On Tue, Jul 7, 2015 at 8:35 PM, Uros Bizjak <ubiz...@gmail.com> wrote:
> BT has *slightly* higher latency than TEST (0.33 vs. 0.25 cycles on a
> modern processor), so I have limited the conversion to -Os in case the
> bit-test is in the low 32 bits.
A small update, in case of -Os, unpatched compiler generates andb for
0 <= n <= 7 with:
0: 83 e7 20 and $0x20,%edi
vs.
0: 0f ba e7 05 bt $0x5,%edi
Attached patch updated the splitter condition to reflect the above.
2015-07-08 Uros Bizjak <ubiz...@gmail.com>
* config/i386/i386.md (*jcc_bt<mode>): Only allow const_int values
more than or equal 8 and less than 32 when optimizing for size.
Tested on x86_64-linux-gnu {,-m32} and committed to mainline SVN.
Uros.
Index: config/i386/i386.md
===================================================================
--- config/i386/i386.md (revision 225533)
+++ config/i386/i386.md (working copy)
@@ -10811,7 +10811,7 @@
&& (CONST_INT_P (operands[2])
? (INTVAL (operands[2]) < GET_MODE_BITSIZE (<MODE>mode)
&& INTVAL (operands[2])
- >= (optimize_function_for_size_p (cfun) ? 0 : 32))
+ >= (optimize_function_for_size_p (cfun) ? 8 : 32))
: register_operand (operands[2], SImode))
&& can_create_pseudo_p ()"
"#"
