[Mlir-commits] [mlir] [MLIR][LLVM] CallSiteLoc without caller scope not translatable (PR #90759)

[Billy Zhu]

https://github.com/zyx-billy created https://github.com/llvm/llvm-project/pull/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.

---

Example:

This situation occurs when we have a nested callsite loc, where the middle function in the stack does not have a debug scope
```
func A {
  foo loc(fused<#A>["a":1:1])
}
func B {
  call @A loc("b":1:1)
}
func C {
  call @B loc(fused<#C>["c":1:1])
}
```
When A is inlined into B, and B is inlined into C, we get
```
func C {
  foo loc(callsite(
            callsite(fused<#A>["a":1:1] at loc("b":1:1))
           at
            fused<#C>["c":1:1]))
}
```
We do not want to translate this into just a `!DILocation(line: 1, column: 1, scope: !A)`, as that would not be legal in func C, so this is not something we can represent in LLVM IR.

>From 349d34f4967be3ba8f1015d90900f09ff51cb582 Mon Sep 17 00:00:00 2001
From: Billy Zhu <billyzhu at modular.com>
Date: Wed, 1 May 2024 10:44:49 -0700
Subject: [PATCH] no translation for callsite without caller

---
 mlir/lib/Target/LLVMIR/DebugTranslation.cpp | 4 ++++
 mlir/test/Target/LLVMIR/llvmir-debug.mlir   | 9 ++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/mlir/lib/Target/LLVMIR/DebugTranslation.cpp b/mlir/lib/Target/LLVMIR/DebugTranslation.cpp
index 2de5e372d88c0e..f02939abc5fe18 100644
--- a/mlir/lib/Target/LLVMIR/DebugTranslation.cpp
+++ b/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)
diff --git a/mlir/test/Target/LLVMIR/llvmir-debug.mlir b/mlir/test/Target/LLVMIR/llvmir-debug.mlir
index 8ab1a1b290dad3..e8a3d65209afde 100644
--- a/mlir/test/Target/LLVMIR/llvmir-debug.mlir
+++ b/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