[flang-commits] [flang] [flang] Add ETIME runtime and lowering intrinsics implementation (PR #90578)

[jiajie zhang via flang-commits]

================
@@ -916,3 +916,54 @@ used in constant expressions have currently no folding support at all.
   - If a condition occurs that would assign a nonzero value to `CMDSTAT` but the `CMDSTAT` variable is not present, error termination is initiated.
     - On POSIX-compatible systems, the child process (async process) will be terminated with no effect on the parent process (continues).
     - On Windows, error termination is not initiated.
+
+### Non-Standard Intrinsics: ETIME
+
+#### Description
+`ETIME(VALUES, TIME)` returns the number of seconds of runtime since the start of the process’s execution in *TIME*. *VALUES* returns the user and system components of this time in `VALUES(1)` and `VALUES(2)` respectively. *TIME* is equal to `VALUES(1) + VALUES(2)`.
+
+On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wrap around) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.
+
+This intrinsic is provided in subroutine forms only.
+
+*VALUES* and *TIME* are `INTENT(OUT)` and provide the following:
+
+
+|               |                                   |
+|---------------|-----------------------------------|
+| `VALUES(1)`   | User time in seconds.             |
+| `VALUES(2)`   | System time in seconds.           |
+| `TIME`        | Run time since start in seconds.  |
+
+#### Usage and Info
+
+- **Standard:** GNU extension
+- **Class:** Subroutine
+- **Syntax:** `CALL ETIME(VALUES, TIME)`
+- **Arguments:**
+
+| Argument   | Description                                                           |
+|------------|-----------------------------------------------------------------------|
+| `VALUES`   | The type shall be REAL(4), DIMENSION(2).                              |
+| `TIME`     | The type shall be REAL(4).                                            |
+
+#### Example
----------------
JumpMasterJJ wrote:

Ok, I will add the reference.

https://github.com/llvm/llvm-project/pull/90578