hohn/codeql
1
0
Fork 0
mirror of https://github.com/github/codeql.git synced 2026-04-28 10:15:14 +02:00
Code Issues Packages Projects Releases Wiki Activity

C++: Simplify automaticVariableAddressEscapes

Browse Source 
The `automaticVariableAddressEscapes` predicate got join-ordered badly
in its `unaliased_ssa` version. These are the tuple counts on Wireshark,
where one pipeline step is seen to have 716 million tuples:

```
[2019-03-02 11:29:41] (42s) Starting to evaluate predicate AliasAnalysis::automaticVariableAddressEscapes#2#f
[2019-03-02 11:30:06] (67s) Tuple counts:
                      353419    ~0%      {1} r1 = JOIN project#Instruction::VariableAddressInstruction#class#2#ff WITH AliasAnalysis::resultEscapesNonReturn#2#f ON project#Instruction::VariableAddressInstruction#class#2#ff.<0>=AliasAnalysis::resultEscapesNonReturn#2#f.<0> OUTPUT FIELDS {AliasAnalysis::resultEscapesNonReturn#2#f.<0>}
                      353419    ~0%      {2} r2 = JOIN r1 WITH IRConstruction::Cached::getInstructionEnclosingFunctionIR#ff@staged_ext ON r1.<0>=IRConstruction::Cached::getInstructionEnclosingFunctionIR#ff@staged_ext.<0> OUTPUT FIELDS {IRConstruction::Cached::getInstructionEnclosingFunctionIR#ff@staged_ext.<1>,r1.<0>}
                      353419    ~0%      {2} r3 = JOIN r2 WITH FunctionIR::FunctionIR::getFunction_dispred#3#ff ON r2.<0>=FunctionIR::FunctionIR::getFunction_dispred#3#ff.<0> OUTPUT FIELDS {FunctionIR::FunctionIR::getFunction_dispred#3#ff.<1>,r2.<1>}
                      716040298 ~0%      {2} r4 = JOIN r3 WITH IRVariable::IRVariable#class#3#ff_10#join_rhs ON r3.<0>=IRVariable::IRVariable#class#3#ff_10#join_rhs.<0> OUTPUT FIELDS {IRVariable::IRVariable#class#3#ff_10#join_rhs.<1>,r3.<1>}
                      4480139   ~0%      {2} r5 = JOIN r4 WITH IRVariable::IRAutomaticVariable#class#3#ff ON r4.<0>=IRVariable::IRAutomaticVariable#class#3#ff.<0> OUTPUT FIELDS {r4.<1>,r4.<0>}
                      66760     ~91%     {1} r6 = JOIN r5 WITH Instruction::VariableInstruction::getVariable_dispred#2#ff ON r5.<0>=Instruction::VariableInstruction::getVariable_dispred#2#ff.<0> AND r5.<1>=Instruction::VariableInstruction::getVariable_dispred#2#ff.<1> OUTPUT FIELDS {r5.<1>}
                                         return r6
[2019-03-02 11:30:06] (67s)  >>> Relation AliasAnalysis::automaticVariableAddressEscapes#2#f: 35531 rows using 0 MB
```

The predicate contained a cyclic join, which is always hard to optimize.
I couldn't see a reason to join the `FunctionIR`, so I removed that
part. The predicate is now fast, and there are no changes in the tests.
This commit is contained in:
Jonas Jensen
2019-03-02 12:07:04 +01:00
committed by Robert Marsh
parent a72cd23d1d
commit 794a8954cd
2 changed files with 10 additions and 18 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/AliasAnalysis.qll
View File

@@ -248,15 +248,11 @@ predicate resultEscapesNonReturn(Instruction instr) {
* domain of the analysis.
*/
private predicate automaticVariableAddressEscapes(IRAutomaticVariable var) {
exists(FunctionIR funcIR |
funcIR = var.getEnclosingFunctionIR() and
// The variable's address escapes if the result of any
// VariableAddressInstruction that computes the variable's address escapes.
exists(VariableAddressInstruction instr |
instr.getEnclosingFunctionIR() = funcIR and
instr.getVariable() = var and
resultEscapesNonReturn(instr)
)
// The variable's address escapes if the result of any
// VariableAddressInstruction that computes the variable's address escapes.
exists(VariableAddressInstruction instr |
instr.getVariable() = var and
resultEscapesNonReturn(instr)
)
}

14
cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/AliasAnalysis.qll
View File

@@ -248,15 +248,11 @@ predicate resultEscapesNonReturn(Instruction instr) {
* domain of the analysis.
*/
private predicate automaticVariableAddressEscapes(IRAutomaticVariable var) {
exists(FunctionIR funcIR |
funcIR = var.getEnclosingFunctionIR() and
// The variable's address escapes if the result of any
// VariableAddressInstruction that computes the variable's address escapes.
exists(VariableAddressInstruction instr |
instr.getEnclosingFunctionIR() = funcIR and
instr.getVariable() = var and
resultEscapesNonReturn(instr)
)
// The variable's address escapes if the result of any
// VariableAddressInstruction that computes the variable's address escapes.
exists(VariableAddressInstruction instr |
instr.getVariable() = var and
resultEscapesNonReturn(instr)
)
}