[WinAVR-users] [ winavr-Bugs-2755364 ] Wrong shift/bitfield extract in WinAVR-20090313/-20081205

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Bugs item #2755364, was opened at 2009-04-12 03:58
Message generated for change (Comment added) made by arcanum
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Category: GCC
Group: None
>Status: Closed
>Resolution: Wont Fix
Priority: 5
Private: No
Submitted By: SprinterSB (sprintersb)
Assigned to: Nobody/Anonymous (nobody)
Summary: Wrong shift/bitfield extract in WinAVR-20090313/-20081205 

Initial Comment:
The following testcase will generate wrong code compilerd as
avr-gcc -O -S foo.c

char bug (unsigned x) { return x >> 12; }

bug:
	swap r24
	andi r24,lo8(15)
	ret

both in WinAVR-20090313 and WinAVR-20081205

The same is true for >> 13, >> 14 and respective bitfield extractions.

The bug is introduced by 41-gcc-4.3.2-bug-11259_v3.patch which defines erroneous define_insn_and_split "*lshrqi3_const4", "*lshrqi3_const5", "*lshrqi3_const6".

The bug can be suppressed by -fno-split-wide-types or by disabling optimization.

For a discussion see
http://lists.gnu.org/archive/html/avr-gcc-list/2009-04/msg00005.html

Georg-Johann



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Comment By: Eric Weddington (arcanum)
Date: 2010-01-12 17:36

Message:
This needs to be reported to the GCC project at:
http://gcc.gnu.org/bugzilla/

This is not a WinAVR bug. The WinAVR User Manual states that any potential
bugs in the GCC compiler must be reported to the GCC project and not here.

Closed as "Won't Fix."

----------------------------------------------------------------------

Comment By: Anatoly Sokolov (aesok)
Date: 2009-04-18 06:35

Message:
Hi Georg-Johann.

Please, more clearly describe why you are seeing this bug.

The GCC HEAD generate this code for 'bug' function:

avr-gcc -std=gnu99 -gdwarf-2 -Wall -Os -mmcu=atmega128 -D F_CPU=4000000UL
-save-
temps    -c -o main.o main.c

.global	bug
	.type	bug, @function
bug:
.LFB0:
.LM1:
.LVL0:
/* prologue: function */
/* frame size = 0 */
.LM2:
	mov r24,r25
.LVL1:
	swap r24
	andi r24,lo8(15)
/* epilogue start */
	ret
.LFE0:
	.size	bug, .-bug


Anatoly.

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