[clang][DebugInfo] Debug support for private variables inside an OpenMP task construct

[alok]

Summary

Currently variables appearing inside private/firstprivate/lastprivateclause of openmp task construct are not visible inside lldb debugger.
This is because compiler does not generate debug info for it.

Please consider the testcase debug_private.c attached with patch.

   31         priv2 = n + 2;
   32         printf("Task n=%d,priv1=%d,priv2=%d,fpriv=%d\n",n,priv1,priv2,fpriv);
   33
-> 34         res = priv1 + priv2 + fpriv + foo(n - 1);
   35       }
   36   #pragma omp taskwait
   37       return res;
(lldb) p priv1
error: <user expression 0>:1:1: use of undeclared identifier 'priv1'
priv1
^
(lldb) p priv2
error: <user expression 1>:1:1: use of undeclared identifier 'priv2'
priv2
^
(lldb) p fpriv
error: <user expression 2>:1:1: use of undeclared identifier 'fpriv'
fpriv
^

After the current patch, lldb is able to show the variables

(lldb) p priv1
(int) $0 = 10
(lldb) p priv2
(int) $1 = 12
(lldb) p fpriv
(int) $2 = 14

[djtodoro]

Thanks for doing this! Can you please update the summary, since it hard to read with the format like this (at least, just try to reformat the debugger output properly with the Phabricator formatters)?

[alok]

In D114504#3151332, @djtodoro wrote:

Thanks for doing this! Can you please update the summary, since it hard to read with the format like this (at least, just try to reformat the debugger output properly with the Phabricator formatters)?

Sorry for the bad formatting. I have corrected it now.

[djtodoro]

This looks reasonable to me (some nits included).

clang/lib/CodeGen/CGStmtOpenMP.cpp

4513

I think we can get rid of curly brackets.

4515

[alok]

clang/lib/CodeGen/CGStmtOpenMP.cpp

4513

Sure, I am doing it.

4515

Thanks. I am updating it.

[alok]

Re-based and incorporated comments from @djtodoro

[alok]

Thanks @djtodoro . I have incorporated all your comments.

[djtodoro]

LGTM

clang/lib/CodeGen/CGStmtOpenMP.cpp

if (!Data.PrivateVars.empty() || !Data.FirstprivateVars.empty() ||
         Scope.addPrivate(Pair.first, [&CGF, &DRE]() {
           return CGF.EmitLValue(&DRE).getAddress(CGF);
         });
       }
       for (const auto &Pair : PrivatePtrs) {
         Address Replacement(CGF.Builder.CreateLoad(Pair.second),
                             CGF.getContext().getDeclAlign(Pair.first));
         Scope.addPrivate(Pair.first, [Replacement]() { return Replacement; });
+        if (auto *DI = CGF.getDebugInfo())
+          DI->EmitDeclareOfAutoVariable(Pair.first, Pair.second.getPointer(),
+                                        CGF.Builder, /*UsePointerValue*/ true);
       }
       // Adjust mapping for internal locals by mapping actual memory instead of
       // a pointer to this memory.
       for (auto &Pair : UntiedLocalVars) {
         if (isAllocatableDecl(Pair.first)) {
           llvm::Value *Ptr = CGF.Builder.CreateLoad(Pair.second.first);
           Address Replacement(Ptr, CGF.getPointerAlign());
           Pair.second.first = Replacement;

clang/test/OpenMP/debug_private.c

+// This testcase checks emission of debug info for variables inside
+// private/firstprivate/lastprivate.
+
+// REQUIRES: x86_64-linux
+
+// RUN: %clang_cc1 -debug-info-kind=constructor -x c -verify -triple x86_64-pc-linux-gnu -fopenmp -emit-llvm %s -o - | FileCheck %s
+// expected-no-diagnostics
+
+// CHECK: define internal i32 @.omp_task_entry.
+
+// CHECK:  call void @llvm.dbg.declare(metadata i32** %.priv.ptr.addr.i, metadata [[PRIV1:![0-9]+]], metadata !DIExpression(DW_OP_deref))
+// CHECK:  call void @llvm.dbg.declare(metadata i32** %.priv.ptr.addr1.i, metadata [[PRIV2:![0-9]+]], metadata !DIExpression(DW_OP_deref))
+// CHECK:  call void @llvm.dbg.declare(metadata i32** %.firstpriv.ptr.addr.i, metadata [[FPRIV:![0-9]+]], metadata !DIExpression(DW_OP_deref))
+
+// CHECK: [[PRIV1]] = !DILocalVariable(name: "priv1"
+// CHECK: [[PRIV2]] = !DILocalVariable(name: "priv2"
+// CHECK: [[FPRIV]] = !DILocalVariable(name: "fpriv"
+
+extern int printf(const char *, ...);
+
+int foo(int n) {
+  int res, priv1, priv2, fpriv;
+  fpriv = n + 4;
+
+  if (n < 2)
+    return n;
+  else {
+#pragma omp task shared(res) private(priv1, priv2) firstprivate(fpriv)
+    {
+      priv1 = n;
+      priv2 = n + 2;
+      printf("Task n=%d,priv1=%d,priv2=%d,fpriv=%d\n", n, priv1, priv2, fpriv);
+
+      res = priv1 + priv2 + fpriv + foo(n - 1);
+    }
+#pragma omp taskwait
+    return res;
+  }
+}
+
+int main() {
+  int n = 10;
+  printf("foo(%d) = %d\n", n, foo(n));
+  return 0;
+}