In 2011, the rtl.texi documentation was updated to reflect that the
modes of the RTX unary operations FFS, POPCOUNT and PARITY must
match those of their operands. Unfortunately, some of the transformations
in simplify-rtx.cc predate this tightening of RTL semantics, and have
not (until now) been updated/fixed. i.e. The POPCOUNT and PARITY
optimizations were "correct" when I originally added them back in 2007.
Segher requested that I split this piece out from a fix for PR 106594 in
https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601501.html
This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32},
with no new failures. Ok for mainline?
2023-01-01 Roger Sayle <ro...@nextmovesoftware.com>
gcc/ChangeLog
* gcc/simplify-rtx.cc (simplify_unary_operation_1) <case FFS>:
Avoid generating FFS with mismatched operand and result modes, by
using an explicit SIGN_EXTEND/ZERO_EXTEND instead.
<case POPCOUNT>: Likewise, for POPCOUNT of ZERO_EXTEND.
<case PARITY>: Likewise, for PARITY of {ZERO,SIGN}_EXTEND.
Thanks in advance,
Roger
--
diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
index fc0d6c3..698ca6e 100644
--- a/gcc/simplify-rtx.cc
+++ b/gcc/simplify-rtx.cc
@@ -1404,22 +1404,32 @@ simplify_context::simplify_unary_operation_1 (rtx_code
code, machine_mode mode,
break;
case FFS:
- /* (ffs (*_extend <X>)) = (ffs <X>) */
+ /* (ffs (*_extend <X>)) = (*_extend (ffs <X>)). */
if (GET_CODE (op) == SIGN_EXTEND
|| GET_CODE (op) == ZERO_EXTEND)
- return simplify_gen_unary (FFS, mode, XEXP (op, 0),
- GET_MODE (XEXP (op, 0)));
+ {
+ temp = simplify_gen_unary (FFS, GET_MODE (XEXP (op, 0)),
+ XEXP (op, 0), GET_MODE (XEXP (op, 0)));
+ return simplify_gen_unary (GET_CODE (op), mode, temp,
+ GET_MODE (temp));
+ }
break;
case POPCOUNT:
switch (GET_CODE (op))
{
case BSWAP:
- case ZERO_EXTEND:
- /* (popcount (zero_extend <X>)) = (popcount <X>) */
+ /* (popcount (bswap <X>)) = (popcount <X>). */
return simplify_gen_unary (POPCOUNT, mode, XEXP (op, 0),
GET_MODE (XEXP (op, 0)));
+ case ZERO_EXTEND:
+ /* (popcount (zero_extend <X>)) = (zero_extend (popcount <X>)). */
+ temp = simplify_gen_unary (POPCOUNT, GET_MODE (XEXP (op, 0)),
+ XEXP (op, 0), GET_MODE (XEXP (op, 0)));
+ return simplify_gen_unary (ZERO_EXTEND, mode, temp,
+ GET_MODE (temp));
+
case ROTATE:
case ROTATERT:
/* Rotations don't affect popcount. */
@@ -1438,11 +1448,16 @@ simplify_context::simplify_unary_operation_1 (rtx_code
code, machine_mode mode,
{
case NOT:
case BSWAP:
- case ZERO_EXTEND:
- case SIGN_EXTEND:
return simplify_gen_unary (PARITY, mode, XEXP (op, 0),
GET_MODE (XEXP (op, 0)));
+ case ZERO_EXTEND:
+ case SIGN_EXTEND:
+ temp = simplify_gen_unary (PARITY, GET_MODE (XEXP (op, 0)),
+ XEXP (op, 0), GET_MODE (XEXP (op, 0)));
+ return simplify_gen_unary (GET_CODE (op), mode, temp,
+ GET_MODE (temp));
+
case ROTATE:
case ROTATERT:
/* Rotations don't affect parity. */
