Hi, I am trying to track down/fix PR target/45291. The problem is that
pass .subreg1 generates invalid subregs.
According to internals "10.8 Registers and Memory, Normal Subregs"
a normal (non-paradoxical) subreg as Lvalue sets the specifyed subreg
and leaves the remaining part of the target word undefined. This
happens in the following test case
unsigned char func1(void);
void funct2(int l);
void dummy(void)
{
int l = 256 * func1() + func1();
if (l > 256)
return;
func1();
funct2(l);
}
compiled with
avr-gcc -S pr45291.c -O2 -mmcu=atmega8 -dP -da -v
Using built-in specs.
COLLECT_GCC=/home/georg/gcc/install/gcc-4.5/bin/avr-gcc
COLLECT_LTO_WRAPPER=/mnt/nfs/home/georg/gcc/install/gcc-4.5/bin/../libexec/gcc/avr/4.5.3/lto-wrapper
Target: avr
Configured with:
/gnu/source/gcc.gnu.org/branches/gcc-4_5-branch/configure --target=avr
--prefix=/home/georg/gcc/install/gcc-4.5 --enable-languages=c,c++
--disable-libssp --disable-libada --disable-nls --disable-shared
Thread model: single
gcc version 4.5.3 20110223 (prerelease) (GCC)
COLLECT_GCC_OPTIONS='-O2' '-S' '-mmcu=atmega8' '-dP' '-da' '-v'
/mnt/nfs/home/georg/gcc/install/gcc-4.5/bin/../libexec/gcc/avr/4.5.3/cc1
-quiet -v -imultilib avr4 -iprefix
/mnt/nfs/home/georg/gcc/install/gcc-4.5/bin/../lib/gcc/avr/4.5.3/
pr45291.c -quiet -dumpbase pr45291.c -dP -da -mmcu=atmega8 -auxbase
pr45291 -O2 -version -o pr45291.s
GNU C (GCC) version 4.5.3 20110223 (prerelease) (avr)
compiled by GNU C version 4.3.2 [gcc-4_3-branch revision
141291], GMP version 4.3.1, MPFR version 2.4.2, MPC version 0.8.1
[...]
COLLECT_GCC_OPTIONS='-O2' '-S' '-mmcu=atmega8' '-dP' '-da' '-v'
======================
In pass .148r.jump everything looks fine:
(note 2 3 6 2 NOTE_INSN_FUNCTION_BEG)
(call_insn 6 2 7 2 pr45291.c:6 (set (reg:QI 24 r24)
(call (mem:HI (symbol_ref:HI ("func1") [flags 0x41]
<function_decl 0xb76a5700 func1>) [0 S2 A8])
(const_int 0 [0x0]))) 123 {call_value_insn} (nil)
(nil))
(insn 7 6 9 2 pr45291.c:6 (set (reg:QI 41 [ D.1925 ])
(reg:QI 24 r24)) 4 {*movqi} (nil))
(call_insn 9 7 10 2 pr45291.c:6 (set (reg:QI 24 r24)
(call (mem:HI (symbol_ref:HI ("func1") [flags 0x41]
<function_decl 0xb76a5700 func1>) [0 S2 A8])
(const_int 0 [0x0]))) 123 {call_value_insn} (nil)
(nil))
(insn 10 9 11 2 pr45291.c:6 (set (reg:QI 44 [ D.1928 ])
(reg:QI 24 r24)) 4 {*movqi} (nil))
(insn 11 10 12 2 pr45291.c:6 (set (reg:HI 49)
(zero_extend:HI (reg:QI 41 [ D.1925 ]))) 94 {zero_extendqihi2}
(nil))
(insn 12 11 13 2 pr45291.c:6 (set (reg:HI 50)
(ashift:HI (reg:HI 49)
(const_int 8 [0x8]))) 68 {ashlhi3} (nil))
(insn 13 12 14 2 pr45291.c:6 (set (reg:HI 51)
(zero_extend:HI (reg:QI 44 [ D.1928 ]))) 94 {zero_extendqihi2}
(nil))
(insn 14 13 15 2 pr45291.c:6 (set (reg/v:HI 46 [ l ])
(plus:HI (reg:HI 50)
(reg:HI 51))) 22 {*addhi3} (nil))
Then .149r.subreg1 generates insns 33 and 34 with insn 34 nullifying
insn 33.
(note 2 3 6 2 NOTE_INSN_FUNCTION_BEG)
(call_insn 6 2 7 2 pr45291.c:6 (set (reg:QI 24 r24)
(call (mem:HI (symbol_ref:HI ("func1") [flags 0x41]
<function_decl 0xb76c6700 func1>) [0 S2 A8])
(const_int 0 [0x0]))) 123 {call_value_insn} (nil)
(nil))
(insn 7 6 9 2 pr45291.c:6 (set (reg:QI 41 [ D.1925 ])
(reg:QI 24 r24)) 4 {*movqi} (nil))
(call_insn 9 7 10 2 pr45291.c:6 (set (reg:QI 24 r24)
(call (mem:HI (symbol_ref:HI ("func1") [flags 0x41]
<function_decl 0xb76c6700 func1>) [0 S2 A8])
(const_int 0 [0x0]))) 123 {call_value_insn} (nil)
(nil))
(insn 10 9 31 2 pr45291.c:6 (set (reg:QI 44 [ D.1928 ])
(reg:QI 24 r24)) 4 {*movqi} (nil))
(insn 31 10 32 2 pr45291.c:6 (set (reg:QI 54)
(reg:QI 41 [ D.1925 ])) 4 {*movqi} (nil))
(insn 32 31 33 2 pr45291.c:6 (set (reg:QI 55 [+1 ])
(const_int 0 [0x0])) 4 {*movqi} (nil))
(insn 33 32 34 2 pr45291.c:6 (set (subreg:QI (reg:HI 50) 1)
(reg:QI 54)) 4 {*movqi} (nil))
(insn 34 33 13 2 pr45291.c:6 (set (subreg:QI (reg:HI 50) 0)
(const_int 0 [0x0])) 4 {*movqi} (nil))
(insn 13 34 14 2 pr45291.c:6 (set (reg:HI 51)
(zero_extend:HI (reg:QI 44 [ D.1928 ]))) 94 {zero_extendqihi2}
(nil))
(insn 14 13 15 2 pr45291.c:6 (set (reg/v:HI 46 [ l ])
(plus:HI (reg:HI 50)
(reg:HI 51))) 22 {*addhi3} (nil))
Insn 33 survives until .188r.ira and is kicked out there. So despite
my comment in the original bug report where I suspected avr backend to
emit the bad subregs, it is actually a middle-end bug, right?
Target avr suffers from similar problems in 4.3, 4.4 and 4.6 which are
all reported against avr backend, not against middleend/rtl optimizers.
PR46779 shows the bug for avr-gcc-4.4.6 (prerelease)
Thanks, Johann
