https://bugs.llvm.org/show_bug.cgi?id=41815
Bug ID: 41815
Summary: Value tracking of undefined to remove branches.
Product: new-bugs
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: sland...@gmail.com
CC: htmldevelo...@gmail.com, llvm-bugs@lists.llvm.org
The following code does not need a branch, because uninitialized memory has
undefined contents, and certainly shouldn't have one when the popcnt
instruction is supported:
struct get_sparse_ret {
size_t index;
bool godefault;
};
struct get_sparse_ret
__getsparse(size_t key, struct sparse_table_entry *map) {
struct get_sparse_ret ret;
if ((((key * 64) / 64) * 64) * 16 > map[0].length) {
ret.godefault = true;
return ret;
}
ret = __getsparseinbounds(key, map);
return ret;
}
I could put the if after the function call, but that wouldn't specify that I
don't care about the first return value if the second return value is true (and
C doesn't have an undefined I can set it to to communicate that).
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