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C++: Simple constant analysis

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This change moves the simple constant analysis that was used by the const_func test into a pyrameterized module for use on any stage of the IR. This will be used to detect unreachable code.
This commit is contained in:
Dave Bartolomeo
2018-12-07 10:40:16 -08:00
parent 6a11ef5c18
commit 59fc77f066
11 changed files with 143 additions and 22 deletions
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23
cpp/ql/test/library-tests/ir/constant_func/constant_func.ql
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@@ -1,29 +1,8 @@
import default
import semmle.code.cpp.ir.IR
import semmle.code.cpp.ir.implementation.aliased_ssa.constant.ConstantAnalysis
import semmle.code.cpp.ir.internal.IntegerConstant
language[monotonicAggregates]
IntValue getConstantValue(Instruction instr) {
result = instr.(IntegerConstantInstruction).getValue().toInt() or
exists(BinaryInstruction binInstr, IntValue left, IntValue right |
binInstr = instr and
left = getConstantValue(binInstr.getLeftOperand()) and
right = getConstantValue(binInstr.getRightOperand()) and
(
binInstr instanceof AddInstruction and result = add(left, right) or
binInstr instanceof SubInstruction and result = sub(left, right) or
binInstr instanceof MulInstruction and result = mul(left, right) or
binInstr instanceof DivInstruction and result = div(left, right)
)
) or
result = getConstantValue(instr.(CopyInstruction).getSourceValue()) or
exists(PhiInstruction phi |
phi = instr and
result = max(PhiOperand operand | operand = phi.getAnOperand() | getConstantValue(operand.getDefinitionInstruction())) and
result = min(PhiOperand operand | operand = phi.getAnOperand() | getConstantValue(operand.getDefinitionInstruction()))
)
}
from FunctionIR funcIR, int value
where
value = getValue(getConstantValue(funcIR.getReturnInstruction().(ReturnValueInstruction).getReturnValue()))