The following patch fixes
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70478
The patch was successfully bootstrapped and tested on x86-64/ppc64/arm64.
Committed as rev. 246764.
Index: ChangeLog
===================================================================
--- ChangeLog (revision 246763)
+++ ChangeLog (working copy)
@@ -1,3 +1,9 @@
+2017-04-07 Vladimir Makarov <vmaka...@redhat.com>
+
+ PR rtl-optimization/70478
+ * lra-constraints.c (process_alt_operands): Disfavor alternative
+ insn memory operands.
+
2017-04-07 Jeff Law <l...@redhat.com>
* config/iq2000/iq2000.c (final_prescan_insn): Do not separate a
Index: testsuite/ChangeLog
===================================================================
--- testsuite/ChangeLog (revision 246763)
+++ testsuite/ChangeLog (working copy)
@@ -1,3 +1,8 @@
+2017-04-07 Vladimir Makarov <vmaka...@redhat.com>
+
+ PR rtl-optimization/70478
+ * gcc.target/s390/pr70478.c: New.
+
2017-04-07 Martin Liska <mli...@suse.cz>
PR target/79889
Index: lra-constraints.c
===================================================================
--- lra-constraints.c (revision 246763)
+++ lra-constraints.c (working copy)
@@ -2685,6 +2685,21 @@ process_alt_operands (int only_alternati
}
}
+ /* When we use memory operand, the insn should read the
+ value from memory and even if we just wrote a value
+ into the memory it is costly in comparison with an
+ insn alternative which does not use memory
+ (e.g. register or immediate operand). */
+ if (no_regs_p && offmemok)
+ {
+ if (lra_dump_file != NULL)
+ fprintf
+ (lra_dump_file,
+ " Using memory insn operand %d: reject+=3\n",
+ nop);
+ reject += 3;
+ }
+
#ifdef SECONDARY_MEMORY_NEEDED
/* If reload requires moving value through secondary
memory, it will need one more insn at least. */
Index: testsuite/gcc.target/s390/pr70478.c
===================================================================
--- testsuite/gcc.target/s390/pr70478.c (nonexistent)
+++ testsuite/gcc.target/s390/pr70478.c (working copy)
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-w -O3 -march=z9-109" } */
+/* { dg-final { scan-assembler-not "stg" } } */
+
+void foo(unsigned int *a, unsigned char *b)
+{
+ *a &= *b;
+}
