[mlir][LLVM] Fix dbg intrinsic import of killed locations

This commit ensures that debug intrinsics of killed variables do not
cause a crash of the importer. Killed locations are usually undef
constants, but in infrequent cases can also be metadata nodes, which
caused problems.

Reviewed By: zero9178

Differential Revision: https://reviews.llvm.org/D157724

Author: Dinistro

mlir/lib/Target/LLVMIR/ModuleImport.cpp

@@ -1750,6 +1750,18 @@ LogicalResult ModuleImport::processFunction(llvm::Function *func) {
   return success();
 }
 
+/// Checks if `dbgIntr` is a kill location that holds metadata instead of an SSA
+/// value.
+static bool isMetadataKillLocation(llvm::DbgVariableIntrinsic *dbgIntr) {
+  if (!dbgIntr->isKillLocation())
+    return false;
+  llvm::Value *value = dbgIntr->getArgOperand(0);
+  auto *nodeAsVal = dyn_cast<llvm::MetadataAsValue>(value);
+  if (!nodeAsVal)
+    return false;
+  return !isa<llvm::ValueAsMetadata>(nodeAsVal->getMetadata());
+}
+
 LogicalResult
 ModuleImport::processDebugIntrinsic(llvm::DbgVariableIntrinsic *dbgIntr,
                                     DominanceInfo &domInfo) {
@@ -1763,9 +1775,15 @@ ModuleImport::processDebugIntrinsic(llvm::DbgVariableIntrinsic *dbgIntr,
   // TODO: Support debug intrinsics that evaluate a debug expression.
   if (dbgIntr->hasArgList() || dbgIntr->getExpression()->getNumElements() != 0)
     return emitUnsupportedWarning();
+  // Kill locations can have metadata nodes as location operand. This
+  // cannot be converted to poison as the type cannot be reconstructed.
+  // TODO: find a way to support this case.
+  if (isMetadataKillLocation(dbgIntr))
+    return emitUnsupportedWarning();
   FailureOr<Value> argOperand = convertMetadataValue(dbgIntr->getArgOperand(0));
   if (failed(argOperand))
-    return failure();
+    return emitError(loc) << "failed to convert a debug intrinsic operand: "
+                          << diag(*dbgIntr);
 
   // Ensure that the debug instrinsic is inserted right after its operand is
   // defined. Otherwise, the operand might not necessarily dominate the

mlir/test/Target/LLVMIR/Import/import-failure.ll

@@ -65,9 +65,12 @@ declare void @llvm.dbg.value(metadata, metadata, metadata)
 ; CHECK-SAME: warning: dropped intrinsic: call void @llvm.dbg.value(metadata i64 %arg1, metadata !3, metadata !DIExpression(DW_OP_plus_uconst, 42, DW_OP_stack_value)), !dbg !5
 ; CHECK:      import-failure.ll
 ; CHECK-SAME: warning: dropped intrinsic: call void @llvm.dbg.value(metadata !DIArgList(i64 %arg1, i64 undef), metadata !3, metadata !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_constu, 1, DW_OP_mul, DW_OP_plus, DW_OP_stack_value)), !dbg !5
+; CHECK:      import-failure.ll
+; CHECK-SAME: warning: dropped intrinsic: call void @llvm.dbg.value(metadata !6, metadata !3, metadata !DIExpression()), !dbg !5
 define void @dropped_instruction(i64 %arg1) {
   call void @llvm.dbg.value(metadata i64 %arg1, metadata !3, metadata !DIExpression(DW_OP_plus_uconst, 42, DW_OP_stack_value)), !dbg !5
   call void @llvm.dbg.value(metadata !DIArgList(i64 %arg1, i64 undef), metadata !3, metadata !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_constu, 1, DW_OP_mul, DW_OP_plus, DW_OP_stack_value)), !dbg !5
+  call void @llvm.dbg.value(metadata !6, metadata !3, metadata !DIExpression()), !dbg !5
   ret void
 }
 
@@ -79,6 +82,7 @@ define void @dropped_instruction(i64 %arg1) {
 !3 = !DILocalVariable(scope: !4, name: "arg1", file: !2, line: 1, arg: 1, align: 64);
 !4 = distinct !DISubprogram(name: "intrinsic", scope: !2, file: !2, spFlags: DISPFlagDefinition, unit: !1)
 !5 = !DILocation(line: 1, column: 2, scope: !4)
+!6 = !{}
 
 ; // -----