[cfe-dev] [analyzer] How to walk AST template instantiations

[Ben Craig via cfe-dev]

My eventual question:

What is the best way for analysis AST visitors to visit template
instantiations?

 

Background:

I am working on a checker that will report about excessive padding.
Basically, any place where padding could be reduced by reordering data
members, I want to emit a report.  This is different from -Wpadding because
I don't want to report on items where there isn't a relatively easy fix.

 

The general way I'm implementing this is by using the
check::ASTDecl<RecordDecl> visitor, returning early for some really
troublesome cases, then using getASTRecordLayout.  I then compare the actual
size and padding against a computed optimal padding and size, and report
when the observed padding doesn't meet the optimal padding.

 

I started writing tests for this, and started to run into problems with C++
templates.  Here is the most troublesome code test case I've hit so far:

template <typename T>

struct Foo {

  // expected-warning at +1{{Excessive padding in struct 'Foo<int>::Nested'}}

  struct Nested { // doesn't actually warn though.

    char c1;

    T t;

    char c2;

  };

};

 

struct Holder { //no-warning

  Foo<int>::Nested t1;

  Foo<char>::Nested t2;

};

 

It seems that by default, AnalysisConsumer doesn't visit template
instantiations.  In fact, if I add "bool shouldVisitTemplateInstantiations()
const { return true; }" to the AnalysisConsumer class, I get the reports I
expect.  Is there a better way for me to accomplish my goal?  I don't like
the idea of turning on instantiation visitation for every checker just
because my checker needs it.

 

Before I found AnalysisConsumer, I did make an attempt to walk the
instantiations by visiting ClassTemplateDecl and iterating over
specializations.  That works ok if I don't have nested Records, like I
posted above.  I hadn't found the "right" way to recurse into the structure
before finding shouldVisitTemplateInsantiations.  Maybe a "better" approach
is to basically copy RecursiveASTVisitor::TraverseClassInstantiation?  I'm
not sure if I'm comfortable duplicating that code, but if it's the better
option then I will.

 

Thanks for the help,

Ben Craig

 

Employee of Qualcomm Innovation Center, Inc.

Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
Foundation Collaborative Project

 

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