[flang] Check for BIND(C) name conflicts with alternate entries

[eugeneepshteyn]

Added IsAlternateEntry() and modified IsExternalProcedureDefinition() to also check for alternate entries.

(IsExternalProcedureDefinition() is called from CheckHelper::CheckGlobalName(), which checks for duplicate global symbols.)

Fixes #62778

[klausler]

It would be more clear to implement these in the opposite way, I think.

[eugeneepshteyn]

You mean have IsAlternateEntry(&symbol) be primary and IsAlternateEntry(*symbol) call it? I started it that way, but because GetMainEntry() returns a pointer, it looked somewhat less clean.

[klausler]

If you only have one call site, then you don't need both APIs (yet).

I have been slowing converting tools like this -- ones with reasonable results for absent (null) pointer arguments -- into pointer-only forms, as I run across hem.

[eugeneepshteyn]

Ok, I only left IsAlternateEntry() that accepts the pointer, because it still looks cleaner to me.

[llvmbot]

@llvm/pr-subscribers-flang-semantics

Author: Eugene Epshteyn (eugeneepshteyn)

Changes

Added IsAlternateEntry() and modified IsExternalProcedureDefinition() to also check for alternate entries.

(IsExternalProcedureDefinition() is called from CheckHelper::CheckGlobalName(), which checks for duplicate global symbols.)

Fixes #62778

---

Full diff: https://github.com/llvm/llvm-project/pull/156563.diff

3 Files Affected:

• (modified) flang/include/flang/Evaluate/tools.h (+6)
• (modified) flang/lib/Semantics/check-declarations.cpp (+1-1)
• (modified) flang/test/Semantics/bind-c01.f90 (+8)

diff --git a/flang/include/flang/Evaluate/tools.h b/flang/include/flang/Evaluate/tools.h
index 225e1a77f041b..5f2f199e778c7 100644
--- a/flang/include/flang/Evaluate/tools.h
+++ b/flang/include/flang/Evaluate/tools.h
@@ -1531,6 +1531,12 @@ class Scope;
 // point to its subprogram.
 const Symbol *GetMainEntry(const Symbol *);
 
+inline bool IsAlternateEntry(const Symbol *symbol) {
+  // If symbol is not alternate entry symbol, GetMainEntry() returns the same
+  // symbol.
+  return symbol && GetMainEntry(symbol) != symbol;
+}
+
 // These functions are used in Evaluate so they are defined here rather than in
 // Semantics to avoid a link-time dependency on Semantics.
 // All of these apply GetUltimate() or ResolveAssociations() to their arguments.
diff --git a/flang/lib/Semantics/check-declarations.cpp b/flang/lib/Semantics/check-declarations.cpp
index b9f5737468ff8..84edcebc64973 100644
--- a/flang/lib/Semantics/check-declarations.cpp
+++ b/flang/lib/Semantics/check-declarations.cpp
@@ -2950,7 +2950,7 @@ static bool IsSubprogramDefinition(const Symbol &symbol) {
 
 static bool IsExternalProcedureDefinition(const Symbol &symbol) {
   return IsBlockData(symbol) ||
-      (IsSubprogramDefinition(symbol) &&
+      ((IsSubprogramDefinition(symbol) || IsAlternateEntry(&symbol)) &&
           (IsExternal(symbol) || symbol.GetBindName()));
 }
 
diff --git a/flang/test/Semantics/bind-c01.f90 b/flang/test/Semantics/bind-c01.f90
index f0546b3eb068c..79d53677abc9d 100644
--- a/flang/test/Semantics/bind-c01.f90
+++ b/flang/test/Semantics/bind-c01.f90
@@ -29,3 +29,11 @@ subroutine foo() bind(c, name="x6")
 end subroutine
 subroutine foo() bind(c, name="x7")
 end subroutine
+
+subroutine entries()
+
+entry e1() bind(C, name="e")
+
+!ERROR: Two entities have the same global name 'e'
+entry e2() bind(C, name="e")
+end subroutine