From 7e48926daec357789a2ffc27c44a4ed4d789eab8 Mon Sep 17 00:00:00 2001
From: Tom Stellard <tstellar@redhat.com>
Date: Mon, 9 Apr 2018 22:47:00 +0000
Subject: Merging r326376:

------------------------------------------------------------------------
r326376 | jdevlieghere | 2018-02-28 14:28:44 -0800 (Wed, 28 Feb 2018) | 12 lines

[GlobalOpt] don't change CC of musttail calle(e|r)

When the function has musttail call - its cc is fixed to be equal to the
cc of the musttail callee. In such case (and in the case of the musttail
callee), GlobalOpt should not change the cc to fastcc as it will break
the invariant.

This fixes PR36546

Patch by: Fedor Indutny (indutny)

Differential revision: https://reviews.llvm.org/D43859
------------------------------------------------------------------------

git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_60@329634 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/IPO/GlobalOpt.cpp         | 25 ++++++++++++++++++++++-
 test/Transforms/GlobalOpt/musttail_cc.ll | 34 ++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 1 deletion(-)
 create mode 100644 test/Transforms/GlobalOpt/musttail_cc.ll

diff --git a/lib/Transforms/IPO/GlobalOpt.cpp b/lib/Transforms/IPO/GlobalOpt.cpp
index 4bb2984e3b4..e0bbf45d316 100644
--- a/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/lib/Transforms/IPO/GlobalOpt.cpp
@@ -2099,8 +2099,31 @@ static void RemoveNestAttribute(Function *F) {
 /// GHC, or anyregcc.
 static bool isProfitableToMakeFastCC(Function *F) {
   CallingConv::ID CC = F->getCallingConv();
+
   // FIXME: Is it worth transforming x86_stdcallcc and x86_fastcallcc?
-  return CC == CallingConv::C || CC == CallingConv::X86_ThisCall;
+  if (CC != CallingConv::C && CC != CallingConv::X86_ThisCall)
+    return false;
+
+  // FIXME: Change CC for the whole chain of musttail calls when possible.
+  //
+  // Can't change CC of the function that either has musttail calls, or is a
+  // musttail callee itself
+  for (User *U : F->users()) {
+    if (isa<BlockAddress>(U))
+      continue;
+    CallInst* CI = dyn_cast<CallInst>(U);
+    if (!CI)
+      continue;
+
+    if (CI->isMustTailCall())
+      return false;
+  }
+
+  for (BasicBlock &BB : *F)
+    if (BB.getTerminatingMustTailCall())
+      return false;
+
+  return true;
 }
 
 static bool
diff --git a/test/Transforms/GlobalOpt/musttail_cc.ll b/test/Transforms/GlobalOpt/musttail_cc.ll
new file mode 100644
index 00000000000..fc927ea91dd
--- /dev/null
+++ b/test/Transforms/GlobalOpt/musttail_cc.ll
@@ -0,0 +1,34 @@
+; RUN: opt < %s -globalopt -S | FileCheck %s
+; PR36546
+
+; Check that musttail callee preserves its calling convention
+
+define i32 @test(i32 %a) {
+  ; CHECK: %ca = musttail call i32 @foo(i32 %a)
+  %ca = musttail call i32 @foo(i32 %a)
+  ret i32 %ca
+}
+
+; CHECK-LABEL: define internal i32 @foo(i32 %a)
+define internal i32 @foo(i32 %a) {
+  ret i32 %a
+}
+
+; Check that musttail caller preserves its calling convention
+
+define i32 @test2(i32 %a) {
+  %ca = call i32 @foo1(i32 %a)
+  ret i32 %ca
+}
+
+; CHECK-LABEL: define internal i32 @foo1(i32 %a)
+define internal i32 @foo1(i32 %a) {
+  ; CHECK: %ca = musttail call i32 @foo2(i32 %a)
+  %ca = musttail call i32 @foo2(i32 %a)
+  ret i32 %ca
+}
+
+; CHECK-LABEL: define internal i32 @foo2(i32 %a)
+define internal i32 @foo2(i32 %a) {
+  ret i32 %a
+}
-- 
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