[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.

This reapplies r289902 with additional testcase upgrades.

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

llvm-svn: 289920

1 files changed, 7 insertions, 9 deletions

diff --git a/llvm/lib/IR/DebugInfo.cpp b/llvm/lib/IR/DebugInfo.cpp
index 7f91b49d828..6b9bc689a44 100644
--- a/llvm/lib/IR/DebugInfo.cpp
+++ b/llvm/lib/IR/DebugInfo.cpp
@@ -53,11 +53,12 @@ void DebugInfoFinder::reset() {
 void DebugInfoFinder::processModule(const Module &M) {
   for (auto *CU : M.debug_compile_units()) {
     addCompileUnit(CU);
-    for (auto *DIG : CU->getGlobalVariables()) {
-      if (addGlobalVariable(DIG)) {
-        processScope(DIG->getScope());
-        processType(DIG->getType().resolve());
-      }
+    for (auto DIG : CU->getGlobalVariables()) {
+      if (!addGlobalVariable(DIG))
+        continue;
+      auto *GV = DIG->getVariable();
+      processScope(GV->getScope());
+      processType(GV->getType().resolve());
     }
     for (auto *ET : CU->getEnumTypes())
       processType(ET);
@@ -206,10 +207,7 @@ bool DebugInfoFinder::addCompileUnit(DICompileUnit *CU) {
   return true;
 }
 
-bool DebugInfoFinder::addGlobalVariable(DIGlobalVariable *DIG) {
-  if (!DIG)
-    return false;
-
+bool DebugInfoFinder::addGlobalVariable(DIGlobalVariableExpression *DIG) {
   if (!NodesSeen.insert(DIG).second)
     return false;