Add 'musttail' marker to call instructions

This is similar to the 'tail' marker, except that it guarantees that
tail call optimization will occur.  It also comes with convervative IR
verification rules that ensure that tail call optimization is possible.

Reviewers: nicholas

Differential Revision: http://llvm-reviews.chandlerc.com/D3240

llvm-svn: 207143

6 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index 3e40f76bd2b..b1c31aa37f3 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -1524,6 +1524,10 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
                     IsVarArg, IsStructRet, MF.getFunction()->hasStructRetAttr(),
                                                    Outs, OutVals, Ins, DAG);
 
+    if (!IsTailCall && CLI.CS && CLI.CS->isMustTailCall())
+      report_fatal_error("failed to perform tail call elimination on a call "
+                         "site marked musttail");
+
     // A sibling call is one where we're under the usual C ABI and not planning
     // to change that but can still do a tail call:
     if (!TailCallOpt && IsTailCall)
diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 0a64d991c06..77d8f2109de 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -1400,6 +1400,9 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
     isTailCall = IsEligibleForTailCallOptimization(Callee, CallConv,
                     isVarArg, isStructRet, MF.getFunction()->hasStructRetAttr(),
                                                    Outs, OutVals, Ins, DAG);
+    if (!isTailCall && CLI.CS && CLI.CS->isMustTailCall())
+      report_fatal_error("failed to perform tail call elimination on a call "
+                         "site marked musttail");
     // We don't support GuaranteedTailCallOpt for ARM, only automatically
     // detected sibcalls.
     if (isTailCall) {
diff --git a/llvm/lib/Target/ARM64/ARM64ISelLowering.cpp b/llvm/lib/Target/ARM64/ARM64ISelLowering.cpp
index 154306c02be..58e425938e1 100644
--- a/llvm/lib/Target/ARM64/ARM64ISelLowering.cpp
+++ b/llvm/lib/Target/ARM64/ARM64ISelLowering.cpp
@@ -1957,6 +1957,9 @@ SDValue ARM64TargetLowering::LowerCall(CallLoweringInfo &CLI,
     IsTailCall = isEligibleForTailCallOptimization(
         Callee, CallConv, IsVarArg, IsStructRet,
         MF.getFunction()->hasStructRetAttr(), Outs, OutVals, Ins, DAG);
+    if (!IsTailCall && CLI.CS && CLI.CS->isMustTailCall())
+      report_fatal_error("failed to perform tail call elimination on a call "
+                         "site marked musttail");
     // We don't support GuaranteedTailCallOpt, only automatically
     // detected sibcalls.
     // FIXME: Re-evaluate. Is this true? Should it be true?
diff --git a/llvm/lib/Target/Mips/MipsISelLowering.cpp b/llvm/lib/Target/Mips/MipsISelLowering.cpp
index e7f4ee5526b..2f19701c69c 100644
--- a/llvm/lib/Target/Mips/MipsISelLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsISelLowering.cpp
@@ -2339,6 +2339,10 @@ MipsTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
       isEligibleForTailCallOptimization(MipsCCInfo, NextStackOffset,
                                         *MF.getInfo<MipsFunctionInfo>());
 
+  if (!IsTailCall && CLI.CS && CLI.CS->isMustTailCall())
+    report_fatal_error("failed to perform tail call elimination on a call "
+                       "site marked musttail");
+
   if (IsTailCall)
     ++NumTailCalls;
 
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 0c0ce5ac508..fce7d2fbea2 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -3720,6 +3720,10 @@ PPCTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
     isTailCall = IsEligibleForTailCallOptimization(Callee, CallConv, isVarArg,
                                                    Ins, DAG);
 
+  if (!isTailCall && CLI.CS && CLI.CS->isMustTailCall())
+    report_fatal_error("failed to perform tail call elimination on a call "
+                       "site marked musttail");
+
   if (PPCSubTarget.isSVR4ABI()) {
     if (PPCSubTarget.isPPC64())
       return LowerCall_64SVR4(Chain, Callee, CallConv, isVarArg,
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 936699e9b59..8800bff87f8 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -2544,6 +2544,10 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
                     MF.getFunction()->hasStructRetAttr(), CLI.RetTy,
                     Outs, OutVals, Ins, DAG);
 
+    if (!isTailCall && CLI.CS && CLI.CS->isMustTailCall())
+      report_fatal_error("failed to perform tail call elimination on a call "
+                         "site marked musttail");
+
     // Sibcalls are automatically detected tailcalls which do not require
     // ABI changes.
     if (!MF.getTarget().Options.GuaranteedTailCallOpt && isTailCall)