https://bugs.llvm.org/show_bug.cgi?id=47973
Bug ID: 47973
Summary: Undefined behavior in int division with INT_MIN param
Product: compiler-rt
Version: 11.0
Hardware: All
OS: All
Status: NEW
Severity: normal
Priority: P
Component: builtins
Assignee: unassignedb...@nondot.org
Reporter: aysheku...@gmail.com
CC: llvm-bugs@lists.llvm.org
In the implementation for software integer division a/b (and mod a%b) in
int_div_impl.inc, the absolute values of a and b are calculated like so:
a = (a ^ s_a) - s_a;
(The variable s_a is -1 or 0 depending on the signedness of a.)
In the case where a (or b) is INT_MIN, this can mean that we calculate INT_MAX
+ 1 in signed integer operations. Calculating these as unsigned integers would
avoid this undefined behaviour.
In a similar fashion, the return statement can result in unsigned underflow
because it substracts s_a which gets promoted to unsigned UINT_MAX due to the
COMPUTE_UDIV being unsigned. Rewriting it as + (-s_a) would remove the
undefined behaviour.
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