[llvm] [mlir] [DebugInfo] Add symbolic branches to DIExpression (PR #210850)

[Aman LaChapelle via llvm-commits]

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@@ -69,11 +90,36 @@ void DIEDwarfExpression::enableTemporaryBuffer() {
 void DIEDwarfExpression::disableTemporaryBuffer() { IsBuffering = false; }
 
 unsigned DIEDwarfExpression::getTemporaryBufferSize() {
-  return TmpDIE.computeSize(AP.getDwarfFormParams());
+  unsigned Size = 0;
+  for (const DIEValue &V : TmpDIE.values())
+    Size += V.sizeOf(AP.getDwarfFormParams());
+  return Size;
 }
 
 void DIEDwarfExpression::commitTemporaryBuffer() { OutDIE.takeValues(TmpDIE); }
 
+void DIEDwarfExpression::replaceTemporaryBufferData(unsigned Offset,
+                                                    uint64_t Value,
+                                                    unsigned Size) {
+  dwarf::Form Form = getDataForm(Size);
+  // Keep the form so replacing the value doesn't move later labels.
+  unsigned CurrentOffset = 0;
+  for (DIEValue &V : TmpDIE.values()) {
+    unsigned ValueSize = V.sizeOf(AP.getDwarfFormParams());
+    if (Offset < CurrentOffset + ValueSize) {
+      assert(Offset == CurrentOffset && ValueSize == Size &&
+             V.getType() == DIEValue::isInteger && V.getForm() == Form &&
+             V.getDIEInteger().getValue() == 0 &&
+             "symbolic branch fixup does not match its placeholder");
+      V = DIEValue(V.getAttribute(), V.getForm(),
+                   DIEInteger(getDataValue(Value, Size)));
+      return;
+    }
+    CurrentOffset += ValueSize;
+  }
+  llvm_unreachable("invalid temporary DIE offset");
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bzcheeseman wrote:

This control flow feels off - what is the expected behavior if one of the TmpDIE values  hits the `if (Offset < CurrentOffset + ValueSize)` branch before you've resolved all the fixups? Or alternatively, what if TmpDIE has entries that don't require fixups?

https://github.com/llvm/llvm-project/pull/210850