[llvm] [DebugInfo] Use DW_OP_deref_size for DW_OP_LLVM_extract_bits (PR #97609)

[Stephen Tozer via llvm-commits]

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@@ -552,9 +552,13 @@ bool DwarfExpression::addExpression(
       unsigned SizeInBits = Op->getArg(1);
       unsigned BitOffset = Op->getArg(0);
 
-      // If we have a memory location then dereference to get the value
-      if (isMemoryLocation())
-        emitOp(dwarf::DW_OP_deref);
+      // If we have a memory location then dereference to get the value, though
+      // we have to make sure we don't dereference any bytes past the end of the
+      // object.
+      if (isMemoryLocation()) {
+        emitOp(dwarf::DW_OP_deref_size);
+        emitUnsigned(alignTo(BitOffset + SizeInBits, 8) / 8);
+      }
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SLTozer wrote:

I think ideally we'd only use `DW_OP_deref_size` if `DW_OP_deref` will actually dereference too many bytes, but that's a minor point.

https://github.com/llvm/llvm-project/pull/97609