[clang++]: Incorrect warning emited for [-Wfor-loop-analysis]

[greg7mdp]

Warning correctly states that the variables are not modified in the loop body, but height is incremented nevertheless (in the incr_height lambda) and the loop is fine.

See example program:

// compile with `clang++-20 -std=c++20 -Wall -c loop.cpp`
//
// ~/tmp ❯ clang++-20 -std=c++20 -Wall -c loop.cpp
// loop.cpp:10:35: warning: variables 'height' and 'end_height' used in loop condition not modified in loop body [-Wfor-loop-analysis]
//    10 |    for (uint32_t end_height = 27; height <= end_height; incr_height())
//       |                                   ^~~~~~    ~~~~~~~~~~
// 1 warning generated.
// -----------------------------------------------------------------------------------------------------------------------------------
#include <cstdint>

extern void add_to_expected_table(uint32_t h);

void test() {
   uint32_t height = 0;

   auto incr_height = [&height]() { ++height; };

   for (uint32_t end_height = 27; height <= end_height; incr_height())
      add_to_expected_table(height);
}

[shafik]

https://godbolt.org/z/5Ke83zs51

[shafik]

It looks like this is handled in CheckForLoopConditionalStatement:

llvm-project/clang/lib/Sema/SemaStmt.cpp

Line 2018 in 0668bb2

void CheckForLoopConditionalStatement(Sema &S, Expr *Second,

I think maybe the call to DeclMather for the Body here:

llvm-project/clang/lib/Sema/SemaStmt.cpp

Line 2046 in 0668bb2

DeclMatcher(S, Decls, Body).FoundDeclInUse())

Is the important part, it looks like does not handle CallExpr:

llvm-project/clang/lib/Sema/SemaStmt.cpp

Line 1939 in 0668bb2

class DeclMatcher : public EvaluatedExprVisitor<DeclMatcher> {

but I could be off