Debug info for variables whose type is shrinked to bool

This patch provides such debug information for integer
variables whose type is shrinked to bool by providing 
dwarf expression which returns either constant initial 
value or other value.

Patch by Nikola Prica.

Differential Revision: https://reviews.llvm.org/D35994

llvm-svn: 312318

1 files changed, 37 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
index ee8fdaebbda..8d4bde40968 100644
--- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -36,6 +36,7 @@
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/IR/ValueHandle.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -1603,12 +1604,47 @@ static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
   assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
          "No reason to shrink to bool!");
 
+  SmallVector<DIGlobalVariableExpression *, 1> GVs;
+  GV->getDebugInfo(GVs);
+
   // If initialized to zero and storing one into the global, we can use a cast
   // instead of a select to synthesize the desired value.
   bool IsOneZero = false;
-  if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
+  if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)){
     IsOneZero = InitVal->isNullValue() && CI->isOne();
 
+    ConstantInt *CIInit = dyn_cast<ConstantInt>(GV->getInitializer());
+    uint64_t ValInit = CIInit->getZExtValue();
+    uint64_t ValOther = CI->getZExtValue();
+    uint64_t ValMinus = ValOther - ValInit;
+
+    for(auto *GVe : GVs){
+      DIGlobalVariable *DGV = GVe->getVariable();
+      DIExpression *E = GVe->getExpression();
+
+      // val * (ValOther - ValInit) + ValInit:
+      // DW_OP_deref DW_OP_constu <ValMinus>
+      // DW_OP_mul DW_OP_constu <ValInit> DW_OP_plus DW_OP_stack_value
+      E = DIExpression::get(NewGV->getContext(),
+                           {dwarf::DW_OP_deref,
+                            dwarf::DW_OP_constu,
+                            ValMinus,
+                            dwarf::DW_OP_mul,
+                            dwarf::DW_OP_constu,
+                            ValInit,
+                            dwarf::DW_OP_plus,
+                            dwarf::DW_OP_stack_value});
+      DIGlobalVariableExpression *DGVE =
+        DIGlobalVariableExpression::get(NewGV->getContext(), DGV, E);
+      NewGV->addDebugInfo(DGVE);
+    }
+  } else {
+    // FIXME: This will only emit address for debugger on which will
+    // be written only 0 or 1.
+    for(auto *GV : GVs)
+      NewGV->addDebugInfo(GV);
+  }
+
   while (!GV->use_empty()) {
     Instruction *UI = cast<Instruction>(GV->user_back());
     if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {