This is a serious bug, since the compiler produces faulty code, without any warning! It pissed me off really bad, I had to wait a month or two to calm down and prepare a half decent bug report. It can appear anywhere and anytime. It happened with me, when I removed an unrelated line from a different portion of the code. (I know everything in the universe is related :) ) I was able to reproduce the bug in WinAVR 20080610, 20081205, 20090313 (gcc 4.3.0,4.3.2). In short the bug looks like this: TF.key32[1]=TFdw1; /// 0x04050607 484: ldi r16, 0x07 ; 7 486: mov r14, r16 488: ldi r16, 0x06 ; 6 48a: mov r15, r16 48c: ldi r16, 0x05 ; 5 48e: mov r16, r16 ;;;;;;<---- mov r16, r16 !!!! 490: ldi r16, 0x04 ; 4 ;;;;;;<---- ldi r16, 0x04 !!!! 492: mov r17, r16 494: sts 0x0064, r14 498: sts 0x0065, r15 49c: sts 0x0066, r16 4a0: sts 0x0067, r17 [...] The rest of the code is in the attached files, I tried to minimize the code, I think I left only what is needed. The working WinAVR versions (20070525 (4.1.2), 20060421 (3.4.6) ) are just that, working, (they use different temp register r17,r19,r23,r24,r25... instead of r16, it depends on the rest of the program code) but they still miss optimization. (They might still have the bug, I just was not able to find the right test case) The problem seems that register assignment and type are handled as a unit in (u)int32 instructions, rather than separate. What I mean: r0-15 no immediate instructions, need temp registers, so anytime any register of the register quad used by an int32 instruction is r0-r15 it forces all registers to be handled like no-immediate registers. what we would like is something on the line of this: ldi r16, 0x07 ; 7 mov r14, r16 ldi r16, 0x06 ; 6 mov r15, r16 ldi r16, 0x05 ; 5 ; ldi r17, 0x04 ; 4 ; instead of ldi r16, 0x04 +mov r17, r16 sts 0x0064, r14 sts 0x0065, r15 sts 0x0066, r16 sts 0x0067, r17 how any "mov r16, r16" remains in the optimized code anyway is a mystery to me :) Thank the developers hard work! compile command line: avr-gcc -v -c -mmcu=atmega16 -I. -gdwarf-2 -DF_CPU=8000000UL -DBOOTSIZE=1024 -Os -save-temps -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -fno-inline-small-functions -Wall -Winline -Wstrict-prototypes -Wa,-adhlns=vat.lst -std=gnu99 -MD -MP -MF .dep/vat.o.d vat.c -o vat.o Using built-in specs. Target: avr Configured with: ../gcc-4.3.2/configure --enable-win32-registry=WinAVR-20090313 --with-gmp=/usr/local --with-mpfr=/usr/local --prefix=/c/WinAVR --target=avr --enable-languages=c,c++,objc --with-dwarf2 --enable-doc --disable-shared --disable -libada --disable-libssp --disable-nls --with-pkgversion='WinAVR 20090313' --with-bugurl='URL:http://sourceforge.net/tracker/?atid=520074&group_id=68108&func=browse' Thread model: single gcc version 4.3.2 (WinAVR 20090313) COLLECT_GCC_OPTIONS='-v' '-c' '-mmcu=atmega16' '-I.' '-gdwarf-2' '-DF_CPU=8000000UL' '-DBOOTSIZE=1024' '-Os' '-save-temps' '-funsigned-char' '-funsigned-bitfields' '-fpack-struct' '-fshort-enums' '-fno-inline-small-functions' '-Wall' '-Winl ine' '-Wstrict-prototypes' '-std=gnu99' '-MD' '-MP' '-MF' '.dep/vat.o.d' '-o' 'vat.o' e:/winavr/20090313/bin/../libexec/gcc/avr/4.3.2/cc1.exe -E -quiet -v -I. -imultilib avr5 -iprefix e:\winavr\20090313\bin\../lib/gcc/avr/4.3.2/ -MD vat.d -MF .dep/vat.o.d -MP -MQ vat.o -DF_CPU=8000000UL -DBOOTSIZE=1024 vat.c -mmcu=atmega16 -std=gnu99 -Wall -Winline -Wstrict-prototypes -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -fno-inline-small-functions -fworking-directory -Os -fpch-preprocess -o vat.i ignoring nonexistent directory "e:/winavr/20090313/lib/gcc/../../avr/sys-include" #include "..." search starts here: #include <...> search starts here: . e:\winavr\20090313\bin\../lib/gcc/avr/4.3.2/include e:\winavr\20090313\bin\../lib/gcc/avr/4.3.2/include-fixed e:/winavr/20090313/lib/gcc/../../lib/gcc/avr/4.3.2/include e:/winavr/20090313/lib/gcc/../../lib/gcc/avr/4.3.2/include-fixed e:/winavr/20090313/lib/gcc/../../avr/include End of search list. COLLECT_GCC_OPTIONS='-v' '-c' '-mmcu=atmega16' '-I.' '-gdwarf-2' '-DF_CPU=8000000UL' '-DBOOTSIZE=1024' '-Os' '-save-temps' '-funsigned-char' '-funsigned-bitfields' '-fpack-struct' '-fshort-enums' '-fno-inline-small-functions' '-Wall' '-Winl ine' '-Wstrict-prototypes' '-std=gnu99' '-MD' '-MP' '-MF' '.dep/vat.o.d' '-o' 'vat.o' e:/winavr/20090313/bin/../libexec/gcc/avr/4.3.2/cc1.exe -fpreprocessed vat.i -quiet -dumpbase vat.c -mmcu=atmega16 -auxbase-strip vat.o -gdwarf-2 -Os -Wall -Winline -Wstrict-prototypes -std=gnu99 -version -funsigned-char -funsigned-bitfiel ds -fpack-struct -fshort-enums -fno-inline-small-functions -o vat.s GNU C (WinAVR 20090313) version 4.3.2 (avr) compiled by GNU C version 3.4.5 (mingw-vista special r3), GMP version 4.2.3, MPFR version 2.4.0. GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: abe89850c430a90419070abaa31bf632 COLLECT_GCC_OPTIONS='-v' '-c' '-mmcu=atmega16' '-I.' '-gdwarf-2' '-DF_CPU=8000000UL' '-DBOOTSIZE=1024' '-Os' '-save-temps' '-funsigned-char' '-funsigned-bitfields' '-fpack-struct' '-fshort-enums' '-fno-inline-small-functions' '-Wall' '-Winl ine' '-Wstrict-prototypes' '-std=gnu99' '-MD' '-MP' '-MF' '.dep/vat.o.d' '-o' 'vat.o' e:/winavr/20090313/bin/../lib/gcc/avr/4.3.2/../../../../avr/bin/as.exe -mmcu=atmega16 -adhlns=vat.lst -o vat.o vat.s COMPILER_PATH=e:/winavr/20090313/bin/../libexec/gcc/avr/4.3.2/;e:/winavr/20090313/bin/../libexec/gcc/;e:/winavr/20090313/bin/../lib/gcc/avr/4.3.2/../../../../avr/bin/ LIBRARY_PATH=e:/winavr/20090313/bin/../lib/gcc/avr/4.3.2/avr5/;e:/winavr/20090313/bin/../lib/gcc/avr/4.3.2/../../../../avr/lib/avr5/;e:/winavr/20090313/bin/../lib/gcc/avr/4.3.2/;e:/winavr/20090313/bin/../lib/gcc/;e:/winavr/20090313/bin/../l ib/gcc/avr/4.3.2/../../../../avr/lib/ COLLECT_GCC_OPTIONS='-v' '-c' '-mmcu=atmega16' '-I.' '-gdwarf-2' '-DF_CPU=8000000UL' '-DBOOTSIZE=1024' '-Os' '-save-temps' '-funsigned-char' '-funsigned-bitfields' '-fpack-struct' '-fshort-enums' '-fno-inline-small-functions' '-Wall' '-Winl ine' '-Wstrict-prototypes' '-std=gnu99' '-MD' '-MP' '-MF' '.dep/vat.o.d' '-o' 'vat.o'
Created attachment 17561 [details] preprocessed test case
Created attachment 17562 [details] compile environment
BYTE b[4]; *((DWORD *)b) = x; this is violating aliasing rules. Does adding -fno-strict-aliasing allow this to work?
Created attachment 17563 [details] test case source
Created attachment 17564 [details] compiled assembly lists vat_20060421.lss gcc 3.4.6 vat_20070525.lss gcc 4.1.2 vat_20080610.lss gcc 4.3.0 vat_20081205.lss gcc 4.3.2 vat_20090313.lss gcc 4.3.2
(In reply to comment #3) > BYTE b[4]; > *((DWORD *)b) = x; > this is violating aliasing rules. Does adding -fno-strict-aliasing allow this > to work? If you look at the code you can see it is never called, the only code that is actually called at all is the InitTF() assignments, the rest is just junk, that confuses the compiler. And -fno-strict-aliasing does not help, by the way the junk code works just fine, that is not the problem. Thanks anyway, I added -fno-strict-aliasing to makefile.
For convenience, here is the testcase reduced (I didn't verify it still "fails", but it obviously should). unsigned long key32[8]; void __attribute__((noinline)) InitTF(void) { key32[0]=0x00010203; key32[1]=0x04050607; key32[2]=0x08091011; key32[3]=0x12131415; key32[4]=0x00010203; key32[5]=0x04050607; key32[6]=0x08091011; key32[7]=0x12131415; } void abort (void); int main() { InitTF(); if (key32[1] != 0x04050607 || key32[5] != 0x04050607) abort (); return 0; } Can you check if that causes a runtime failure? It indeed looks like a target issue related to loading constants.
(In reply to comment #7) > For convenience, here is the testcase reduced (I didn't verify it still > "fails", but it obviously should). No it should not, the junk code is necessary to produce the error. As I said before if I remove any more lines from the code, it won't produce the bug. I suspect it's because it's massive register usage. > Can you check if that causes a runtime failure? It indeed looks like a > target issue related to loading constants. I tried your testcase, it uses r24 as a temp reg. (won't corrupt the value) I inserted the junk code into your testcase, and the bug rearreared, but only if it is inserted before InitTF. #include "junk.i.c" ///BUG unsigned long key32[8]; //#include "junk.i.c" ///BUG void __attribute__((noinline)) InitTF(void) { key32[0]=0x00010203; key32[1]=0x04050607; key32[2]=0x08091011; key32[3]=0x12131415; key32[4]=0x00010203; key32[5]=0x04050607; key32[6]=0x08091011; key32[7]=0x12131415; } //#include "junk.i.c" ///r24 void abort (void); int main() { InitTF(); if (key32[1] != 0x04050607 || key32[5] != 0x04050607) abort (); return 0; } //#include "junk.i.c" ///r24
Created attachment 17570 [details] junk code to reproduce the bug this is a reduced portion of the original program and the simplest that still generates the bug
This looks like a duplicate of bug #37466. *** This bug has been marked as a duplicate of 37466 ***