https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113010
--- Comment #6 from Greg McGary <gkm at rivosinc dot com> ---
(In reply to Andrew Pinski from comment #5)
> (In reply to Andrew Pinski from comment #4)
> > (In reply to Greg McGary from comment #3)
> > > This fixes it, though I would like second look from someone more familiar
> > > with the combiner:
> >
> > I almost sure this is still an issue with WORD_REGISTER_OPERATIONS .
>
> That is this is missing that check:
>
> ```
> /* Convert sign extension to zero extension, if we know that the high
> bit is not set, as this is easier to optimize. It will be converted
> back to cheaper alternative in make_extraction. */
> if (GET_CODE (x) == SIGN_EXTEND
> && HWI_COMPUTABLE_MODE_P (mode)
> && ((nonzero_bits (XEXP (x, 0), inner_mode)
> & ~(((unsigned HOST_WIDE_INT) GET_MODE_MASK (inner_mode)) >> 1))
> == 0))
>
> ```
>
> Should most likely need the same check as what was added in r14-6806 . And
> yes it a similar bug dealing with WORD_REGISTER_OPERATIONS which is why I
> thought it was the same.
I agree that it pertains to WORD_REGISTER_OPERATIONS. However, the check needs
to happen. The test for converting SIGN_EXTEND to ZERO_EXTEND is false for
MEM_P (x) already. The erroneous conversion to SUBREG happens farther down,
here:
```
modewidth = GET_MODE_PRECISION (mode);
if (modewidth >= pos + len)
{
=> tem = gen_lowpart (mode, XEXP (x, 0));
if (!tem || GET_CODE (tem) == CLOBBER)
return x;
tem = simplify_shift_const (NULL_RTX, ASHIFT, mode,
tem, modewidth - pos - len);
tem = simplify_shift_const (NULL_RTX, unsignedp ? LSHIFTRT : ASHIFTRT,
mode, tem, modewidth - len);
}
```
This fix honors WORD_REGISTER_OPERATIONS, and adds a test:
```
diff --git a/gcc/combine.cc b/gcc/combine.cc
index 812553c091e..ba587184dfc 100644
--- a/gcc/combine.cc
+++ b/gcc/combine.cc
@@ -7208,6 +7208,11 @@ expand_compound_operation (rtx x)
if (len == 0)
return x;
+ /* Sign-extending loads can never be simplified at compile time. */
+ if (WORD_REGISTER_OPERATIONS && MEM_P (XEXP (x, 0))
+ && load_extend_op (inner_mode) == SIGN_EXTEND)
+ return x;
+
break;
case ZERO_EXTRACT:
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr113010.c
b/gcc/testsuite/gcc.c-torture/execute/pr113010.c
new file mode 100644
index 00000000000..a95c613c1df
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr113010.c
@@ -0,0 +1,9 @@
+int minus_1 = -1;
+
+int
+main ()
+{
+ if ((0, 0xfffffffful) >= minus_1)
+ __builtin_abort ();
+ return 0;
+}
```
