DeadArgElim: don't eliminate arguments from naked functions

[rnk]

lgtm

lib/Transforms/IPO/DeadArgumentElimination.cpp

 bool DAE::DeleteDeadVarargs(Function &Fn) {
   assert(Fn.getFunctionType()->isVarArg() && "Function isn't varargs!");
   if (Fn.isDeclaration() || !Fn.hasLocalLinkage()) return false;
 
   // Ensure that the function is only directly called.
   if (Fn.hasAddressTaken())
     return false;
 
+  // Don't touch naked functions. The assembly might be using an argument, or
+  // otherwise rely on the frame layout in a way that this analysis will not
+  // see.
+  if (Fn.hasFnAttribute(Attribute::Naked)) {
+    return false;
+  }
+
   // Okay, we know we can transform this function if safe.  Scan its body
   // looking for calls marked musttail or calls to llvm.vastart.
   for (Function::iterator BB = Fn.begin(), E = Fn.end(); BB != E; ++BB) {
     for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
       CallInst *CI = dyn_cast<CallInst>(I);
       if (!CI)
         continue;
       if (CI->isMustTailCall())
bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
   if (!Fn.isStrongDefinitionForLinker())
     return false;
 
   // Functions with local linkage should already have been handled, except the
   // fragile (variadic) ones which we can improve here.
   if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
     return false;
 
+  // Don't touch naked functions. The assembly might be using an argument, or
+  // otherwise rely on the frame layout in a way that this analysis will not
+  // see.
+  if (Fn.hasFnAttribute(Attribute::Naked))
+    return false;
+
   if (Fn.use_empty())
     return false;
 
   SmallVector<unsigned, 8> UnusedArgs;
   for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end(); 
        I != E; ++I) {
     Argument *Arg = I;
 

 void DAE::SurveyFunction(const Function &F) {
   // Functions with inalloca parameters are expecting args in a particular
   // register and memory layout.
   if (F.getAttributes().hasAttrSomewhere(Attribute::InAlloca)) {
     MarkLive(F);
     return;
   }
 
+  // Don't touch naked functions. The assembly might be using an argument, or
+  // otherwise rely on the frame layout in a way that this analysis will not
+  // see.
+  if (F.hasFnAttribute(Attribute::Naked)) {
+    MarkLive(F);
+    return;
+  }
+
   unsigned RetCount = NumRetVals(&F);
   // Assume all return values are dead
   typedef SmallVector<Liveness, 5> RetVals;
   RetVals RetValLiveness(RetCount, MaybeLive);
 
   typedef SmallVector<UseVector, 5> RetUses;
   // These vectors map each return value to the uses that make it MaybeLive, so
   // we can add those to the Uses map if the return value really turns out to be

test/Transforms/DeadArgElim/naked_functions.ll

+; RUN: opt -S -deadargelim %s | FileCheck %s
+
+; Don't eliminate dead arugments from naked functions.
+; CHECK: define internal i32 @naked(i32 %x)
+
+define internal i32 @naked(i32 %x) #0 {
+  tail call void asm sideeffect inteldialect "mov eax, [esp + $$4]\0A\09ret", "~{eax},~{dirflag},~{fpsr},~{flags}"()
+  unreachable
+}
+
+
+; Don't eliminate dead varargs from naked functions.
+; CHECK: define internal i32 @naked_va(i32 %x, ...)
+
+define internal i32 @naked_va(i32 %x, ...) #0 {
+  tail call void asm sideeffect inteldialect "mov eax, [esp + $$8]\0A\09ret", "~{eax},~{dirflag},~{fpsr},~{flags}"()
+  unreachable
+}
+
+define i32 @f(i32 %x, i32 %y) {
+  %r = call i32 @naked(i32 %x)
+  %s = call i32 (i32, ...) @naked_va(i32 %x, i32 %r)
+
+; Make sure the arguments are still there: not removed or replaced with undef.
+; CHECK: %r = call i32 @naked(i32 %x)
+; CHECK: %s = call i32 (i32, ...) @naked_va(i32 %x, i32 %r)
+
+  ret i32 %s
+}
+
+attributes #0 = { naked }