[cfe-dev] -ftrapv flag leads to compilation error

[peng li]

Hi there

First I used command "clang -o add add.c -ftrapv" to compile the add.c 
which implements two signed integers add operation leading to overflow. 
But clang can not compile successfully. The concrete error
message is pasted as follows:

/tmp/cc-oMjvJr.o: In function `main':
add.c:(.text+0x3b): undefined reference to `__overflow_handler'
collect2: ld returned 1 exit status
clang: error: linker command failed with exit code 1 (use -v to see 
invocation)


Then I also extended the command to "clang -o add add.c -ftrapv -S 
-emit-llvm" and found the dynamic checks have been expressed and 
instrumented into the corresponding LLVM code. I think those checks, 
such as "overflow", "overflow.continue" should also be considered as the 
dynamic undefined behavior checks, correct?? Since resorting to those 
checks, clang will not dump the warnings at compile time.


Regards


Peng