Perform trivial tail call optimization for callees with "C" ABI. These are done
even when -tailcallopt is not specified and it does not require changing ABI.
First case is the most trivial one. Perform tail call optimization when both
the caller and callee do not return values and when the callee does not take
any input arguments.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94664 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 6e64475..eb7f481 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -12,6 +12,7 @@
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "x86-isel"
#include "X86.h"
#include "X86InstrBuilder.h"
#include "X86ISelLowering.h"
@@ -39,6 +40,7 @@
#include "llvm/MC/MCSymbol.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/VectorExtras.h"
#include "llvm/Support/CommandLine.h"
@@ -48,6 +50,8 @@
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
+STATISTIC(NumTailCalls, "Number of tail calls");
+
static cl::opt<bool>
DisableMMX("disable-mmx", cl::Hidden, cl::desc("Disable use of MMX"));
@@ -1788,7 +1792,7 @@
if (isTailCall)
// Check if it's really possible to do a tail call.
isTailCall = IsEligibleForTailCallOptimization(Callee, CallConv, isVarArg,
- Ins, DAG);
+ Outs, Ins, DAG);
assert(!(isVarArg && CallConv == CallingConv::Fast) &&
"Var args not supported with calling convention fastcc");
@@ -1806,6 +1810,8 @@
int FPDiff = 0;
if (isTailCall) {
+ ++NumTailCalls;
+
// Lower arguments at fp - stackoffset + fpdiff.
unsigned NumBytesCallerPushed =
MF.getInfo<X86MachineFunctionInfo>()->getBytesToPopOnReturn();
@@ -2237,11 +2243,29 @@
X86TargetLowering::IsEligibleForTailCallOptimization(SDValue Callee,
CallingConv::ID CalleeCC,
bool isVarArg,
- const SmallVectorImpl<ISD::InputArg> &Ins,
+ const SmallVectorImpl<ISD::OutputArg> &Outs,
+ const SmallVectorImpl<ISD::InputArg> &Ins,
SelectionDAG& DAG) const {
- if (CalleeCC == CallingConv::Fast &&
- DAG.getMachineFunction().getFunction()->getCallingConv() == CalleeCC)
+ // If -tailcallopt is specified, make fastcc functions tail-callable.
+ const Function *F = DAG.getMachineFunction().getFunction();
+ if (PerformTailCallOpt &&
+ CalleeCC == CallingConv::Fast && F->getCallingConv() == CalleeCC)
return true;
+
+ if (CalleeCC != CallingConv::Fast &&
+ CalleeCC != CallingConv::C)
+ return false;
+
+ // Look for obvious safe cases to perform tail call optimization.
+ // For now, only consider callees which take no arguments and no return
+ // values.
+ if (!Outs.empty())
+ return false;
+
+ if (Ins.empty())
+ // If the caller does not return a value, then this is obviously safe.
+ return F->getReturnType()->isVoidTy();
+
return false;
}
diff --git a/lib/Target/X86/X86ISelLowering.h b/lib/Target/X86/X86ISelLowering.h
index 0642b39..193ef05 100644
--- a/lib/Target/X86/X86ISelLowering.h
+++ b/lib/Target/X86/X86ISelLowering.h
@@ -630,7 +630,8 @@
bool IsEligibleForTailCallOptimization(SDValue Callee,
CallingConv::ID CalleeCC,
bool isVarArg,
- const SmallVectorImpl<ISD::InputArg> &Ins,
+ const SmallVectorImpl<ISD::OutputArg> &Outs,
+ const SmallVectorImpl<ISD::InputArg> &Ins,
SelectionDAG& DAG) const;
bool IsCalleePop(bool isVarArg, CallingConv::ID CallConv);
SDValue EmitTailCallLoadRetAddr(SelectionDAG &DAG, SDValue &OutRetAddr,
diff --git a/test/CodeGen/X86/pic.ll b/test/CodeGen/X86/pic.ll
index e886ba0..d3c28a0 100644
--- a/test/CodeGen/X86/pic.ll
+++ b/test/CodeGen/X86/pic.ll
@@ -190,7 +190,7 @@
; LINUX: .L8$pb:
; LINUX: addl $_GLOBAL_OFFSET_TABLE_+(.Lpicbaseref8-.L8$pb),
; LINUX: addl .LJTI8_0@GOTOFF(
-; LINUX: jmpl *%ecx
+; LINUX: jmpl *
; LINUX: .LJTI8_0:
; LINUX: .long .LBB8_2@GOTOFF
diff --git a/test/CodeGen/X86/tailcall1.ll b/test/CodeGen/X86/tailcall1.ll
index 42f8cdd..96c4cad 100644
--- a/test/CodeGen/X86/tailcall1.ll
+++ b/test/CodeGen/X86/tailcall1.ll
@@ -4,8 +4,8 @@
define fastcc i32 @tailcaller(i32 %in1, i32 %in2) nounwind {
entry:
- %tmp11 = tail call fastcc i32 @tailcallee(i32 %in1, i32 %in2, i32 %in1, i32 %in2)
- ret i32 %tmp11
+ %tmp11 = tail call fastcc i32 @tailcallee(i32 %in1, i32 %in2, i32 %in1, i32 %in2)
+ ret i32 %tmp11
}
declare fastcc i8* @alias_callee()
diff --git a/test/CodeGen/X86/tailcall2.ll b/test/CodeGen/X86/tailcall2.ll
new file mode 100644
index 0000000..f1eb152
--- /dev/null
+++ b/test/CodeGen/X86/tailcall2.ll
@@ -0,0 +1,12 @@
+; RUN: llc < %s -march=x86 -asm-verbose=false | FileCheck %s
+; RUN: llc < %s -march=x86-64 -asm-verbose=false | FileCheck %s
+
+define void @bar(i32 %x) nounwind ssp {
+entry:
+; CHECK: bar:
+; CHECK: jmp _foo
+ tail call void @foo() nounwind
+ ret void
+}
+
+declare void @foo()