[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 and a change
to the Bitcode record for DIGlobalVariable, that makes upgrading the
old format unambiguous also for variables without DIExpressions.

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

llvm-svn: 290153

2 files changed, 11 insertions, 8 deletions

diff --git a/llvm/lib/Transforms/IPO/StripSymbols.cpp b/llvm/lib/Transforms/IPO/StripSymbols.cpp
index 5cb8ff56584..8f6f161428e 100644
--- a/llvm/lib/Transforms/IPO/StripSymbols.cpp
+++ b/llvm/lib/Transforms/IPO/StripSymbols.cpp
@@ -313,20 +313,23 @@ bool StripDeadDebugInfo::runOnModule(Module &M) {
   // replace the current list of potentially dead global variables/functions
   // with the live list.
   SmallVector<Metadata *, 64> LiveGlobalVariables;
-  DenseSet<const MDNode *> VisitedSet;
+  DenseSet<DIGlobalVariableExpression *> VisitedSet;
 
-  std::set<DIGlobalVariable *> LiveGVs;
+  std::set<DIGlobalVariableExpression *> LiveGVs;
   for (GlobalVariable &GV : M.globals()) {
-    SmallVector<DIGlobalVariable *, 1> DIs;
-    GV.getDebugInfo(DIs);
-    for (DIGlobalVariable *DI : DIs)
-      LiveGVs.insert(DI);
+    SmallVector<DIGlobalVariableExpression *, 1> GVEs;
+    GV.getDebugInfo(GVEs);
+    for (auto *GVE : GVEs)
+      LiveGVs.insert(GVE);
   }
 
   for (DICompileUnit *DIC : F.compile_units()) {
     // Create our live global variable list.
     bool GlobalVariableChange = false;
-    for (DIGlobalVariable *DIG : DIC->getGlobalVariables()) {
+    for (auto *DIG : DIC->getGlobalVariables()) {
+      if (DIG->getExpression() && DIG->getExpression()->isConstant())
+        LiveGVs.insert(DIG);
+
       // Make sure we only visit each global variable only once.
       if (!VisitedSet.insert(DIG).second)
         continue;
diff --git a/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
index acc13aaeaf4..6a7cb0e45c6 100644
--- a/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -1655,7 +1655,7 @@ bool AddressSanitizerModule::InstrumentGlobals(IRBuilder<> &IRB, Module &M) {
 
     // Transfer the debug info.  The payload starts at offset zero so we can
     // copy the debug info over as is.
-    SmallVector<DIGlobalVariable *, 1> GVs;
+    SmallVector<DIGlobalVariableExpression *, 1> GVs;
     G->getDebugInfo(GVs);
     for (auto *GV : GVs)
       NewGlobal->addDebugInfo(GV);