From d34dbf07bdbe022cc9e96f5de2ac315ec4b20373 Mon Sep 17 00:00:00 2001 From: David Majnemer Date: Wed, 9 Sep 2015 20:20:08 +0000 Subject: Revert trunc(lshr (sext A), Cst) to ashr A, Cst This reverts commit r246997, it introduced a regression (PR24763). llvm-svn: 247180 --- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp | 20 -------------------- 1 file changed, 20 deletions(-) (limited to 'llvm/lib/Transforms') diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp index fabf80b3fd0..768616f4233 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp @@ -498,26 +498,6 @@ Instruction *InstCombiner::visitTrunc(TruncInst &CI) { return CastInst::CreateIntegerCast(Shift, CI.getType(), false); } - // Transform trunc(lshr (sext A), Cst) to ashr A, Cst to eliminate type - // conversion. - // It works because bits coming from sign extension have the same value as - // sign bit of the original value; performing ashr instead of lshr - // generates bits of the same value as the sign bit. - if (Src->hasOneUse() && - match(Src, m_LShr(m_SExt(m_Value(A)), m_ConstantInt(Cst))) && - cast(Src)->getOperand(0)->hasOneUse()) { - const unsigned ASize = A->getType()->getPrimitiveSizeInBits(); - // This optimization can be only performed when zero bits generated by - // the original lshr aren't pulled into the value after truncation, so we - // can only shift by values smaller then the size of destination type (in - // bits). - if (Cst->getValue().ult(ASize)) { - Value *Shift = Builder->CreateAShr(A, Cst->getZExtValue()); - Shift->takeName(Src); - return CastInst::CreateIntegerCast(Shift, CI.getType(), false); - } - } - // Transform "trunc (and X, cst)" -> "and (trunc X), cst" so long as the dest // type isn't non-native. if (Src->hasOneUse() && isa(Src->getType()) && -- cgit v1.2.3