[MLIR][LLVM] CallSiteLoc without caller scope not translatable (#90759)

If a CallSiteLoc's caller cannot be translated (returns null), we cannot
simply return the translation of the callee location. This is because
the resulting DILocation will not have any InlinedAt field for the
function it is in, and will fail the LLVM IR verifier.

Author: zyx-billy

mlir/lib/Target/LLVMIR/DebugTranslation.cpp

@@ -406,6 +406,10 @@ llvm::DILocation *DebugTranslation::translateLoc(Location loc,
   if (auto callLoc = dyn_cast<CallSiteLoc>(loc)) {
     // For callsites, the caller is fed as the inlinedAt for the callee.
     auto *callerLoc = translateLoc(callLoc.getCaller(), scope, inlinedAt);
+    // If the caller scope does not exist, the callsite cannot be represented
+    // in LLVM (the callee scope may not match the function it is in).
+    if (!callerLoc)
+      return nullptr;
     llvmLoc = translateLoc(callLoc.getCallee(), nullptr, callerLoc);
     // Fallback: Ignore callee if it has no debug scope.
     if (!llvmLoc)

mlir/test/Target/LLVMIR/llvmir-debug.mlir

@@ -108,12 +108,15 @@ llvm.func @func_with_debug(%arg: i64) {
   // CHECK: call void @func_no_debug(), !dbg ![[NAMED_LOC:[0-9]+]]
   llvm.call @func_no_debug() : () -> () loc("named"("foo.mlir":10:10))
 
-  // CHECK: call void @func_no_debug(), !dbg ![[CALLSITE_LOC:[0-9]+]]
+  // CHECK: call void @func_no_debug(), !dbg ![[MY_SOURCE_LOC:[0-9]+]]
   llvm.call @func_no_debug() : () -> () loc(callsite("nodebug.cc":3:4 at "mysource.cc":5:6))
 
-  // CHECK: call void @func_no_debug(), !dbg ![[CALLSITE_LOC:[0-9]+]]
+  // CHECK: call void @func_no_debug(), !dbg ![[MY_SOURCE_LOC]]
   llvm.call @func_no_debug() : () -> () loc(callsite("nodebug.cc":3:4 at fused<#sp0>["mysource.cc":5:6]))
 
+  // CHECK: call void @func_no_debug(), !dbg ![[MY_SOURCE_LOC]]
+  llvm.call @func_no_debug() : () -> () loc(callsite(callsite(fused<#callee>["nodebug.cc":3:4] at "foo.mlir":2:4) at fused<#sp0>["mysource.cc":5:6]))
+
   // CHECK: call void @func_no_debug(), !dbg ![[FUSED_LOC:[0-9]+]]
   llvm.call @func_no_debug() : () -> () loc(fused[callsite(fused<#callee>["mysource.cc":5:6] at "mysource.cc":1:1), "mysource.cc":1:1])
 
@@ -153,7 +156,7 @@ llvm.func @empty_types() {
 // CHECK: ![[BLOCK_LOC]] = distinct !DILexicalBlock(scope: ![[FUNC_LOC]])
 // CHECK: ![[NO_NAME_VAR]] = !DILocalVariable(scope: ![[BLOCK_LOC]])
 
-// CHECK-DAG: ![[CALLSITE_LOC]] = !DILocation(line: 5, column: 6,
+// CHECK-DAG: ![[MY_SOURCE_LOC]] = !DILocation(line: 5, column: 6
 // CHECK-DAG: ![[FILE_LOC]] = !DILocation(line: 1, column: 2,
 // CHECK-DAG: ![[NAMED_LOC]] = !DILocation(line: 10, column: 10
 // CHECK-DAG: ![[FUSED_LOC]] = !DILocation(line: 1, column: 1