[PowerPC] Fix calls to non-function objects

Looking at r225438 inspired me to see how the PowerPC backend handled the
situation (calling a bitcasted TLS global), and it turns out we also produced
an error (cannot select ...). What it means to "call" something that is not a
function is implementation and platform specific, but in the name of doing
something (besides crashing), this makes sure we do what GCC does (treat all
such calls as calls through a function pointer -- meaning that the pointer is
assumed, as is the convention on PPC, to point to a function descriptor
structure holding the actual code address along with the function's TOC pointer
and environment pointer). As GCC does, we now do the same for calling regular
(non-TLS) non-function globals too.

I'm not sure whether this is the most useful way to define the behavior, but at
least we won't be alone.

llvm-svn: 225617

2 files changed, 91 insertions, 5 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index e93c7819b1a..30f08d050da 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -3573,6 +3573,20 @@ void PrepareTailCall(SelectionDAG &DAG, SDValue &InFlag, SDValue &Chain,
   InFlag = Chain.getValue(1);
 }
 
+// Is this global address that of a function that can be called by name? (as
+// opposed to something that must hold a descriptor for an indirect call).
+static bool isFunctionGlobalAddress(SDValue Callee) {
+  if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
+    if (Callee.getOpcode() == ISD::GlobalTLSAddress ||
+        Callee.getOpcode() == ISD::TargetGlobalTLSAddress)
+      return false;
+
+    return G->getGlobal()->getType()->getElementType()->isFunctionTy();
+  }
+
+  return false;
+}
+
 static
 unsigned PrepareCall(SelectionDAG &DAG, SDValue &Callee, SDValue &InFlag,
                      SDValue &Chain, SDLoc dl, int SPDiff, bool isTailCall,
@@ -3598,7 +3612,10 @@ unsigned PrepareCall(SelectionDAG &DAG, SDValue &Callee, SDValue &InFlag,
       needIndirectCall = false;
     }
 
-  if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
+  if (isFunctionGlobalAddress(Callee)) {
+    GlobalAddressSDNode *G = cast<GlobalAddressSDNode>(Callee);
+    // A call to a TLS address is actually an indirect call to a
+    // thread-specific pointer.
     unsigned OpFlags = 0;
     if ((DAG.getTarget().getRelocationModel() != Reloc::Static &&
          (Subtarget.getTargetTriple().isMacOSX() &&
@@ -4649,8 +4666,8 @@ PPCTargetLowering::LowerCall_64SVR4(SDValue Chain, SDValue Callee,
   // See PrepareCall() for more information about calls through function
   // pointers in the 64-bit SVR4 ABI.
   if (!isTailCall &&
-      !dyn_cast<GlobalAddressSDNode>(Callee) &&
-      !dyn_cast<ExternalSymbolSDNode>(Callee)) {
+      !isFunctionGlobalAddress(Callee) &&
+      !isa<ExternalSymbolSDNode>(Callee)) {
     // Load r2 into a virtual register and store it to the TOC save area.
     SDValue Val = DAG.getCopyFromReg(Chain, dl, PPC::X2, MVT::i64);
     // TOC save area offset.
@@ -5053,8 +5070,8 @@ PPCTargetLowering::LowerCall_Darwin(SDValue Chain, SDValue Callee,
   // not mean the MTCTR instruction must use R12; it's easier to model this as
   // an extra parameter, so do that.
   if (!isTailCall &&
-      !dyn_cast<GlobalAddressSDNode>(Callee) &&
-      !dyn_cast<ExternalSymbolSDNode>(Callee) &&
+      !isFunctionGlobalAddress(Callee) &&
+      !isa<ExternalSymbolSDNode>(Callee) &&
       !isBLACompatibleAddress(Callee, DAG))
     RegsToPass.push_back(std::make_pair((unsigned)(isPPC64 ? PPC::X12 :
                                                    PPC::R12), Callee));
diff --git a/llvm/test/CodeGen/PowerPC/ppc64-nonfunc-calls.ll b/llvm/test/CodeGen/PowerPC/ppc64-nonfunc-calls.ll
new file mode 100644
index 00000000000..9f56f0102b7
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/ppc64-nonfunc-calls.ll
@@ -0,0 +1,69 @@
+; RUN: llc -mcpu=ppc64 < %s | FileCheck %s
+target datalayout = "E-m:e-i64:64-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+%struct.cd = type { i64, i64, i64 }
+
+@something = global [33 x i8] c"this is not really code, but...\0A\00", align 1
+@tls_something = thread_local global %struct.cd zeroinitializer, align 8
+@extern_something = external global %struct.cd
+
+; Function Attrs: nounwind
+define void @foo() #0 {
+entry:
+  tail call void bitcast ([33 x i8]* @something to void ()*)() #0
+  ret void
+
+; CHECK-LABEL: @foo
+; CHECK-DAG: addis [[REG1:[0-9]+]], 2, something@toc@ha
+; CHECK-DAG: std 2, 40(1)
+; CHECK-DAG: addi [[REG3:[0-9]+]], [[REG1]], something@toc@l
+; CHECK-DAG: ld [[REG2:[0-9]+]], 0([[REG3]])
+; CHECK-DAG: ld 11, 16([[REG3]])
+; CHECK-DAG: ld 2, 8([[REG3]])
+; CHECK-DAG: mtctr [[REG2]]
+; CHECK: bctrl
+; CHECK: ld 2, 40(1)
+; CHECK: blr
+}
+
+; Function Attrs: nounwind
+define void @bar() #0 {
+entry:
+  tail call void bitcast (%struct.cd* @tls_something to void ()*)() #0
+  ret void
+
+; CHECK-LABEL: @bar
+; CHECK-DAG: addis [[REG1:[0-9]+]], 13, tls_something@tprel@ha
+; CHECK-DAG: std 2, 40(1)
+; CHECK-DAG: addi [[REG3:[0-9]+]], [[REG1]], tls_something@tprel@l
+; CHECK-DAG: ld [[REG2:[0-9]+]], 0([[REG3]])
+; CHECK-DAG: ld 11, 16([[REG3]])
+; CHECK-DAG: ld 2, 8([[REG3]])
+; CHECK-DAG: mtctr [[REG2]]
+; CHECK: bctrl
+; CHECK: ld 2, 40(1)
+; CHECK: blr
+}
+
+; Function Attrs: nounwind
+define void @ext() #0 {
+entry:
+  tail call void bitcast (%struct.cd* @extern_something to void ()*)() #0
+  ret void
+
+; CHECK-LABEL: @ext
+; CHECK-DAG: addis [[REG1:[0-9]+]], 2, [[NAME:[._A-Za-z0-9]+]]@toc@ha
+; CHECK-DAG: std 2, 40(1)
+; CHECK-DAG: ld [[REG3:[0-9]+]], [[NAME]]@toc@l(3)
+; CHECK-DAG: ld [[REG2:[0-9]+]], 0([[REG3]])
+; CHECK-DAG: ld 11, 16([[REG3]])
+; CHECK-DAG: ld 2, 8([[REG3]])
+; CHECK-DAG: mtctr [[REG2]]
+; CHECK: bctrl
+; CHECK: ld 2, 40(1)
+; CHECK: blr
+}
+
+attributes #0 = { nounwind }
+