http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59609
Bug ID: 59609 Summary: LRA generates bad code for libgcc function udivmoddi4 on thumb1 target Product: gcc Version: unknown Status: UNCONFIRMED Severity: blocker Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: terry.guo at arm dot com Created attachment 31523 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31523&action=edit a reduced case Thumb-1 target like cortex-m0 hasn't hardware div instruction, thus the function __udivmoddi4 in libgcc is used. However this function is wrongly compiled by LRA which is enabled in recent gcc, codes that use __udivmoddi4 will get a wrong results. When print unsigned long long value using printf function, the printf function will use __udivmoddi4 and eventually will end up with dead loop. Attachment is a reduced case based on __udivmoddi4 function.And I am using the latest gcc trunk code. Compile the attached case with command: arm-none-eabi-gcc -mthumb -mcpu=cortex-m0 -O2 -S myudi.c then check the assembly code: sub r3, r3, #32 << should initialize ip after this insn bpl .LCB31 b .L4 @long jump .LCB31: mov ip, r3 mov r3, r9 mov r2, ip lsl r3, r3, r2 mov r7, r3 .L5: mov r3, r9 lsl r3, r3, r1 mov r6, r3 cmp r7, r5 bhi .L20 beq .L29 .L22: mov r3, ip << Here is the wrong code, the ip is uninitialized. sub r4, r4, r6 sbc r5, r5, r7 cmp r3, #0 bge .LCB50