Hi,
this is a duplication of volatile loads introduced during GCC 9 development by
the new 2->2 mechanism of the RTL combiner. There is already a substantial
checking for volatile references in can_combine_p but it implicitly assumes
that the combination reduces the number of instructions, which is of course
not the case here. So the fix teaches try_combine to abort the combination
when it is about to make a copy of volatile references to preserve them.
Bootstrapped/regtested on x86-64/Linux, OK for mainline and release branches?
2021-09-16 Eric Botcazou
PR rtl-optimization/102306
* combine.c (try_combine): Abort the combination if we are about
to duplicate volatile references.
2021-09-16 Eric Botcazou
* gcc.target/sparc/20210916-1.c: New test.
--
Eric Botcazoudiff --git a/gcc/combine.c b/gcc/combine.c
index 290a3667c65..892c834a160 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -3063,6 +3063,16 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
return 0;
}
+ /* We cannot safely duplicate volatile references in any case. */
+
+ if ((added_sets_2 && volatile_refs_p (PATTERN (i2)))
+ || (added_sets_1 && volatile_refs_p (PATTERN (i1)))
+ || (added_sets_0 && volatile_refs_p (PATTERN (i0
+{
+ undo_all ();
+ return 0;
+}
+
/* Count how many auto_inc expressions there were in the original insns;
we need to have the same number in the resulting patterns. */
/* { dg-do compile } */
/* { dg-require-effective-target ilp32 } */
/* { dg-options "-O -mcpu=v8" } */
extern void foo (void);
void test (volatile unsigned char *a)
{
char b = *a;
if (!b)
return;
if (b & 2)
foo ();
}
/* { dg-final { scan-assembler-times "ldub" 1 } } */
