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Add backtrace to valueflow in debug mode #4195

Merged
merged 9 commits into from
Jun 12, 2022
Merged

Add backtrace to valueflow in debug mode #4195

merged 9 commits into from
Jun 12, 2022

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pfultz2
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@pfultz2 pfultz2 commented Jun 10, 2022

When using debug_valueflow this will now print out the backtrace where value was set or forwarded from.

This relies on std::source_location which is a C++20 feature. However, if std::experimental::source_location(usually require c++14) is available, then it will use that. If not, it uses a fallback with an empty source location.

I also update the CMAKE_CXX_STANDARD variable to make it a cache variable so it can be switched to C++14 without changing the source, since at least C++14 is needed.

It is possible to enable support on newer clang or gcc with just C++11 using intrinsics, but I think this is simpler for now.

The backtrace is appended to the regular path and looks something like this:

test.cpp:17:33: debug: The value is always !-1 [valueFlow]
    if (debug_valueflow(std::min(apple, banana)) != -1) {
                                ^
test.cpp:14:15: note: Assuming that condition 'fruit==-1' is not redundant
    if (fruit == -1) {
              ^
test.cpp:11:16: note: banana is assigned 'bananas.empty()?-1:bananas.front()' here.
    int banana = bananas.empty() ? -1 : bananas.front();
               ^
test.cpp:13:15: note: fruit is assigned 'std::max(apple,banana)' here.
    int fruit = std::max(apple, banana);
              ^
test.cpp:14:15: note: Assuming condition is false
    if (fruit == -1) {
              ^
test.cpp:11:16: note: banana is assigned 'bananas.empty()?-1:bananas.front()' here.
    int banana = bananas.empty() ? -1 : bananas.front();
               ^
test.cpp:14:15: note: Assuming condition is false
    if (fruit == -1) {
              ^
test.cpp:14:19: note: valueflow.cpp:1154: valueFlowSetConstantValue => setTokenValue: always -1
    if (fruit == -1) {
                  ^
test.cpp:17:5: note: valueflow.cpp:6100: operator() => valueFlowForward: always !-1
    if (debug_valueflow(std::min(apple, banana)) != -1) {
    ^
test.cpp:17:33: note: valueflow.cpp:2809: update => setTokenValue: always !-1
    if (debug_valueflow(std::min(apple, banana)) != -1) {
                                ^
test.cpp:17:33: note: The value is always !-1
    if (debug_valueflow(std::min(apple, banana)) != -1) {
                                ^

@pfultz2
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pfultz2 commented Jun 11, 2022

@danmar any feedback?

danmar
danmar approved these changes Jun 12, 2022
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@danmar danmar left a comment

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if it will help you it's good.

@danmar danmar merged commit cee48e5 into danmar:main Jun 12, 2022
@pfultz2 pfultz2 deleted the valueflow-debug-backtrace branch June 12, 2022 11:39
@chrchr-github chrchr-github mentioned this pull request Jun 14, 2022
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@danmar danmar danmar approved these changes

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