[llvm] [BOLT] Add heuristics to determine constant island's alignment (PR #159486)

[Maksim Panchenko via llvm-commits]

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@@ -284,6 +284,33 @@ BinaryFunction::getBasicBlockContainingOffset(uint64_t Offset) {
   return (Offset < BB->getOffset() + BB->getOriginalSize()) ? BB : nullptr;
 }
 
+uint16_t BinaryFunction::getConstantIslandAlignment() const {
+  if (Islands == nullptr)
+    return 1;
+
+  // For constant island inside a function, the default 8-byte alignment is
+  // probably good enough.
+  const uint16_t DefaultAlignment = sizeof(uint64_t);
+  if (!isDataObject())
+    return DefaultAlignment;
+
+  // If the constant island itself is a binary function, get its alignment
+  // based on its size, original address, and its owning section's alignment.
+  uint64_t MaxAlignment =
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maksfb wrote:

nit: constify variables that don't change.

https://github.com/llvm/llvm-project/pull/159486