From 21a9a98b77c48fb5084d3ef470083704d13c3929 Mon Sep 17 00:00:00 2001
From: Akira Hatanaka <ahatanaka@mips.com>
Date: Sat, 27 Oct 2012 00:56:56 +0000
Subject: [PATCH] [mips] Do not tail-call optimize vararg functions or
 functions with byval arguments.

This is rather conservative and should be fixed later to be more aggressive.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166851 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/Mips/MipsISelLowering.cpp | 14 +++----
 lib/Target/Mips/MipsISelLowering.h   |  3 +-
 test/CodeGen/Mips/tailcall.ll        | 58 ++++++++++++++++++++++++++++
 3 files changed, 66 insertions(+), 9 deletions(-)

diff --git a/lib/Target/Mips/MipsISelLowering.cpp b/lib/Target/Mips/MipsISelLowering.cpp
index 02674f5d050..94e18689b73 100644
--- a/lib/Target/Mips/MipsISelLowering.cpp
+++ b/lib/Target/Mips/MipsISelLowering.cpp
@@ -2639,19 +2639,16 @@ static unsigned getNextIntArgReg(unsigned Reg) {
 /// IsEligibleForTailCallOptimization - Check whether the call is eligible
 /// for tail call optimization.
 bool MipsTargetLowering::
-IsEligibleForTailCallOptimization(CallingConv::ID CalleeCC,
+IsEligibleForTailCallOptimization(const MipsCC &MipsCCInfo, bool IsVarArg,
                                   unsigned NextStackOffset) const {
   if (!EnableMipsTailCalls)
     return false;
 
-  // Do not tail-call optimize if there is an argument passed on stack.
-  if (IsO32 && (CalleeCC != CallingConv::Fast)) {
-    if (NextStackOffset > 16)
-      return false;
-  } else if (NextStackOffset)
+  if (MipsCCInfo.hasByValArg() || IsVarArg)
     return false;
 
-  return true;
+  // Return true if no arguments are passed on stack.
+  return MipsCCInfo.reservedArgArea() == NextStackOffset;
 }
 
 /// LowerCall - functions arguments are copied from virtual regs to
@@ -2690,7 +2687,8 @@ MipsTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
 
   // Check if it's really possible to do a tail call.
   if (isTailCall)
-    isTailCall = IsEligibleForTailCallOptimization(CallConv, NextStackOffset);
+    isTailCall = IsEligibleForTailCallOptimization(MipsCCInfo, isVarArg,
+                                                   NextStackOffset);
 
   if (isTailCall)
     ++NumTailCalls;
diff --git a/lib/Target/Mips/MipsISelLowering.h b/lib/Target/Mips/MipsISelLowering.h
index 160349e4aaa..9e8c659829f 100644
--- a/lib/Target/Mips/MipsISelLowering.h
+++ b/lib/Target/Mips/MipsISelLowering.h
@@ -274,7 +274,8 @@ namespace llvm {
 
     /// IsEligibleForTailCallOptimization - Check whether the call is eligible
     /// for tail call optimization.
-    bool IsEligibleForTailCallOptimization(CallingConv::ID CalleeCC,
+    bool IsEligibleForTailCallOptimization(const MipsCC &MipsCCInfo,
+                                           bool IsVarArg,
                                            unsigned NextStackOffset) const;
 
     /// copyByValArg - Copy argument registers which were used to pass a byval
diff --git a/test/CodeGen/Mips/tailcall.ll b/test/CodeGen/Mips/tailcall.ll
index 4989636a20d..e82b1e3d510 100644
--- a/test/CodeGen/Mips/tailcall.ll
+++ b/test/CodeGen/Mips/tailcall.ll
@@ -66,9 +66,15 @@ declare i32 @callee4(i32, i32, i32, i32, i32, i32, i32, i32, i32)
 
 define i32 @caller5() nounwind readonly {
 entry:
+; PIC32: .ent caller5
 ; PIC32-NOT: jalr
+; PIC32: .end caller5
+; STATIC32: .ent caller5
 ; STATIC32-NOT: jal
+; STATIC32: .end caller5
+; N64: .ent caller5
 ; N64-NOT: jalr
+; N64: .end caller5
 
   %0 = load i32* @g0, align 4
   %1 = load i32* @g1, align 4
@@ -98,3 +104,55 @@ entry:
   ret i32 %add8
 }
 
+declare i32 @callee8(i32, ...)
+
+define i32 @caller8_0() nounwind {
+entry:
+  %call = tail call fastcc i32 @caller8_1()
+  ret i32 %call
+}
+
+define internal fastcc i32 @caller8_1() nounwind noinline {
+entry:
+; PIC32: .ent caller8_1
+; PIC32: jalr
+; PIC32: .end caller8_1
+; STATIC32: .ent caller8_1
+; STATIC32: jal
+; STATIC32: .end caller8_1
+; N64: .ent caller8_1
+; N64: jalr
+; N64: .end caller8_1
+
+  %call = tail call i32 (i32, ...)* @callee8(i32 2, i32 1) nounwind
+  ret i32 %call
+}
+
+%struct.S = type { [2 x i32] }
+
+@gs1 = external global %struct.S
+
+declare i32 @callee9(%struct.S* byval)
+
+define i32 @caller9_0() nounwind {
+entry:
+  %call = tail call fastcc i32 @caller9_1()
+  ret i32 %call
+}
+
+define internal fastcc i32 @caller9_1() nounwind noinline {
+entry:
+; PIC32: .ent caller9_1
+; PIC32: jalr
+; PIC32: .end caller9_1
+; STATIC32: .ent caller9_1
+; STATIC32: jal
+; STATIC32: .end caller9_1
+; N64: .ent caller9_1
+; N64: jalr
+; N64: .end caller9_1
+
+  %call = tail call i32 @callee9(%struct.S* byval @gs1) nounwind
+  ret i32 %call
+}
+