[gcc r12-10554] [PR111497][LRA]: Copy substituted equivalence

[Richard Biener]

https://gcc.gnu.org/g:959cef942508b818c7dcb8df0f3c7bf4968d406a

commit r12-10554-g959cef942508b818c7dcb8df0f3c7bf4968d406a
Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Mon Sep 25 16:19:50 2023 -0400

    [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:
---
 gcc/lra-constraints.cc                   |  5 +++++
 gcc/lra.cc                               |  5 ++---
 gcc/testsuite/g++.target/i386/pr111497.C | 22 ++++++++++++++++++++++
 3 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index d92ab76908c8..04b0b6fbfc2a 100644
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -5139,6 +5139,11 @@ 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 1444cb759144..5e29d3270d7d 100644
--- 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
index 000000000000..a645bb95907e
--- /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++;
+}