As the rtl.texi documentation of RTX_AUTOINC expressions says:
If a register used as the operand of these expressions is used in
another address in an insn, the original value of the register is
used. Uses of the register outside of an address are not permitted
within the same insn as a use in an embedded side effect expression
because such insns behave differently on different machines and hence
must be treated as ambiguous and disallowed.
late-combine was failing to follow this rule. One option would have
been to enforce it during the substitution phase, like combine does.
This could either be a dedicated condition in the substitution code
or, more generally, an extra condition in can_merge_accesses.
(The latter would include extending is_pre_post_modify to uses.)
However, since the restriction applies to patterns rather than to
actions on patterns, the more robust fix seemed to be test and reject
this case in (a subroutine of) rtl_ssa::recog. We already do something
similar for hard-coded register clobbers.
Using vec_rtx_properties isn't the lightest-weight operation
out there. I did wonder about relying on the is_pre_post_modify
flag of the definitions in the new_defs array, but that would
require callers that create new autoincs to set the flag before
calling recog. Normally these flags are instead updated
automatically based on the final pattern.
Besides, recog itself has had to traverse the whole pattern,
and it is even less light-weight than vec_rtx_properties.
At least the pattern should be in cache.
Tested on arm-linux-gnueabihf, aarch64-linux-gnu and
x86_64-linux-gnu. OK for trunk and backports?
Richard
gcc/
PR rtl-optimization/120347
* rtl-ssa/changes.cc (recog_level2): Check whether an
RTX_AUTOINCed register also appears outside of an address.
gcc/testsuite/
PR rtl-optimization/120347
* gcc.dg/torture/pr120347.c: New test.
---
gcc/rtl-ssa/changes.cc | 18 ++++++++++++++++++
gcc/testsuite/gcc.dg/torture/pr120347.c | 13 +++++++++++++
2 files changed, 31 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/torture/pr120347.c
diff --git a/gcc/rtl-ssa/changes.cc b/gcc/rtl-ssa/changes.cc
index eb579ad3ad7..f7aa6a66cdf 100644
--- a/gcc/rtl-ssa/changes.cc
+++ b/gcc/rtl-ssa/changes.cc
@@ -1106,6 +1106,24 @@ recog_level2 (insn_change &change, add_regno_clobber_fn
add_regno_clobber)
}
}
+ // Per rtl.texi, registers that are modified using RTX_AUTOINC operations
+ // cannot also appear outside an address.
+ vec_rtx_properties properties;
+ properties.add_pattern (pat);
+ for (rtx_obj_reference def : properties.refs ())
+ if (def.is_pre_post_modify ())
+ for (rtx_obj_reference use : properties.refs ())
+ if (def.regno == use.regno && !use.in_address ())
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "register %d is both auto-modified"
+ " and used outside an address:\n", def.regno);
+ print_rtl_single (dump_file, pat);
+ }
+ return false;
+ }
+
// check_asm_operands checks the constraints after RA, so we don't
// need to do it again.
if (reload_completed && !asm_p)
diff --git a/gcc/testsuite/gcc.dg/torture/pr120347.c
b/gcc/testsuite/gcc.dg/torture/pr120347.c
new file mode 100644
index 00000000000..a2d187bbc5c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr120347.c
@@ -0,0 +1,13 @@
+/* { dg-do assemble } */
+/* { dg-additional-options "-march=armv7-a -mthumb" { target { arm_arch_v7a_ok
&& arm_thumb2_ok } } } */
+
+void *end;
+void **start;
+void main(void)
+{
+ for (; end; start++) {
+ if (*start)
+ return;
+ *start = start;
+ }
+}
--
2.43.0
