From e1478f87afcc458fb1b080cf187550255fc0d470 Mon Sep 17 00:00:00 2001
From: Hans Wennborg <hans@hanshq.net>
Date: Tue, 1 Sep 2015 18:06:46 +0000
Subject: [PATCH] DeadArgElim: don't eliminate arguments from naked functions

Differential Revision: http://reviews.llvm.org/D12534

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@246564 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../IPO/DeadArgumentElimination.cpp           | 21 +++++++++++++
 .../Transforms/DeadArgElim/naked_functions.ll | 31 +++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 test/Transforms/DeadArgElim/naked_functions.ll

diff --git a/lib/Transforms/IPO/DeadArgumentElimination.cpp b/lib/Transforms/IPO/DeadArgumentElimination.cpp
index d0447640259..64c5ab9cb1b 100644
--- a/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -198,6 +198,13 @@ bool DAE::DeleteDeadVarargs(Function &Fn) {
   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) {
@@ -345,6 +352,12 @@ bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
   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;
 
@@ -543,6 +556,14 @@ void DAE::SurveyFunction(const Function &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;
diff --git a/test/Transforms/DeadArgElim/naked_functions.ll b/test/Transforms/DeadArgElim/naked_functions.ll
new file mode 100644
index 00000000000..b7955a10127
--- /dev/null
+++ b/test/Transforms/DeadArgElim/naked_functions.ll
@@ -0,0 +1,31 @@
+; 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 }
-- 
2.34.1