Inverse expression IR for casts is sometime incorrect

[dtarditi]

While doing the upgrade to clang 17 sources, I found that a compiler assert was failing in a new test that was added to clang-17: test/Sema/pointer-subtraction.c.

 #3 0x00007ff67d2383dd llvm::llvm_unreachable_internal(char const *, char const *, unsigned int) ... llvm\lib\Support\ErrorHandling.cpp:212:0
 #4 0x00007ff6861abd97 `anonymous namespace'::IntExprEvaluator::VisitCastExpr ... clang\lib\AST\ExprConstant.cpp:13583:0

A minimal cut-down case is:

void a(void) {
  char *f = (char *)0;
  
    f = (char *)((char *)0 - f);         // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}};
    f = (char *)((char *)0 - f);         // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
}

I tracked the assert failure to incorrect IR being created for inverse expressions for casts in lib/AST/ExprUtils.cpp in the InverseUtil class. The problem is that some cast operators need to be inverted too. For example CK_IntegralToPointer needs to be inverted to CK_PointerToIntegral.