InstSimplify: The upper bound of X / C was missing a rounding step
Summary:
When calculating the upper bound of X / -8589934592, we would perform
the following calculation: Floor[INT_MAX / 8589934592]
However, flooring the result would make us wrongly come to the
conclusion that 1073741824 was not in the set of possible values.
Instead, use the ceiling of the result.
Reviewers: nicholas
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D4502
llvm-svn: 212976
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index bd42af1..1054c79 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1964,7 +1964,15 @@
APInt Val = CI2->getValue().abs();
if (!Val.isMinValue()) {
Lower = IntMin.sdiv(Val);
- Upper = IntMax.sdiv(Val) + 1;
+ APInt Rem;
+ APInt::sdivrem(IntMax, Val, Upper, Rem);
+ // We may need to round the result of the INT_MAX / CI2 calculation up
+ // if we see that the division was not exact.
+ if (Rem.isMinValue())
+ Upper = Upper + 1;
+ else
+ Upper = Upper + 2;
+ assert(Upper != Lower && "Upper part of range has wrapped!");
}
} else if (match(LHS, m_LShr(m_Value(), m_ConstantInt(CI2)))) {
// 'lshr x, CI2' produces [0, UINT_MAX >> CI2].