[llvm] [ADT] Don't use getEmptyKey() when hashing std::optional (PR #202002)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-adt

Author: Fangrui Song (MaskRay)

<details>
<summary>Changes</summary>

DenseMapInfo<std::optional<T>>::getHashValue() calls T's getEmptyKey()
for the nullopt case. This blocks removing the now-unused getEmptyKey()
from DenseMapInfo specializations: a leaf type that drops getEmptyKey()
fails to compile wherever std::optional<T> is used as a DenseMap key
(e.g. DenseMapInfo<mlir::spirv::StorageClass>).

Compute the hash directly instead. Prerequisite for the getEmptyKey()
removal series; #<!-- -->201281 made getEmptyKey() unused by DenseMap.


---
Full diff: https://github.com/llvm/llvm-project/pull/202002.diff


1 Files Affected:

- (modified) llvm/include/llvm/ADT/DenseMapInfo.h (+3-3) 


``````````diff
diff --git a/llvm/include/llvm/ADT/DenseMapInfo.h b/llvm/include/llvm/ADT/DenseMapInfo.h
index e8e21e4a15e66..f5c60a70ea805 100644
--- a/llvm/include/llvm/ADT/DenseMapInfo.h
+++ b/llvm/include/llvm/ADT/DenseMapInfo.h
@@ -214,9 +214,9 @@ template <typename T> struct DenseMapInfo<std::optional<T>> {
   static constexpr Optional getEmptyKey() { return {Info::getEmptyKey()}; }
 
   static unsigned getHashValue(const Optional &OptionalVal) {
-    return detail::combineHashValue(
-        OptionalVal.has_value(),
-        Info::getHashValue(OptionalVal.value_or(Info::getEmptyKey())));
+    if (OptionalVal)
+      return detail::combineHashValue(1, Info::getHashValue(*OptionalVal));
+    return detail::combineHashValue(0, 0);
   }
 
   static bool isEqual(const Optional &LHS, const Optional &RHS) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/202002