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 3d0f638c5eb0812337492406d0f71f9dd88608ca..6bddf46da1915fdf6bbb09ed6d1f85a7bf224de8 100644 (file)
--- 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 7c4ebc03d8b2c47f1e8bf1f8a164250c4bd13f47..85a6617bbf679706cedf2c120ba621b1b4cfb849 100644 (file)
--- 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 (file)
index 0000000..466c33d
--- /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
+