Fix PR1788 by taking the approach suggested by Richard Smith.

Thanks to him for his detailed analysis of the problem.

llvm-svn: 44162

1 files changed, 16 insertions, 11 deletions

diff --git a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
index 8dd09256136..3d345eefaa1 100644
--- a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -604,23 +604,28 @@ void DAE::RemoveDeadArgumentsFromFunction(Function *F) {
 }
 
 bool DAE::runOnModule(Module &M) {
-  // First phase: loop through the module, determining which arguments are live.
-  // We assume all arguments are dead unless proven otherwise (allowing us to
-  // determine that dead arguments passed into recursive functions are dead).
-  //
-  DOUT << "DAE - Determining liveness\n";
+  bool Changed = false;
+  // First pass: Do a simple check to see if any functions can have their "..."
+  // removed.  We can do this if they never call va_start.  This loop cannot be
+  // fused with the next loop, because deleting a function invalidates
+  // information computed while surveying other functions.
+  DOUT << "DAE - Deleting dead varargs\n";
   for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
     Function &F = *I++;
     if (F.getFunctionType()->isVarArg())
-      if (DeleteDeadVarargs(F))
-        continue;
-      
-    SurveyFunction(F);
+      Changed |= DeleteDeadVarargs(F);
   }
+  
+  // Second phase:loop through the module, determining which arguments are live.
+  // We assume all arguments are dead unless proven otherwise (allowing us to
+  // determine that dead arguments passed into recursive functions are dead).
+  //
+  DOUT << "DAE - Determining liveness\n";
+  for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
+    SurveyFunction(*I);
 
   // Loop over the instructions to inspect, propagating liveness among arguments
   // and return values which are MaybeLive.
-
   while (!InstructionsToInspect.empty()) {
     Instruction *I = InstructionsToInspect.back();
     InstructionsToInspect.pop_back();
@@ -680,7 +685,7 @@ bool DAE::runOnModule(Module &M) {
   // to do.
   if (MaybeLiveArguments.empty() && DeadArguments.empty() &&
       MaybeLiveRetVal.empty() && DeadRetVal.empty())
-    return false;
+    return Changed;
 
   // Otherwise, compact into one set, and start eliminating the arguments from
   // the functions.