[Lldb-commits] [PATCH] D126359: [LLDB] Add basic floating point ops to IR interpreter

[Greg Clayton via Phabricator via lldb-commits]

clayborg added a comment.

Will the floating point emulation be perfect compared to actually JITing the code? If we are going to enable this feature I would like to see tests that actually JIT code do the same operations somehow to verify that things match up with the IR interpreted results produce. The main reason we didn't include floating point code in the IR interpreter before is it is harder to make things match up with exactly how things are going to be run if it were JIT'ed into the process. On x86_64 or x64 there are floating point settings that can be changed and affect how operations happen in the current thread. The main example I always think of is how older debuggers would create recursive descent parsers and evaluate floating point operations using native floating point types. I believe that our APFloat classes can do everything correctly, but I would like to see tests that verify that we get the same results as if we were running actual code in the process. For this you can add an extra function to the lldb/test/API/lang/c/fpeval/main.c source like:

  typedef enum FloatOperation { add, subtract, multiply, ... };
  double eval(double a, double b, FloatOperation op) {
    switch (op) {
    case add: return a+b;
    case subtract: return a-b;
    ...
    }
  }



================
Comment at: lldb/test/API/lang/c/fpeval/TestFPEval.py:32
+        self.runCmd("run", RUN_SUCCEEDED)
+        self.expect("expr --allow-jit false  -- a + b", VARIABLES_DISPLAYED_CORRECTLY,
+                    substrs=['double', '44'])
----------------
You might be able to get away with not actually even creating a target or running to main if you define variables in your expression:

```
self.expect('expr --allow-jit false  -- float x=2.2; float y=4.4; x+y', ...
```


================
Comment at: lldb/test/API/lang/c/fpeval/main.c:3-4
+{
+    double a = 42.0;
+    double b = 2.0;
+    return 0; //// Set break point at this line.
----------------
We should be testing "float" and "long double" as well to verify those work.


================
Comment at: lldb/test/API/lang/c/fpeval/main.c:1-10
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+int main (int argc, char const *argv[])
+{
+    double a = 42.0;
----------------
I don't think this file is even needed if you define variables locally in your own expression each time like I mentioned above ("expr float x=2.2; float y=4.4; x+y")


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  https://reviews.llvm.org/D126359/new/

https://reviews.llvm.org/D126359