[mlir][llvm] Use before def debug intrinsic import

[Dinistro]

Summary

This commit adds special handling for the debug intrinsic value
handling. LLVM allows to relax the def before use property for debug
intrinsics, so this property cannot be assumed for metadata values.

[Dinistro]

rebased

[gysit]

LGTM

mlir/include/mlir/Dialect/LLVMIR/LLVMIntrinsicOps.td

let mlirBuilder = [{
     auto *dbgIntr = cast<llvm::DbgVariableIntrinsic>(inst);
     if (dbgIntr->hasArgList() || dbgIntr->getExpression()->getNumElements() != 0)
       return success();
     // Convert the value/address operand late since it cannot be a debug
     // metadata argument list at this stage. Generating the conversion using an
     // argument variable would not work here, since the builder variables are
     // converted before entering the builder, which would result in an error
     // when attempting to convert an argument list.
-    FailureOr<Value> argOperand = moduleImport.convertValue(llvmOperands[0]);
+
+    FailureOr<Value> argOperand = moduleImport.convertMetadataValue(llvmOperands[0]);
+    // Drop the intrinsic when its operand could not be converted. This can
+    // happen for use before definition cases that are allowed for debug
+    // intrinsics.
     if (failed(argOperand))
-      return failure();
+      return success();
     $_op = $_builder.create<$_qualCppClassName>($_location,
         *argOperand, $_var_attr($varInfo));
   }];
   let assemblyFormat = [{
     qualified($varInfo) `=` $}] # argName #
       [{ `:` qualified(type($}] # argName # [{)) attr-dict
   }];
 }

mlir/include/mlir/Target/LLVMIR/ModuleImport.h

Block *lookupBlock(llvm::BasicBlock *block) const {
     return blockMapping.lookup(block);
   }
 
   /// Converts an LLVM value to an MLIR value, or returns failure if the
   /// conversion fails. Uses the `convertConstant` method to translate constant
   /// LLVM values.
   FailureOr<Value> convertValue(llvm::Value *value);
 
+  /// Converts an LLVM metadata value to an MLIR value, or returns failure if
+  /// the conversion fails. Uses the `convertConstant` method to translate
+  /// constant LLVM values.
+  FailureOr<Value> convertMetadataValue(llvm::Value *value);
+
   /// Converts a range of LLVM values to a range of MLIR values using the
   /// `convertValue` method, or returns failure if the conversion fails.
   FailureOr<SmallVector<Value>> convertValues(ArrayRef<llvm::Value *> values);
 
   /// Converts `value` to an integer attribute. Asserts if the matching fails.
   IntegerAttr matchIntegerAttr(llvm::Value *value);
 
   /// Converts `value` to a local variable attribute. Asserts if the matching

mlir/lib/Target/LLVMIR/ModuleImport.cpp

FailureOr<Value> ModuleImport::convertConstantExpr(llvm::Constant *constant) {
 
   // Update the constant insertion point and return the converted constant.
   Value result = lookupValue(constant);
   constantInsertionOp = result.getDefiningOp();
   return result;
 }
 
 FailureOr<Value> ModuleImport::convertValue(llvm::Value *value) {
-  // A value may be wrapped as metadata, for example, when passed to a debug
-  // intrinsic. Unwrap these values before the conversion.
-  if (auto *nodeAsVal = dyn_cast<llvm::MetadataAsValue>(value))
-    if (auto *node = dyn_cast<llvm::ValueAsMetadata>(nodeAsVal->getMetadata()))
-      value = node->getValue();
+  assert(!isa<llvm::MetadataAsValue>(value) &&
+         "expected value to not be metadata");
 
   // Return the mapped value if it has been converted before.
   if (valueMapping.count(value))
     return lookupValue(value);
 
   // Convert constants such as immediate values that have no mapping yet.
   if (auto *constant = dyn_cast<llvm::Constant>(value))
     return convertConstantExpr(constant);
 
   Location loc = mlirModule.getLoc();
   if (auto *inst = dyn_cast<llvm::Instruction>(value))
     loc = translateLoc(inst->getDebugLoc());
   return emitError(loc) << "unhandled value: " << diag(*value);
 }
 
+FailureOr<Value> ModuleImport::convertMetadataValue(llvm::Value *value) {
+  // A value may be wrapped as metadata, for example, when passed to a debug
+  // intrinsic. Unwrap these values before the conversion.
+  auto *nodeAsVal = dyn_cast<llvm::MetadataAsValue>(value);
+  if (!nodeAsVal)
+    return failure();
+  auto *node = dyn_cast<llvm::ValueAsMetadata>(nodeAsVal->getMetadata());
+  if (!node)
+    return failure();
+  value = node->getValue();
+
+  // Return the mapped value if it has been converted before.
+  if (valueMapping.count(value))
+    return lookupValue(value);
+
+  // Convert constants such as immediate values that have no mapping yet.
+  if (auto *constant = dyn_cast<llvm::Constant>(value))
+    return convertConstantExpr(constant);
+  return failure();
+}
+
 FailureOr<SmallVector<Value>>
 ModuleImport::convertValues(ArrayRef<llvm::Value *> values) {
   SmallVector<Value> remapped;
   remapped.reserve(values.size());
   for (llvm::Value *value : values) {
     FailureOr<Value> converted = convertValue(value);
     if (failed(converted))
       return failure();

mlir/test/Target/LLVMIR/Import/debug-info.ll

 !llvm.dbg.cu = !{!1}
 !llvm.module.flags = !{!0}
 !0 = !{i32 2, !"Debug Info Version", i32 3}
 !1 = distinct !DICompileUnit(language: DW_LANG_C, file: !2)
 !2 = !DIFile(filename: "debug-info.ll", directory: "/")
 !3 = !DISubprogram(name: "variadic_func", scope: !2, file: !2, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, type: !4)
 !4 = !DISubroutineType(types: !5)
 !5 = !{null, null}
+
+; // -----
+
+define void @dbg_use_before_def(ptr %arg) {
+  call void @llvm.dbg.value(metadata ptr %dbg_arg, metadata !7, metadata !DIExpression()), !dbg !9
+  %dbg_arg = getelementptr double, ptr %arg, i64 16
+  ret void
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!1}
+!llvm.module.flags = !{!0}
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = distinct !DICompileUnit(language: DW_LANG_C, file: !2)
+!2 = !DIFile(filename: "debug-info.ll", directory: "/")
+!3 = !DICompositeType(tag: DW_TAG_class_type, name: "class_field", file: !2, line: 42, flags: DIFlagTypePassByReference | DIFlagNonTrivial, elements: !4)
+!4 = !{!6}
+!5 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !3, flags: DIFlagArtificial | DIFlagObjectPointer)
+!6 = !DIDerivedType(tag: DW_TAG_member, name: "call_field", file: !2, baseType: !5)
+!7 = !DILocalVariable(scope: !8, name: "var", file: !2, type: !5);
+!8 = distinct !DISubprogram(name: "dbg_use_before_def", scope: !2, file: !2, spFlags: DISPFlagDefinition, unit: !1)
+!9 = !DILocation(line: 1, column: 2, scope: !8)