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Remove dead code in instcombine.

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Don't replace shifts greater than the type with the maximum shift.

This isn't hit anywhere in the tests, and somewhere else is replacing
these with undef.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207000 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matt Arsenault 2014-04-23 16:48:40 +00:00
parent d5a7c3f2ec
commit e0f15f8b7a
1 changed files with 2 additions and 11 deletions
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13
lib/Transforms/InstCombine/InstCombineShifts.cpp
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@ -337,21 +337,12 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
GetShiftedValue(Op0, COp1->getZExtValue(), isLeftShift, *this));
}
// See if we can simplify any instructions used by the instruction whose sole
// purpose is to compute bits we don't care about.
uint32_t TypeBits = Op0->getType()->getScalarSizeInBits();
// shl i32 X, 32 = 0 and srl i8 Y, 9 = 0, ... just don't eliminate
// a signed shift.
//
if (COp1->uge(TypeBits)) {
if (I.getOpcode() != Instruction::AShr)
return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
// ashr i32 X, 32 --> ashr i32 X, 31
I.setOperand(1, ConstantInt::get(I.getType(), TypeBits-1));
return &I;
}
assert(!COp1->uge(TypeBits) &&
"Shift over the type width should have been removed already");
// ((X*C1) << C2) == (X * (C1 << C2))
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0))