Use primary template parameter names for variable template debug info

Summary:
Fixes PR41677

Consider:
  template <typename LHS, typename RHS> constexpr bool is_same_v = false;
  template <typename T> constexpr bool is_same_v<T, T> = true;
  template constexpr bool is_same_v<int, int>;

Before this change, when emitting debug info for the
`is_same_v<int, int>` global variable, clang would crash because it
would try to use the template parameter list from the partial
specialization to give parameter names to template arguments. This
doesn't work in general, since a partial specialization can have fewer
arguments than the primary template. Therefore, always use the primary
template. Hypothetically we could try to use the parameter names from
the partial specialization when possible, but it's not clear this really
helps debugging in practice.

Reviewers: JDevlieghere, aprantl, ormris, dblaikie

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D61408

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@359809 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 32 insertions, 23 deletions

diff --git a/lib/CodeGen/CGDebugInfo.cpp b/lib/CodeGen/CGDebugInfo.cpp
index 80d3484623..3656602c3d 100644
--- a/lib/CodeGen/CGDebugInfo.cpp
+++ b/lib/CodeGen/CGDebugInfo.cpp
@@ -1827,32 +1827,24 @@ CGDebugInfo::CollectFunctionTemplateParams(const FunctionDecl *FD,
 }
 
 llvm::DINodeArray CGDebugInfo::CollectVarTemplateParams(const VarDecl *VL,
-    llvm::DIFile *Unit) {
-  if (auto *TS = dyn_cast<VarTemplateSpecializationDecl>(VL)) {
-    auto T = TS->getSpecializedTemplateOrPartial();
-    auto TA = TS->getTemplateArgs().asArray();
-    // Collect parameters for a partial specialization
-    if (T.is<VarTemplatePartialSpecializationDecl *>()) {
-      const TemplateParameterList *TList =
-        T.get<VarTemplatePartialSpecializationDecl *>()
-        ->getTemplateParameters();
-      return CollectTemplateParams(TList, TA, Unit);
-    }
-
-    // Collect parameters for an explicit specialization
-    if (T.is<VarTemplateDecl *>()) {
-      const TemplateParameterList *TList = T.get<VarTemplateDecl *>()
-        ->getTemplateParameters();
-      return CollectTemplateParams(TList, TA, Unit);
-    }
-  }
-  return llvm::DINodeArray();
+                                                        llvm::DIFile *Unit) {
+  // Always get the full list of parameters, not just the ones from the
+  // specialization. A partial specialization may have fewer parameters than
+  // there are arguments.
+  auto *TS = dyn_cast<VarTemplateSpecializationDecl>(VL);
+  if (!TS)
+    return llvm::DINodeArray();
+  VarTemplateDecl *T = TS->getSpecializedTemplate();
+  const TemplateParameterList *TList = T->getTemplateParameters();
+  auto TA = TS->getTemplateArgs().asArray();
+  return CollectTemplateParams(TList, TA, Unit);
 }
 
 llvm::DINodeArray CGDebugInfo::CollectCXXTemplateParams(
     const ClassTemplateSpecializationDecl *TSpecial, llvm::DIFile *Unit) {
-  // Always get the full list of parameters, not just the ones from
-  // the specialization.
+  // Always get the full list of parameters, not just the ones from the
+  // specialization. A partial specialization may have fewer parameters than
+  // there are arguments.
   TemplateParameterList *TPList =
       TSpecial->getSpecializedTemplate()->getTemplateParameters();
   const TemplateArgumentList &TAList = TSpecial->getTemplateArgs();
diff --git a/test/CodeGenCXX/debug-info-template-member.cpp b/test/CodeGenCXX/debug-info-template-member.cpp
index db6006cab8..3d5b04d164 100644
--- a/test/CodeGenCXX/debug-info-template-member.cpp
+++ b/test/CodeGenCXX/debug-info-template-member.cpp
@@ -30,7 +30,7 @@ inline int add3(int x) {
 // CHECK: {{![0-9]+}} = distinct !DIGlobalVariable(
 // CHECK-SAME: name: "var"
 // CHECK-SAME: templateParams: {{![0-9]+}}
-// CHECK: !DITemplateTypeParameter(name: "P", type: {{![0-9]+}})
+// CHECK: !DITemplateTypeParameter(name: "T", type: {{![0-9]+}})
 // CHECK: {{![0-9]+}} = distinct !DIGlobalVariable(
 // CHECK-SAME: name: "varray"
 // CHECK-SAME: templateParams: {{![0-9]+}}
diff --git a/test/CodeGenCXX/debug-info-var-template-partial.cpp b/test/CodeGenCXX/debug-info-var-template-partial.cpp
new file mode 100644
index 0000000000..21ea03b8ee
--- /dev/null
+++ b/test/CodeGenCXX/debug-info-var-template-partial.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -emit-llvm -triple x86_64-linux-gnu %s -o - -debug-info-kind=limited | FileCheck %s
+
+template <typename LHS, typename RHS> constexpr bool is_same_v = false;
+template <typename T> constexpr bool is_same_v<T, T> = true;
+
+template constexpr bool is_same_v<int, int>;
+static_assert(is_same_v<int, int>, "should get partial spec");
+
+// Note that the template arguments for the instantiated variable use the
+// parameter names from the primary template. The partial specialization might
+// not have enough parameters.
+
+// CHECK: distinct !DIGlobalVariable(name: "is_same_v", linkageName: "_Z9is_same_vIiiE", {{.*}} templateParams: ![[PARAMS:[0-9]+]])
+// CHECK: ![[PARAMS]] = !{![[LHS:[0-9]+]], ![[RHS:[0-9]+]]}
+// CHECK: ![[LHS]] = !DITemplateTypeParameter(name: "LHS", type: ![[INT:[0-9]+]])
+// CHECK: ![[INT]] = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+// CHECK: ![[RHS]] = !DITemplateTypeParameter(name: "RHS", type: ![[INT]])