[PR111497][LRA]: Copy substituted equivalence

When we substitute the equivalence and it becomes shared, we can fail
to correctly update reg info used by LRA.  This can result in wrong
code generation, e.g. because of incorrect live analysis.  It can also
result in compiler crash as the pseudo survives RA.  This is what
exactly happened for the PR.  This patch solves this problem by
unsharing substituted equivalences.

gcc/ChangeLog:

	PR middle-end/111497
	* lra-constraints.cc (lra_constraints): Copy substituted
	equivalence.
	* lra.cc (lra): Change comment for calling unshare_all_rtl_again.

gcc/testsuite/ChangeLog:

	PR middle-end/111497
	* g++.target/i386/pr111497.C: new test.

(cherry picked from commit 3c23defed384cf17518ad6c817d94463a445d21b)

diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index ff4e8f06063682e4e240701e389e5014323ea0e8..21f05df0d618d4503c55baa84c4aca993f2ddc12 100644 (file)
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -5271,6 +5271,11 @@ lra_constraints (bool first_p)
                                           loc_equivalence_callback, curr_insn);
              if (old != *curr_id->operand_loc[0])
                {
+                 /* If we substitute pseudo by shared equivalence, we can fail
+                    to update LRA reg info and this can result in many
+                    unexpected consequences.  So keep rtl unshared:  */
+                 *curr_id->operand_loc[0]
+                   = copy_rtx (*curr_id->operand_loc[0]);
                  lra_update_insn_regno_info (curr_insn);
                  changed_p = true;
                }

diff --git a/gcc/lra.cc b/gcc/lra.cc
index eb3ee1f8b63a78f0b0b6a614236d1adaee84375d..b2c2af079d932524a758622d885cec68b588851a 100644 (file)
--- a/gcc/lra.cc
+++ b/gcc/lra.cc
@@ -2535,9 +2535,8 @@ lra (FILE *f)
   if (inserted_p)
     commit_edge_insertions ();
 
-  /* Replacing pseudos with their memory equivalents might have
-     created shared rtx.  Subsequent passes would get confused
-     by this, so unshare everything here.  */
+  /* Subsequent passes expect that rtl is unshared, so unshare everything
+     here.  */
   unshare_all_rtl_again (get_insns ());
 
   if (flag_checking)

diff --git a/gcc/testsuite/g++.target/i386/pr111497.C b/gcc/testsuite/g++.target/i386/pr111497.C
new file mode 100644 (file)
index 0000000..a645bb9
--- /dev/null
+++ b/gcc/testsuite/g++.target/i386/pr111497.C
@@ -0,0 +1,22 @@
+// { dg-do compile { target ia32 } }
+// { dg-options "-march=i686 -mtune=generic -fPIC -O2 -g" }
+
+class A;
+struct B { const char *b1; int b2; };
+struct C : B { C (const char *x, int y) { b1 = x; b2 = y; } };
+struct D : C { D (B x) : C (x.b1, x.b2) {} };
+struct E { E (A *); };
+struct F : E { D f1, f2, f3, f4, f5, f6; F (A *, const B &, const B &, const B &); };
+struct G : F { G (A *, const B &, const B &, const B &); };
+struct H { int h; };
+struct I { H i; };
+struct J { I *j; };
+struct A : J {};
+inline F::F (A *x, const B &y, const B &z, const B &w)
+  : E(x), f1(y), f2(z), f3(w), f4(y), f5(z), f6(w) {}
+G::G (A *x, const B &y, const B &z, const B &w) : F(x, y, z, w)
+{
+  H *h = &x->j->i;
+  if (h)
+    h->h++;
+}