[PowerPC] Add support for -mlongcall

The "long call" option forces the use of the indirect calling sequence for all
calls (even those that don't really need it). GCC provides this option; This is
helpful, under certain circumstances, for building very-large binaries, and
some other specialized use cases.

Fixes PR19098.

llvm-svn: 280040

5 files changed, 41 insertions, 1 deletions

diff --git a/llvm/lib/Target/PowerPC/PPC.td b/llvm/lib/Target/PowerPC/PPC.td
index b40b530f4c5..ac1c3060046 100644
--- a/llvm/lib/Target/PowerPC/PPC.td
+++ b/llvm/lib/Target/PowerPC/PPC.td
@@ -136,6 +136,8 @@ def FeatureInvariantFunctionDescriptors :
   SubtargetFeature<"invariant-function-descriptors",
                    "HasInvariantFunctionDescriptors", "true",
                    "Assume function descriptors are invariant">;
+def FeatureLongCall : SubtargetFeature<"longcall", "UseLongCalls", "true",
+                                       "Always use indirect calls">;
 def FeatureHTM : SubtargetFeature<"htm", "HasHTM", "true",
                                   "Enable Hardware Transactional Memory instructions">;
 def FeatureMFTB   : SubtargetFeature<"", "FeatureMFTB", "true",
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index f895b06ac68..09887c3e4d1 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -4695,7 +4695,9 @@ PPCTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   ImmutableCallSite *CS                 = CLI.CS;
 
   if (isTailCall) {
-    if (Subtarget.isSVR4ABI() && Subtarget.isPPC64())
+    if (Subtarget.useLongCalls() && !(CS && CS->isMustTailCall()))
+      isTailCall = false;
+    else if (Subtarget.isSVR4ABI() && Subtarget.isPPC64())
       isTailCall =
         IsEligibleForTailCallOptimization_64SVR4(Callee, CallConv, CS,
                                                  isVarArg, Outs, Ins, DAG);
@@ -4725,6 +4727,13 @@ PPCTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
     report_fatal_error("failed to perform tail call elimination on a call "
                        "site marked musttail");
 
+  // When long calls (i.e. indirect calls) are always used, calls are always
+  // made via function pointer. If we have a function name, first translate it
+  // into a pointer.
+  if (Subtarget.useLongCalls() && isa<GlobalAddressSDNode>(Callee) &&
+      !isTailCall)
+    Callee = LowerGlobalAddress(Callee, DAG);
+
   if (Subtarget.isSVR4ABI()) {
     if (Subtarget.isPPC64())
       return LowerCall_64SVR4(Chain, Callee, CallConv, isVarArg,
diff --git a/llvm/lib/Target/PowerPC/PPCSubtarget.cpp b/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
index 603f0fccc7c..19570735295 100644
--- a/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
+++ b/llvm/lib/Target/PowerPC/PPCSubtarget.cpp
@@ -105,6 +105,7 @@ void PPCSubtarget::initializeEnvironment() {
   HasFusion = false;
   HasFloat128 = false;
   IsISA3_0 = false;
+  UseLongCalls = false;
 
   HasPOPCNTD = POPCNTD_Unavailable;
 }
diff --git a/llvm/lib/Target/PowerPC/PPCSubtarget.h b/llvm/lib/Target/PowerPC/PPCSubtarget.h
index 9fe286a3b7a..f58c7c10c8b 100644
--- a/llvm/lib/Target/PowerPC/PPCSubtarget.h
+++ b/llvm/lib/Target/PowerPC/PPCSubtarget.h
@@ -132,6 +132,7 @@ protected:
   bool HasFusion;
   bool HasFloat128;
   bool IsISA3_0;
+  bool UseLongCalls;
 
   POPCNTDKind HasPOPCNTD;
 
@@ -275,6 +276,7 @@ public:
   bool hasFusion() const { return HasFusion; }
   bool hasFloat128() const { return HasFloat128; }
   bool isISA3_0() const { return IsISA3_0; }
+  bool useLongCalls() const { return UseLongCalls; }
 
   POPCNTDKind hasPOPCNTD() const { return HasPOPCNTD; }
 
diff --git a/llvm/test/CodeGen/PowerPC/longcall.ll b/llvm/test/CodeGen/PowerPC/longcall.ll
new file mode 100644
index 00000000000..9645ca8d31f
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/longcall.ll
@@ -0,0 +1,26 @@
+; RUN: llc < %s | FileCheck %s
+target datalayout = "E-m:e-i64:64-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+; Function Attrs: nounwind
+define void @bar() local_unnamed_addr #0 {
+entry:
+  tail call void @foo() #1
+  ret void
+
+; CHECK-LABEL: @bar
+; CHECK: ld [[FD:[0-9]+]], .LC0@toc@l({{[0-9]+}})
+; CHECK: ld [[ADDR:[0-9]+]], 0([[FD]])
+; CHECK: mtctr [[ADDR]]
+; CHECK: bctrl
+; CHECK-NOT: bl foo
+; CHECK: blr
+}
+
+; CHECK: .tc foo
+
+declare void @foo() local_unnamed_addr
+
+attributes #0 = { nounwind "target-cpu"="ppc64" "target-features"="+longcall" }
+attributes #1 = { nounwind }
+