The following patch fixes
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70689
The patch was successfully tested and bootstrapped on x86/x86-64.
Committed to the trunk as rev. 235184.
Index: ChangeLog
===================================================================
--- ChangeLog (revision 235182)
+++ ChangeLog (working copy)
@@ -1,3 +1,11 @@
+2016-04-18 Vladimir Makarov <vmaka...@redhat.com>
+
+ PR middle-end/70689
+ * lra-constraints.c (equiv_substition_p): New.
+ (process_alt_operands): Use it.
+ (swap_operands): Swap it.
+ (curr_insn_transform): Update it.
+
2016-04-18 Michael Matz <m...@suse.de>
* tree.h (TYPE_ALIGN, DECL_ALIGN): Return shifted amount.
Index: testsuite/ChangeLog
===================================================================
--- testsuite/ChangeLog (revision 235182)
+++ testsuite/ChangeLog (working copy)
@@ -1,3 +1,8 @@
+2016-04-18 Vladimir Makarov <vmaka...@redhat.com>
+
+ PR middle-end/70689
+ * testsuite/gcc.target/i386/pr70689.c: New.
+
2016-04-18 H.J. Lu <hongjiu...@intel.com>
PR target/70708
Index: lra-constraints.c
===================================================================
--- lra-constraints.c (revision 235176)
+++ lra-constraints.c (working copy)
@@ -1258,6 +1258,10 @@ static bool goal_alt_swapped;
/* The chosen insn alternative. */
static int goal_alt_number;
+/* True if the corresponding operand is the result of an equivalence
+ substitution. */
+static bool equiv_substition_p[MAX_RECOG_OPERANDS];
+
/* The following five variables are used to choose the best insn
alternative. They reflect final characteristics of the best
alternative. */
@@ -2064,7 +2068,10 @@ process_alt_operands (int only_alternati
memory, or make other memory by reloading the
address like for 'o'. */
if (CONST_POOL_OK_P (mode, op)
- || MEM_P (op) || REG_P (op))
+ || MEM_P (op) || REG_P (op)
+ /* We can restore the equiv insn by a
+ reload. */
+ || equiv_substition_p[nop])
badop = false;
constmemok = true;
offmemok = true;
@@ -3371,6 +3378,7 @@ swap_operands (int nop)
std::swap (curr_operand_mode[nop], curr_operand_mode[nop + 1]);
std::swap (original_subreg_reg_mode[nop], original_subreg_reg_mode[nop + 1]);
std::swap (*curr_id->operand_loc[nop], *curr_id->operand_loc[nop + 1]);
+ std::swap (equiv_substition_p[nop], equiv_substition_p[nop + 1]);
/* Swap the duplicates too. */
lra_update_dup (curr_id, nop);
lra_update_dup (curr_id, nop + 1);
@@ -3473,8 +3481,10 @@ curr_insn_transform (bool check_only_p)
old = SUBREG_REG (old);
subst = get_equiv_with_elimination (old, curr_insn);
original_subreg_reg_mode[i] = VOIDmode;
+ equiv_substition_p[i] = false;
if (subst != old)
{
+ equiv_substition_p[i] = true;
subst = copy_rtx (subst);
lra_assert (REG_P (old));
if (GET_CODE (op) != SUBREG)
Index: testsuite/gcc.target/i386/pr70689.c
===================================================================
--- testsuite/gcc.target/i386/pr70689.c (revision 0)
+++ testsuite/gcc.target/i386/pr70689.c (working copy)
@@ -0,0 +1,27 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target ia32 } */
+/* { dg-options "-O1" } */
+
+struct S
+{
+ int f;
+};
+
+double a;
+int c;
+
+static
+void fn1 (struct S *p1)
+{
+ for (; c; )
+ if (p1->f++)
+ a = (int) p1;
+}
+
+int
+main ()
+{
+ struct S b = { 0 };
+ fn1 (&b);
+ return 0;
+}
