Hi!
The r241060 change added the second hunk in this patch which the patch is
reverting. The problem is that not deleting some unmarked insns in
delete_unmarked_insns is done in a wrong place, it causes indeed not to
delete the instruction we don't want to DCE, but the instructions that
are needed by the instructions (in this case a memory load whose result
the REG_CFA_RESTORE instruction uses) are not marked either and those are
deleted.
The following patch fixes it by making such instructions non-deletable,
which means they are marked and the DCE algorithm then marks the
instructions they need too.
Bootstrapped/regtested on {x86_64,i686,powerpc64{,le}}-linux, ok for trunk?
2018-01-25 Jakub Jelinek
PR rtl-optimization/83985
* dce.c (deletable_insn_p): Return false for separate shrink wrapping
REG_CFA_RESTORE insns.
(delete_unmarked_insns): Don't ignore separate shrink wrapping
REG_CFA_RESTORE insns here.
* gcc.dg/pr83985.c: New test.
--- gcc/dce.c.jj2018-01-04 00:43:17.995703342 +0100
+++ gcc/dce.c 2018-01-25 17:55:49.750007894 +0100
@@ -131,6 +131,12 @@ deletable_insn_p (rtx_insn *insn, bool f
&& REGNO (pic_offset_table_rtx) >= FIRST_PSEUDO_REGISTER)
return false;
+ /* Callee-save restores are needed. */
+ if (RTX_FRAME_RELATED_P (insn)
+ && crtl->shrink_wrapped_separate
+ && find_reg_note (insn, REG_CFA_RESTORE, NULL))
+return false;
+
body = PATTERN (insn);
switch (GET_CODE (body))
{
@@ -592,15 +598,6 @@ delete_unmarked_insns (void)
if (!dbg_cnt (dce))
continue;
- if (crtl->shrink_wrapped_separate
- && find_reg_note (insn, REG_CFA_RESTORE, NULL))
- {
- if (dump_file)
- fprintf (dump_file, "DCE: NOT deleting insn %d, it's a "
- "callee-save restore\n", INSN_UID (insn));
- continue;
- }
-
if (dump_file)
fprintf (dump_file, "DCE: Deleting insn %d\n", INSN_UID (insn));
--- gcc/testsuite/gcc.dg/pr83985.c.jj 2018-01-25 18:05:23.366121812 +0100
+++ gcc/testsuite/gcc.dg/pr83985.c 2018-01-25 18:05:03.513117871 +0100
@@ -0,0 +1,25 @@
+/* PR rtl-optimization/83985 */
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-additional-options "-mcpu=e300c3 -mtune=e300c3" { target {
powerpc*-*-* && ilp32 } } } */
+
+long long int v;
+
+void
+foo (int x)
+{
+ if (x == 0)
+return;
+
+ while (v < 2)
+{
+ signed char *a;
+ v /= x;
+ a = v == 0 ? (signed char *) : (signed char *)
+ ++*a;
+ ++v;
+}
+
+ while (1)
+;
+}
Jakub
