[llvm] Update the EBO static_assert to dheck against APFloat::Storage instead of IEEEFloat. (PR #112589)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-support

Author: Daniel Chen (DanielCChen)

<details>
<summary>Changes</summary>

The addition of the the following code in commit https://github.com/llvm/llvm-project/commit/6004f5550c8032f4c632cdbf5dbc0894bb33e51f#diff-3ec11da67f69353fd755e59cc71f551b5e93773fd4e6f6327c7f1c7074a82709R1474

```
static_assert(sizeof(APFloat) == sizeof(detail::IEEEFloat),
              "Empty base class optimization is not performed.");
 ```
              
broke our downstream code as not all the members of APFloat is IEEE.

This PR supersedes PR #<!-- -->111780. 

We made some changed to our downstream code to accommodate the upstream change. 
This PR is to modify the EBO static_assert to check against the `sizeof(APFloat::Storage)` instead of `sizeof(detail::IEEEFloat)`, which seems satisfy both upstream and downstream code.  
We also moved the assert to `APFloat.cpp` from the header file as per discussion in PR #<!-- -->111780 

@<!-- -->Ariel-Burton

---
Full diff: https://github.com/llvm/llvm-project/pull/112589.diff


2 Files Affected:

- (modified) llvm/include/llvm/ADT/APFloat.h (+1-3) 
- (modified) llvm/lib/Support/APFloat.cpp (+5) 


``````````diff
diff --git a/llvm/include/llvm/ADT/APFloat.h b/llvm/include/llvm/ADT/APFloat.h
index 97547fb577e0ec..85e17efd1fba8e 100644
--- a/llvm/include/llvm/ADT/APFloat.h
+++ b/llvm/include/llvm/ADT/APFloat.h
@@ -1474,11 +1474,9 @@ class APFloat : public APFloatBase {
   friend APFloat frexp(const APFloat &X, int &Exp, roundingMode RM);
   friend IEEEFloat;
   friend DoubleAPFloat;
+  friend class APFloatEBOChecker;
 };
 
-static_assert(sizeof(APFloat) == sizeof(detail::IEEEFloat),
-              "Empty base class optimization is not performed.");
-
 /// See friend declarations above.
 ///
 /// These additional declarations are required in order to compile LLVM with IBM
diff --git a/llvm/lib/Support/APFloat.cpp b/llvm/lib/Support/APFloat.cpp
index a33b6c4a6ddc63..f48c82b6afdd89 100644
--- a/llvm/lib/Support/APFloat.cpp
+++ b/llvm/lib/Support/APFloat.cpp
@@ -99,6 +99,11 @@ enum class fltNanEncoding {
   NegativeZero,
 };
 
+class APFloatEBOChecker {
+  static_assert(sizeof(APFloat) == sizeof(APFloat::U),
+                "Empty base class optimization is not performed.");
+};
+
 /* Represents floating point arithmetic semantics.  */
 struct fltSemantics {
   /* The largest E such that 2^E is representable; this matches the

``````````

</details>


https://github.com/llvm/llvm-project/pull/112589