I have been adding rotate capability to AVR port and have come this bug in
optabs.c: expand_binop()
This occurs during a rotate expansion. For example
target = op0 rotated by op1
In the particular situation (code extract below) it tries a reverse rotate of
(bits - op1). Where this expression is then expanded into an integer,
a negation or subtraction depending on type of op1 and target.
The expansion of the subtraction is using the mode of the target - it should be
using the mode of op1.
The mode of the rotation amount need not be the same as the target.
target:DI = Op0:DI rotate op1:HI
In my testcase it is not and I get asserts latter in simplfy_rtx with the
mismatched inner/outer modes.
The negation mode looks equally wrong.
I found this on testcase 20010226-1.c with gcc 4.42 (line 55) - however, it
would appear to be on 4.5 and perhaps earlier versions.
Revision 126370 added this particular code to optabs.c in July 2007
/* If we were trying to rotate, and that didn't work, try rotating
the other direction before falling back to shifts and bitwise-or. */
if (((binoptab == rotl_optab
&& optab_handler (rotr_optab, mode)->insn_code != CODE_FOR_nothing)
|| (binoptab == rotr_optab
&& optab_handler (rotl_optab, mode)->insn_code != CODE_FOR_nothing))
&& mclass == MODE_INT)
{
optab otheroptab = (binoptab == rotl_optab ? rotr_optab : rotl_optab);
rtx newop1;
unsigned int bits = GET_MODE_BITSIZE (mode);
if (CONST_INT_P (op1))
newop1 = GEN_INT (bits - INTVAL (op1));
else if (targetm.shift_truncation_mask (mode) == bits - 1)
newop1 = negate_rtx (mode, op1);
else
newop1 = expand_binop (mode, sub_optab,
GEN_INT (bits), op1,
NULL_RTX, unsignedp, OPTAB_DIRECT);
--
Summary: optabs expands rotate using wrong mode
Product: gcc
Version: 4.4.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: hutchinsonandy at gcc dot gnu dot org
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: avr-unknown-none
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41738
