[lldb] [llvm] [DebugInfo][LLDB] Fix generic DW_OP_const handling (PR #204353)

[Bevin Hansson via llvm-commits]

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@@ -3251,10 +3252,39 @@ void DwarfDebug::emitDebugLocValue(const AsmPrinter &AP, const DIBasicType *BT,
                             &AP](const DbgValueLocEntry &Entry,
                                  DIExpressionCursor &Cursor) -> bool {
     if (Entry.isInt()) {
-      if (BT && (BT->getEncoding() == dwarf::DW_ATE_boolean))
+      if (BT && (BT->getEncoding() == dwarf::DW_ATE_boolean)) {
         DwarfExpr.addBooleanConstant(Entry.getInt());
-      else if (BT && (BT->getEncoding() == dwarf::DW_ATE_signed ||
-                      BT->getEncoding() == dwarf::DW_ATE_signed_char))
+        return true;
+      }
+
+      bool IsSigned = BT && (BT->getEncoding() == dwarf::DW_ATE_signed ||
+                             BT->getEncoding() == dwarf::DW_ATE_signed_char);
+      if (BT && AP.getDwarfVersion() >= 4 &&
+          !AP.getDwarfDebug()->tuneForSCE() && !Cursor) {
+        // DW_OP_const* pushes a generic, address-sized value. For a wider
+        // source integer value that cannot fit in the generic type, use
+        // DW_OP_implicit_value to preserve the source bytes instead. Keep this
+        // limited to complete constant values: SCE tuning already avoids
+        // DW_OP_implicit_value for compatibility, and expressions with
+        // remaining operations may need a scalar stack value rather than an
+        // implicit value block.
+        unsigned GenericBitSize = AP.MAI.getCodePointerSize() * 8;
+        uint64_t TypeBitSize = BT->getSizeInBits();
+        bool IsByteSized = TypeBitSize % 8 == 0;
+        bool IsOutOfRange =
+            IsSigned ? !isIntN(GenericBitSize, Entry.getInt())
+                     : !isUIntN(GenericBitSize,
+                                static_cast<uint64_t>(Entry.getInt()));
+        if (TypeBitSize > GenericBitSize && IsByteSized && IsOutOfRange) {
+          DwarfExpr.addImplicitValue(
+              APInt(static_cast<unsigned>(TypeBitSize),
+                    static_cast<uint64_t>(Entry.getInt()), IsSigned),
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bevin-hansson wrote:

We're seeing assertion failures on this downstream. If `64 > TypeBitSize > GenericBitSize` and `Entry.getInt()` has bits outside of `TypeBitSize`, APInt triggers an assertion as `ImplicitTrunc` is false by default.

https://github.com/llvm/llvm-project/pull/204353