/106075
	* dse.cc (scan_insn): Consider externally throwing insns
	to read from not frame based memory.
	* tree-ssa-dse.cc (dse_classify_store): Consider externally
	throwing uses to read from global memory.

	* gcc.dg/torture/pr106075-1.c: New testcase.
---
 gcc/dse.cc                                |  5 ++++
 gcc/testsuite/gcc.dg/torture/pr106075-1.c | 36 +++++++++++++++++++++++
 gcc/tree-ssa-dse.cc                       |  8 ++++-
 3 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr106075-1.c

diff --git a/gcc/dse.cc b/gcc/dse.cc
index a2db8d1cc32..7e258b81f66 100644
--- a/gcc/dse.cc
+++ b/gcc/dse.cc
@@ -2633,6 +2633,11 @@ scan_insn (bb_info_t bb_info, rtx_insn *insn, int max_active_local_stores)
       return;
     }
 
+  /* An externally throwing statement may read any memory that is not
+     relative to the frame.  */
+  if (can_throw_external (insn))
+    add_non_frame_wild_read (bb_info);
+
   /* Assuming that there are sets in these insns, we cannot delete
      them.  */
   if ((GET_CODE (PATTERN (insn)) == CLOBBER)
diff --git a/gcc/testsuite/gcc.dg/torture/pr106075-1.c b/gcc/testsuite/gcc.dg/torture/pr106075-1.c
new file mode 100644
index 00000000000..b9affbf1082
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr106075-1.c
@@ -0,0 +1,36 @@
+/* { dg-do run { target *-*-linux* } } */
+/* { dg-additional-options "-fnon-call-exceptions" } */
+
+#include <unistd.h>
+#include <signal.h>
+#include <stdlib.h>
+
+int a = 1;
+short *b;
+void __attribute__((noipa))
+test()
+{
+  a=12345;
+  *b=0;
+  a=1;
+}
+
+void check (int i)
+{
+  if (a != 12345)
+    abort ();
+  exit (0);
+}
+
+int
+main ()
+{
+  struct sigaction s;
+  sigemptyset (&s.sa_mask);
+  s.sa_handler = check;
+  s.sa_flags = 0;
+  sigaction (SIGSEGV, &s, NULL);
+  test();
+  abort ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-dse.cc b/gcc/tree-ssa-dse.cc
index 46ab57d5754..b2e2359c3da 100644
--- a/gcc/tree-ssa-dse.cc
+++ b/gcc/tree-ssa-dse.cc
@@ -960,6 +960,7 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
   auto_bitmap visited;
   std::unique_ptr<data_reference, void(*)(data_reference_p)>
     dra (nullptr, free_data_ref);
+  bool maybe_global = ref_may_alias_global_p (ref, false);
 
   if (by_clobber_p)
     *by_clobber_p = true;
@@ -1038,6 +1039,11 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
 		      last_phi_def = as_a <gphi *> (use_stmt);
 		    }
 		}
+	      /* If the stmt can throw externally and the store is
+		 visible in the context unwound to the store is live.  */
+	      else if (maybe_global
+		       && stmt_can_throw_external (cfun, use_stmt))
+		return DSE_STORE_LIVE;
 	      /* If the statement is a use the store is not dead.  */
 	      else if (ref_maybe_used_by_stmt_p (use_stmt, ref))
 		{
@@ -1116,7 +1122,7 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
 	 just pretend the stmt makes itself dead.  Otherwise fail.  */
       if (defs.is_empty ())
 	{
-	  if (ref_may_alias_global_p (ref, false))
+	  if (maybe_global)
 	    return DSE_STORE_LIVE;
 
 	  if (by_clobber_p)
-- 
2.35.3