From fad8d818dbd9784f58b04c0790435620226e0450 Mon Sep 17 00:00:00 2001
From: Reid Kleckner <reid@kleckner.net>
Date: Tue, 26 Aug 2014 00:59:51 +0000
Subject: [PATCH] musttail: Don't eliminate varargs packs if there is a
 forwarding call

Also clean up and beef up this grep test for the feature.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216425 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../IPO/DeadArgumentElimination.cpp           |  9 +++--
 test/Transforms/DeadArgElim/dead_vaargs.ll    | 36 +++++++++++++++----
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/lib/Transforms/IPO/DeadArgumentElimination.cpp b/lib/Transforms/IPO/DeadArgumentElimination.cpp
index ac3853dbd67..7b22e921814 100644
--- a/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/lib/Transforms/IPO/DeadArgumentElimination.cpp
@@ -199,10 +199,15 @@ bool DAE::DeleteDeadVarargs(Function &Fn) {
     return false;
 
   // Okay, we know we can transform this function if safe.  Scan its body
-  // looking for calls to llvm.vastart.
+  // 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) {
-      if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
+      CallInst *CI = dyn_cast<CallInst>(I);
+      if (!CI)
+        continue;
+      if (CI->isMustTailCall())
+        return false;
+      if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CI)) {
         if (II->getIntrinsicID() == Intrinsic::vastart)
           return false;
       }
diff --git a/test/Transforms/DeadArgElim/dead_vaargs.ll b/test/Transforms/DeadArgElim/dead_vaargs.ll
index db3135c8393..c8189c66b48 100644
--- a/test/Transforms/DeadArgElim/dead_vaargs.ll
+++ b/test/Transforms/DeadArgElim/dead_vaargs.ll
@@ -1,12 +1,36 @@
-; RUN: opt < %s -deadargelim -S | not grep 47 
-; RUN: opt < %s -deadargelim -S | not grep 1.0
+; RUN: opt < %s -deadargelim -S | FileCheck %s
 
 define i32 @bar(i32 %A) {
-        %tmp4 = tail call i32 (i32, ...)* @foo( i32 %A, i32 %A, i32 %A, i32 %A, i64 47, double 1.000000e+00 )   ; <i32> [#uses=1]
-        ret i32 %tmp4
+  call void (i32, ...)* @thunk(i32 %A, i64 47, double 1.000000e+00)
+  %a = call i32 (i32, ...)* @has_vastart(i32 %A, i64 47, double 1.000000e+00)
+  %b = call i32 (i32, ...)* @no_vastart( i32 %A, i32 %A, i32 %A, i32 %A, i64 47, double 1.000000e+00 )
+  %c = add i32 %a, %b
+  ret i32 %c
 }
+; CHECK-LABEL: define i32 @bar
+; CHECK: call void (i32, ...)* @thunk(i32 %A, i64 47, double 1.000000e+00)
+; CHECK: call i32 (i32, ...)* @has_vastart(i32 %A, i64 47, double 1.000000e+00)
+; CHECK: call i32 @no_vastart(i32 %A)
 
-define internal i32 @foo(i32 %X, ...) {
-        ret i32 %X
+declare void @thunk_target(i32 %X, ...)
+
+define internal void @thunk(i32 %X, ...) {
+  musttail call void(i32, ...)* @thunk_target(i32 %X, ...)
+  ret void
 }
+; CHECK-LABEL: define internal void @thunk(i32 %X, ...)
+; CHECK: musttail call void (i32, ...)* @thunk_target(i32 %X, ...)
 
+define internal i32 @has_vastart(i32 %X, ...) {
+  %valist = alloca i8
+  call void @llvm.va_start(i8* %valist)
+  ret i32 %X
+}
+; CHECK-LABEL: define internal i32 @has_vastart(i32 %X, ...)
+
+declare void @llvm.va_start(i8*)
+
+define internal i32 @no_vastart(i32 %X, ...) {
+  ret i32 %X
+}
+; CHECK-LABEL: define internal i32 @no_vastart(i32 %X)