RFA: Fix PR41905 (ICE in lower_eh_constructs)

[Michael Matz]

Hi,

the problem here is that lower_eh_constructs_2 adds an assignment to a new 
temporary for throwing statements, which includes normals calls.  In the 
testcase that call happens to be noreturn, so adding the assignment 
changes the body from being not fallthru to a maybe-fallthru, but really 
require a non-fallthru body.

The easiest seems to simply not add this assigment for statements that 
can't fallthru.  Other options would be that the frontend or gimplifier 
emit a call to a noreturn function without a LHS.  To me the former looks 
more conservative.

It fixes the testcase, regstrapping on x86_64-linux in progress.  Okay if 
that passes?


Ciao,
Michael.
-- 
	* tree-eh.c (lower_eh_constructs_2): Don't add assignments
	below statements that can't fall thru.

testsuite/
	* g++.dg/tree-ssa/pr41905.C: New testcase.

Index: tree-eh.c
===================================================================
--- tree-eh.c	(revision 154672)
+++ tree-eh.c	(working copy)
@@ -1868,9 +1868,12 @@ lower_eh_constructs_2 (struct leh_state
     case GIMPLE_ASSIGN:
       /* If the stmt can throw use a new temporary for the assignment
          to a LHS.  This makes sure the old value of the LHS is
-	 available on the EH edge.  */
+	 available on the EH edge.  Only do so for statements that
+	 potentially fall thru (no noreturn calls e.g.), otherwise
+	 this new assignment might create fake fallthru regions.  */
       if (stmt_could_throw_p (stmt)
 	  && gimple_has_lhs (stmt)
+	  && gimple_stmt_may_fallthru (stmt)
 	  && !tree_could_throw_p (gimple_get_lhs (stmt))
 	  && is_gimple_reg_type (TREE_TYPE (gimple_get_lhs (stmt))))
 	{
Index: testsuite/g++.dg/tree-ssa/pr41905.C
===================================================================
--- testsuite/g++.dg/tree-ssa/pr41905.C	(revision 0)
+++ testsuite/g++.dg/tree-ssa/pr41905.C	(revision 0)
@@ -0,0 +1,4 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+int foo() __attribute__((noreturn));
+int bar() { return foo(); }