On Thu, 7 Mar 2024, Uros Bizjak wrote:
> The compiler, configured with --enable-checking=yes,rtl,extra ICEs with:
>
> internal compiler error: RTL check: expected elt 0 type 'e' or 'u',
> have 'E' (rtx unspec) in try_combine, at combine.cc:3237
>
> This is
>
> 3236 /* Just replace the CC reg with a new mode. */
> 3237 SUBST (XEXP (*cc_use_loc, 0), newpat_dest);
> 3238 undobuf.other_insn = cc_use_insn;
>
> in combine.cc, where *cc_use_loc is
>
> (unspec:DI [
> (reg:CC 17 flags)
> ] UNSPEC_PUSHFL)
>
> combine assumes CC must be used inside of a comparison and uses XEXP (..., 0)
> without checking on the RTX type of the argument.
>
> Undo the combination if *cc_use_loc is not COMPARISON_P.
>
> Also remove buggy and now redundant check for (const 0) RTX as part of
> the comparison.
>
> PR rtl-optimization/112560
>
> gcc/ChangeLog:
>
> * combine.cc (try_combine): Reject the combination
> if *cc_use_loc is not COMPARISON_P.
>
> Bootstrapped and regression tested on x86_64-pc-linux-gnu {,-m32}.
>
> OK for trunk?
Since you CCed me - looking at the code I wonder why we fatally fail.
The following might also fix the issue and preserve more of the
rest of the flow of the function.
If that works I'd prefer it. But I'll defer approval to the combine
maintainer which is Segher.
Thanks,
Richard.
diff --git a/gcc/combine.cc b/gcc/combine.cc
index a4479f8d836..e280cd72ec7 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -3182,7 +3182,8 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn
*i1, rtx_insn *i0,
if (undobuf.other_insn == 0
&& (cc_use_loc = find_single_use (SET_DEST (newpat), i3,
- &cc_use_insn)))
+ &cc_use_insn))
+ && COMPARISON_P (*cc_use_loc))
{
compare_code = orig_compare_code = GET_CODE (*cc_use_loc);
if (is_a <scalar_int_mode> (GET_MODE (i2dest), &mode))
@@ -3200,7 +3201,7 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn
*i1, rtx_insn *i0,
the above simplify_compare_const() returned a new comparison
operator. undobuf.other_insn is assigned the CC use insn
when modifying it. */
- if (cc_use_loc)
+ if (cc_use_loc && COMPARISON_P (*cc_use_loc))
{
#ifdef SELECT_CC_MODE
machine_mode new_mode
