From 5ea4fc0b33d12c51cc55297747057c00942db662 Mon Sep 17 00:00:00 2001 From: David Majnemer Date: Mon, 14 Jul 2014 19:49:57 +0000 Subject: 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 --- llvm/lib/Analysis/InstructionSimplify.cpp | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'llvm/lib/Analysis') diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp index bd42af15da3..1054c7935b5 100644 --- a/llvm/lib/Analysis/InstructionSimplify.cpp +++ b/llvm/lib/Analysis/InstructionSimplify.cpp @@ -1964,7 +1964,15 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS, 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]. -- cgit v1.2.3