[llvm] [RemoveDIs] Read/write DbgRecords directly from/to bitcode (PR #83251)

[Orlando Cazalet-Hyams via llvm-commits]

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@@ -3491,25 +3495,93 @@ void ModuleBitcodeWriter::writeFunction(
       NeedsMetadataAttachment |= I.hasMetadataOtherThanDebugLoc();
 
       // If the instruction has a debug location, emit it.
-      DILocation *DL = I.getDebugLoc();
-      if (!DL)
-        continue;
-
-      if (DL == LastDL) {
-        // Just repeat the same debug loc as last time.
-        Stream.EmitRecord(bitc::FUNC_CODE_DEBUG_LOC_AGAIN, Vals);
-        continue;
+      if (DILocation *DL = I.getDebugLoc()) {
+        if (DL == LastDL) {
+          // Just repeat the same debug loc as last time.
+          Stream.EmitRecord(bitc::FUNC_CODE_DEBUG_LOC_AGAIN, Vals);
+        } else {
+          Vals.push_back(DL->getLine());
+          Vals.push_back(DL->getColumn());
+          Vals.push_back(VE.getMetadataOrNullID(DL->getScope()));
+          Vals.push_back(VE.getMetadataOrNullID(DL->getInlinedAt()));
+          Vals.push_back(DL->isImplicitCode());
+          Stream.EmitRecord(bitc::FUNC_CODE_DEBUG_LOC, Vals);
+          Vals.clear();
+          LastDL = DL;
+        }
       }
 
-      Vals.push_back(DL->getLine());
-      Vals.push_back(DL->getColumn());
-      Vals.push_back(VE.getMetadataOrNullID(DL->getScope()));
-      Vals.push_back(VE.getMetadataOrNullID(DL->getInlinedAt()));
-      Vals.push_back(DL->isImplicitCode());
-      Stream.EmitRecord(bitc::FUNC_CODE_DEBUG_LOC, Vals);
-      Vals.clear();
-
-      LastDL = DL;
+      // If the instruction has DPValues attached to it, emit them. Note that
+      // they come after the instruction so that it's easy to attach them again
+      // when reading the bitcode, even though conceptually the debug locations
+      // start "before" the instruction.
+      if (I.hasDbgValues() && WriteNewDbgInfoFormatToBitcode) {
+        /// Try to push the value only (unwrapped), otherwise push the
+        /// metadata wrapped value. Returns true if the value was pushed
+        /// without the ValueAsMetadata wrapper.
+        auto PushValueOrMetadata = [&Vals, InstID, this](Metadata *RawLocation) {
+          assert(RawLocation && "RawLocation unexpectedly null in DPValue");
+          if (ValueAsMetadata *VAM = dyn_cast<ValueAsMetadata>(RawLocation)) {
+            SmallVector<unsigned, 2> ValAndType;
+            // If the value is a fwd-ref the type is also pushed. We don't
+            // want the type, so fwd-refs are kept wrapped (pushValueAndType
+            // returns false if the value is pushed without type).
+            if (!pushValueAndType(VAM->getValue(), InstID, ValAndType)) {
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OCHyams wrote:

Yeah that's right. It saves us needing to encode the fwd-ref type, which would result in an extra field in the abbrev that is nonzero for < 1% of records.

https://github.com/llvm/llvm-project/pull/83251