https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67979
Bug ID: 67979
Summary: dead code elimination deleted the predicated branch
within the function block.
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: feqin1023 at gmail dot com
Target Milestone: ---
Created attachment 36518
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36518&action=edit
the source test dead code elimination.
if i have this input:
/*--------------------test.c----------------------------*/
void bar_i(int);
void foo(int *x) {
int y = *x; // dead code can be clean
if (!x)
return; // this branch ALSO will be clean
bar_i(y);
}
/*------------------------------------------------------*/
we call gcc like this:
gcc -O2 -S test.c
the the whole branch in function foo(int *) will be clean.
BUT, if foo(int *) is called like this:
foo(NULL);
gcc has CHANGED the original semantic even sometimes which
is error. but compiler can do this?
I also test Clang, Clang ALWAYS keep the branch in foo(int *).
