Fix PR26585 by improving the promotion of DBG_VALUEs to DW_AT_locations.
When a variable is described by a single DBG_VALUE instruction we can
often use a more efficient inline DW_AT_location instead of using a
location list.
This commit makes the heuristic that decides when to apply this
optimization stricter by also verifying that the DBG_VALUE is live at the
entry of the function (instead of just checking that it is valid until
the end of the function).
<rdar://problem/24611008>
llvm-svn: 262247
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 819ab9f..87e8866 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -935,6 +935,18 @@
return ConcreteVariables.back().get();
}
+// Determine whether this DBG_VALUE is valid at the beginning of the function.
+static bool validAtEntry(const MachineInstr *MInsn) {
+ auto MBB = MInsn->getParent();
+ // Is it in the entry basic block?
+ if (!MBB->pred_empty())
+ return false;
+ for (MachineBasicBlock::const_reverse_iterator I(MInsn); I != MBB->rend(); ++I)
+ if (!(I->isDebugValue() || I->getFlag(MachineInstr::FrameSetup)))
+ return false;
+ return true;
+}
+
// Find variables for each lexical scope.
void DwarfDebug::collectVariableInfo(DwarfCompileUnit &TheCU,
const DISubprogram *SP,
@@ -967,8 +979,11 @@
const MachineInstr *MInsn = Ranges.front().first;
assert(MInsn->isDebugValue() && "History must begin with debug value");
- // Check if the first DBG_VALUE is valid for the rest of the function.
- if (Ranges.size() == 1 && Ranges.front().second == nullptr) {
+ // Check if there is a single DBG_VALUE, valid throughout the function.
+ // A single constant is also considered valid for the entire function.
+ if (Ranges.size() == 1 &&
+ (MInsn->getOperand(0).isImm() ||
+ (validAtEntry(MInsn) && Ranges.front().second == nullptr))) {
RegVar->initializeDbgValue(MInsn);
continue;
}