From 8ae03404a3a38e34474d29f20bf5cd6b7088ada8 Mon Sep 17 00:00:00 2001
From: Bill Wendling <isanbard@gmail.com>
Date: Thu, 21 Nov 2013 07:05:41 +0000
Subject: Merging r195318:
 ------------------------------------------------------------------------
 r195318 | void | 2013-11-20 23:04:30 -0800 (Wed, 20 Nov 2013) | 29 lines

The basic problem is that some mainstream programs cannot deal with the way
clang optimizes tail calls, as in this example:

int foo(void);
int bar(void) {
 return foo();
}

where the call is transformed to:

  calll .L0$pb
.L0$pb:
  popl  %eax
.Ltmp0:
  addl  $_GLOBAL_OFFSET_TABLE_+(.Ltmp0-.L0$pb), %eax
  movl  foo@GOT(%eax), %eax
  popl  %ebp
  jmpl  *%eax                   # TAILCALL

However, the GOT references must all be resolved at dlopen() time, and so this
approach cannot be used with lazy dynamic linking (e.g. using RTLD_LAZY), which
usually populates the PLT with stubs that perform the actual resolving.

This patch changes X86TargetLowering::LowerCall() to skip tail call
optimization, if the called function is a global or external symbol.

Patch by Dimitry Andric!

PR15086
------------------------------------------------------------------------


git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@195319 91177308-0d34-0410-b5e6-96231b3b80d8
---
 test/CodeGen/X86/tail-call-got.ll | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

(limited to 'test/CodeGen/X86/tail-call-got.ll')

diff --git a/test/CodeGen/X86/tail-call-got.ll b/test/CodeGen/X86/tail-call-got.ll
index 84d561dcd8..bdfdeb5987 100644
--- a/test/CodeGen/X86/tail-call-got.ll
+++ b/test/CodeGen/X86/tail-call-got.ll
@@ -5,8 +5,7 @@ target triple = "i386-unknown-freebsd9.0"
 
 define double @test1(double %x) nounwind readnone {
 ; CHECK-LABEL: test1:
-; CHECK: movl foo@GOT
-; CHECK-NEXT: jmpl
+; CHECK: calll foo@PLT
   %1 = tail call double @foo(double %x) nounwind readnone
   ret double %1
 }
@@ -15,8 +14,7 @@ declare double @foo(double) readnone
 
 define double @test2(double %x) nounwind readnone {
 ; CHECK-LABEL: test2:
-; CHECK: movl sin@GOT
-; CHECK-NEXT: jmpl
+; CHECK: calll sin@PLT
   %1 = tail call double @sin(double %x) nounwind readnone
   ret double %1
 }
-- 
cgit v1.2.3