From: Saleem Abdulrasool <compnerd@compnerd.org>
Date: Sat, 3 Jan 2015 21:35:00 +0000 (+0000)
Subject: ARM: permit tail calls to weak externals on COFF
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=97f8f69a7fe4d28743c92bdb0daf169558a3e3ba;p=oota-llvm.git

ARM: permit tail calls to weak externals on COFF

Weak externals are resolved statically, so we can actually generate the tail
call on PE/COFF targets without breaking the requirements.  It is questionable
whether we want to propagate the current behaviour for MachO as the requirements
are part of the ARM ELF specifications, and it seems that prior to the SVN
r215890, we would have tail'ed the call.  For now, be conservative and only
permit it on PE/COFF where the call will always be fully resolved.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225119 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/AArch64/AArch64ISelLowering.cpp b/lib/Target/AArch64/AArch64ISelLowering.cpp
index 3d0f638c5eb..6bddf46da19 100644
--- a/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -2358,7 +2358,9 @@ bool AArch64TargetLowering::isEligibleForTailCallOptimization(
   // cannot rely on the linker replacing the tail call with a return.
   if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
     const GlobalValue *GV = G->getGlobal();
-    if (GV->hasExternalWeakLinkage())
+    const Triple TT(getTargetMachine().getTargetTriple());
+    if (GV->hasExternalWeakLinkage() &&
+        (!TT.isOSWindows() || TT.isOSBinFormatELF() || TT.isOSBinFormatMachO()))
       return false;
   }
 
diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 7c4ebc03d8b..85a6617bbf6 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -2026,7 +2026,9 @@ ARMTargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
   // cannot rely on the linker replacing the tail call with a return.
   if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
     const GlobalValue *GV = G->getGlobal();
-    if (GV->hasExternalWeakLinkage())
+    const Triple TT(getTargetMachine().getTargetTriple());
+    if (GV->hasExternalWeakLinkage() &&
+        (!TT.isOSWindows() || TT.isOSBinFormatELF() || TT.isOSBinFormatMachO()))
       return false;
   }
 
diff --git a/test/CodeGen/ARM/tail-call-weak.ll b/test/CodeGen/ARM/tail-call-weak.ll
new file mode 100644
index 00000000000..466c33d3878
--- /dev/null
+++ b/test/CodeGen/ARM/tail-call-weak.ll
@@ -0,0 +1,19 @@
+; RUN: llc -mtriple thumbv7-windows-coff -filetype asm -o - %s | FileCheck %s -check-prefix CHECK-COFF
+; RUN: llc -mtriple thumbv7-elf -filetype asm -o - %s | FileCheck %s -check-prefix CHECK-ELF
+; RUN: llc -mtriple thumbv7-macho -filetype asm -o - %s | FileCheck %s -check-prefix CHECK-MACHO
+
+declare i8* @f()
+declare extern_weak i8* @g(i8*)
+
+; weak symbol resolution occurs statically in PE/COFF, ensure that we permit
+; tail calls on weak externals when targeting a COFF environment.
+define void @test() {
+  %call = tail call i8* @f()
+  %call1 = tail call i8* @g(i8* %call)
+  ret void
+}
+
+; CHECK-COFF: b g
+; CHECK-ELF: bl g
+; CHECK-MACHO: blx _g
+