[IR] Remove the DIExpression field from DIGlobalVariable.

This patch implements PR31013 by introducing a
DIGlobalVariableExpression that holds a pair of DIGlobalVariable and
DIExpression.

Currently, DIGlobalVariables holds a DIExpression. This is not the
best way to model this:

(1) The DIGlobalVariable should describe the source level variable,
    not how to get to its location.

(2) It makes it unsafe/hard to update the expressions when we call
    replaceExpression on the DIGLobalVariable.

(3) It makes it impossible to represent a global variable that is in
    more than one location (e.g., a variable with multiple
    DW_OP_LLVM_fragment-s).  We also moved away from attaching the
    DIExpression to DILocalVariable for the same reasons.

<rdar://problem/29250149>
https://llvm.org/bugs/show_bug.cgi?id=31013
Differential Revision: https://reviews.llvm.org/D26769

llvm-svn: 289902

1 files changed, 36 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index f83a340219d..e6f5590164d 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -464,6 +464,26 @@ void DwarfDebug::constructAndAddImportedEntityDIE(DwarfCompileUnit &TheCU,
     D->addChild(TheCU.constructImportedEntityDIE(N));
 }
 
+/// Sort and unique GVEs by comparing their fragment offset.
+static SmallVectorImpl<DwarfCompileUnit::GlobalExpr> &
+sortGlobalExprs(SmallVectorImpl<DwarfCompileUnit::GlobalExpr> &GVEs) {
+  std::sort(GVEs.begin(), GVEs.end(),
+            [](DwarfCompileUnit::GlobalExpr A, DwarfCompileUnit::GlobalExpr B) {
+              if (A.Expr != B.Expr && A.Expr && B.Expr &&
+                  A.Expr->isFragment() && B.Expr->isFragment())
+                return A.Expr->getFragmentOffsetInBits() <
+                       B.Expr->getFragmentOffsetInBits();
+              return false;
+            });
+  GVEs.erase(std::unique(GVEs.begin(), GVEs.end(),
+                         [](DwarfCompileUnit::GlobalExpr A,
+                            DwarfCompileUnit::GlobalExpr B) {
+                           return A.Expr == B.Expr;
+                         }),
+             GVEs.end());
+  return GVEs;
+}
+
 // Emit all Dwarf sections that should come prior to the content. Create
 // global DIEs and emit initial debug info sections. This is invoked by
 // the target AsmPrinter.
@@ -480,21 +500,30 @@ void DwarfDebug::beginModule() {
   // Tell MMI whether we have debug info.
   MMI->setDebugInfoAvailability(NumDebugCUs > 0);
   SingleCU = NumDebugCUs == 1;
-
-  DenseMap<DIGlobalVariable *, const GlobalVariable *> GVMap;
+  DenseMap<DIGlobalVariable *, SmallVector<DwarfCompileUnit::GlobalExpr, 1>>
+      GVMap;
   for (const GlobalVariable &Global : M->globals()) {
-    SmallVector<DIGlobalVariable *, 1> GVs;
+    SmallVector<DIGlobalVariableExpression *, 1> GVs;
     Global.getDebugInfo(GVs);
-    for (auto &GV : GVs)
-      GVMap[GV] = &Global;
+    for (auto *GVE : GVs)
+      GVMap[GVE->getVariable()].push_back({&Global, GVE->getExpression()});
   }
 
   for (DICompileUnit *CUNode : M->debug_compile_units()) {
     DwarfCompileUnit &CU = constructDwarfCompileUnit(CUNode);
     for (auto *IE : CUNode->getImportedEntities())
       CU.addImportedEntity(IE);
-    for (auto *GV : CUNode->getGlobalVariables())
-      CU.getOrCreateGlobalVariableDIE(GV, GVMap.lookup(GV));
+
+    // Global Variables.
+    for (auto *GVE : CUNode->getGlobalVariables())
+      GVMap[GVE->getVariable()].push_back({nullptr, GVE->getExpression()});
+    DenseSet<DIGlobalVariable *> Processed;
+    for (auto *GVE : CUNode->getGlobalVariables()) {
+      DIGlobalVariable *GV = GVE->getVariable();
+      if (Processed.insert(GV).second)
+        CU.getOrCreateGlobalVariableDIE(GV, sortGlobalExprs(GVMap[GV]));
+    }
+
     for (auto *Ty : CUNode->getEnumTypes()) {
       // The enum types array by design contains pointers to
       // MDNodes rather than DIRefs. Unique them here.