http://llvm.org/bugs/show_bug.cgi?id=20301
Bug ID: 20301
Summary: implicit _Noreturn
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Static Analyzer
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
I have compiled llvam/clang based on today's trunk.
When I compile this program
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
static void z() {
exit(0);
}
int main(__attribute__((unused)) int argc, char** argv) {
int a;
if (strlen(argv[1]) < 3 || sscanf(argv[1], "%i", &a) < 1)
z();
if (a > 0) printf("A");
}
with
clang -std=c11 -Weverything unitialized-noreturn.c 2> unitialized-error
I get
unitialized-noreturn.c:5:17: warning: function 'z' could be declared with
attribute 'noreturn' [-Wmissing-noreturn]
static void z() {
^
unitialized-noreturn.c:11:7: warning: variable 'a' is used uninitialized
whenever '||' condition is true [-Wsometimes-uninitialized]
if (strlen(argv[1]) < 3 || sscanf(argv[1], "%i", &a) < 1)
^~~~~~~~~~~~~~~~~~~
unitialized-noreturn.c:13:7: note: uninitialized use occurs here
if (a > 0) printf("A");
^
unitialized-noreturn.c:11:7: note: remove the '||' if its condition is always
false
if (strlen(argv[1]) < 3 || sscanf(argv[1], "%i", &a) < 1)
^~~~~~~~~~~~~~~~~~~~~~
unitialized-noreturn.c:10:8: note: initialize the variable 'a' to silence this
warning
int a;
^
= 0
2 warnings generated.
However, when I put _Noreturn on line 5, right before the definition of
function z() I get no warnings and no notes.
Provided that clang correctly detects the noreturn-nature of z(), why isn't
_Noreturn implied, but has to be provided explicitly? I see _Noreturn as a way
to hint the compiler (e.g. in (forward) declaration) that a function does not
return, which only necessary when the compiler cannot determine this on its
own.
Why does the second note ("||") depend on _Noreturn?
I expect that clang puts implicit _Noreturn to z() and that the ||-note does
not depend on _Noreturn.
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