From 6134fbccefd5c4e8ca0f592d0487ea213b864c0d Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Wed, 13 Aug 2008 23:12:35 +0000 Subject: Fix a bogus srem rule - a negative value srem'd by a power-of-2 can have a non-negative result; for example, -16%16 is 0. Also, clarify the related comments. This fixes PR2670. llvm-svn: 54767 --- llvm/lib/Analysis/ValueTracking.cpp | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) (limited to 'llvm/lib/Analysis/ValueTracking.cpp') diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index e35f0d0fced..3a04f5eb869 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -369,15 +369,13 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, Depth+1); - // The sign of a remainder is equal to the sign of the first - // operand (zero being positive). + // If the sign bit of the first operand is zero, the sign bit of + // the result is zero. If the first operand has no one bits below + // the second operand's single 1 bit, its sign will be zero. if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits)) KnownZero2 |= ~LowBits; - else if (KnownOne2[BitWidth-1]) - KnownOne2 |= ~LowBits; KnownZero |= KnownZero2 & Mask; - KnownOne |= KnownOne2 & Mask; assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); } -- cgit v1.2.3