Remove DisableTailCalls from TargetOptions and the code in resetTarge…

…tOptions

that was resetting it.

Remove the uses of DisableTailCalls in subclasses of TargetLowering and use
the value of function attribute "disable-tail-calls" instead. Also,
unconditionally add pass TailCallElim to the pipeline and check the function
attribute at the start of runOnFunction to disable the pass on a per-function
basis. 
 
This is part of the work to remove TargetMachine::resetTargetOptions, and since
DisableTailCalls was the last non-fast-math option that was being reset in that
function, we should be able to remove the function entirely after the work to
propagate IR-level fast-math flags to DAG nodes is completed.

Out-of-tree users should remove the uses of DisableTailCalls and make changes
to attach attribute "disable-tail-calls"="true" or "false" to the functions in
the IR.

rdar://problem/13752163

Differential Revision: http://reviews.llvm.org/D10099

llvm-svn: 239427

llvm/include/llvm/CodeGen/CommandFlags.h

@@ -16,6 +16,7 @@
 #ifndef LLVM_CODEGEN_COMMANDFLAGS_H
 #define LLVM_CODEGEN_COMMANDFLAGS_H
 
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/IR/Module.h"
 #include "llvm/MC/MCTargetOptionsCommandFlags.h"
 #include "llvm//MC/SubtargetFeature.h"
@@ -247,7 +248,6 @@ static inline TargetOptions InitTargetOptionsFromCodeGenFlags() {
     Options.FloatABIType = FloatABIForCalls;
   Options.NoZerosInBSS = DontPlaceZerosInBSS;
   Options.GuaranteedTailCallOpt = EnableGuaranteedTailCallOpt;
-  Options.DisableTailCalls = DisableTailCalls;
   Options.StackAlignmentOverride = OverrideStackAlignment;
   Options.TrapFuncName = TrapFuncName;
   Options.PositionIndependentExecutable = EnablePIE;
@@ -315,6 +315,11 @@ static inline void setFunctionAttributes(StringRef CPU, StringRef Features,
                                        "no-frame-pointer-elim",
                                        DisableFPElim ? "true" : "false");
 
+    if (DisableTailCalls.getNumOccurrences() > 0)
+      NewAttrs = NewAttrs.addAttribute(Ctx, AttributeSet::FunctionIndex,
+                                       "disable-tail-calls",
+                                       toStringRef(DisableTailCalls));
+
     // Let NewAttrs override Attrs.
     NewAttrs = Attrs.addAttributes(Ctx, AttributeSet::FunctionIndex, NewAttrs);
     F.setAttributes(NewAttrs);

llvm/include/llvm/Target/TargetOptions.h

@@ -67,7 +67,7 @@ namespace llvm {
           HonorSignDependentRoundingFPMathOption(false),
           NoZerosInBSS(false),
           GuaranteedTailCallOpt(false),
-          DisableTailCalls(false), StackAlignmentOverride(0),
+          StackAlignmentOverride(0),
           EnableFastISel(false), PositionIndependentExecutable(false),
           UseInitArray(false), DisableIntegratedAS(false),
           CompressDebugSections(false), FunctionSections(false),
@@ -137,10 +137,6 @@ namespace llvm {
     /// as their parent function, etc.), using an alternate ABI if necessary.
     unsigned GuaranteedTailCallOpt : 1;
 
-    /// DisableTailCalls - This flag controls whether we will use tail calls.
-    /// Disabling them may be useful to maintain a correct call stack.
-    unsigned DisableTailCalls : 1;
-
     /// StackAlignmentOverride - Override default stack alignment for target.
     unsigned StackAlignmentOverride;
 
@@ -236,7 +232,6 @@ inline bool operator==(const TargetOptions &LHS,
     ARE_EQUAL(HonorSignDependentRoundingFPMathOption) &&
     ARE_EQUAL(NoZerosInBSS) &&
     ARE_EQUAL(GuaranteedTailCallOpt) &&
-    ARE_EQUAL(DisableTailCalls) &&
     ARE_EQUAL(StackAlignmentOverride) &&
     ARE_EQUAL(EnableFastISel) &&
     ARE_EQUAL(PositionIndependentExecutable) &&

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -1483,9 +1483,10 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   bool isStructRet    = (Outs.empty()) ? false : Outs[0].Flags.isSRet();
   bool isThisReturn   = false;
   bool isSibCall      = false;
+  auto Attr = MF.getFunction()->getFnAttribute("disable-tail-calls");
 
   // Disable tail calls if they're not supported.
-  if (!Subtarget->supportsTailCall() || MF.getTarget().Options.DisableTailCalls)
+  if (!Subtarget->supportsTailCall() || Attr.getValueAsString() == "true")
     isTailCall = false;
 
   if (isTailCall) {
@@ -2375,7 +2376,9 @@ bool ARMTargetLowering::mayBeEmittedAsTailCall(CallInst *CI) const {
   if (!Subtarget->supportsTailCall())
     return false;
 
-  if (!CI->isTailCall() || getTargetMachine().Options.DisableTailCalls)
+  auto Attr =
+      CI->getParent()->getParent()->getFnAttribute("disable-tail-calls");
+  if (!CI->isTailCall() || Attr.getValueAsString() == "true")
     return false;
 
   return !Subtarget->isThumb1Only();

llvm/lib/Target/Hexagon/HexagonISelLowering.cpp

@@ -397,7 +397,9 @@ HexagonTargetLowering::LowerReturn(SDValue Chain,
 
 bool HexagonTargetLowering::mayBeEmittedAsTailCall(CallInst *CI) const {
   // If either no tail call or told not to tail call at all, don't.
-  if (!CI->isTailCall() || HTM.Options.DisableTailCalls)
+  auto Attr =
+      CI->getParent()->getParent()->getFnAttribute("disable-tail-calls");
+  if (!CI->isTailCall() || Attr.getValueAsString() == "true")
     return false;
 
   return true;
@@ -486,7 +488,8 @@ HexagonTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   else
     CCInfo.AnalyzeCallOperands(Outs, CC_Hexagon);
 
-  if (DAG.getTarget().Options.DisableTailCalls)
+  auto Attr = MF.getFunction()->getFnAttribute("disable-tail-calls");
+  if (Attr.getValueAsString() == "true")
     isTailCall = false;
 
   if (isTailCall) {

llvm/lib/Target/TargetMachine.cpp

@@ -70,7 +70,6 @@ void TargetMachine::resetTargetOptions(const Function &F) const {
   RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
   RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
   RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
-  RESET_OPTION(DisableTailCalls, "disable-tail-calls");
 }
 
 /// getRelocationModel - Returns the code generation relocation model. The

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -2233,7 +2233,9 @@ static bool IsCCallConvention(CallingConv::ID CC) {
 }
 
 bool X86TargetLowering::mayBeEmittedAsTailCall(CallInst *CI) const {
-  if (!CI->isTailCall() || getTargetMachine().Options.DisableTailCalls)
+  auto Attr =
+      CI->getParent()->getParent()->getFnAttribute("disable-tail-calls");
+  if (!CI->isTailCall() || Attr.getValueAsString() == "true")
     return false;
 
   CallSite CS(CI);
@@ -2762,8 +2764,9 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   StructReturnType SR = callIsStructReturn(Outs);
   bool IsSibcall      = false;
   X86MachineFunctionInfo *X86Info = MF.getInfo<X86MachineFunctionInfo>();
+  auto Attr = MF.getFunction()->getFnAttribute("disable-tail-calls");
 
-  if (MF.getTarget().Options.DisableTailCalls)
+  if (Attr.getValueAsString() == "true")
     isTailCall = false;
 
   if (Subtarget->isPICStyleGOT() &&

llvm/lib/Transforms/IPO/PassManagerBuilder.cpp

@@ -94,7 +94,6 @@ PassManagerBuilder::PassManagerBuilder() {
     SizeLevel = 0;
     LibraryInfo = nullptr;
     Inliner = nullptr;
-    DisableTailCalls = false;
     DisableUnitAtATime = false;
     DisableUnrollLoops = false;
     BBVectorize = RunBBVectorization;
@@ -238,8 +237,7 @@ void PassManagerBuilder::populateModulePassManager(
   MPM.add(createInstructionCombiningPass());  // Combine silly seq's
   addExtensionsToPM(EP_Peephole, MPM);
 
-  if (!DisableTailCalls)
-    MPM.add(createTailCallEliminationPass()); // Eliminate tail calls
+  MPM.add(createTailCallEliminationPass()); // Eliminate tail calls
   MPM.add(createCFGSimplificationPass());     // Merge & remove BBs
   MPM.add(createReassociatePass());           // Reassociate expressions
   // Rotate Loop - disable header duplication at -Oz

llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp

@@ -158,6 +158,9 @@ bool TailCallElim::runOnFunction(Function &F) {
   if (skipOptnoneFunction(F))
     return false;
 
+  if (F.getFnAttribute("disable-tail-calls").getValueAsString() == "true")
+    return false;
+
   bool AllCallsAreTailCalls = false;
   bool Modified = markTails(F, AllCallsAreTailCalls);
   if (AllCallsAreTailCalls)

llvm/test/CodeGen/ARM/disable-tail-calls.ll

@@ -0,0 +1,40 @@
+; RUN: llc < %s -march arm | FileCheck %s --check-prefix=NO-OPTION
+; RUN: llc < %s -march arm -disable-tail-calls | FileCheck %s --check-prefix=DISABLE-TRUE
+; RUN: llc < %s -march arm -disable-tail-calls=false | FileCheck %s --check-prefix=DISABLE-FALSE
+
+; Check that command line option "-disable-tail-calls" overrides function
+; attribute "disable-tail-calls".
+
+; NO-OPTION-LABEL: {{\_?}}func_attr
+; NO-OPTION: bl {{\_?}}callee
+
+; DISABLE-FALSE-LABEL: {{\_?}}func_attr
+; DISABLE-FALSE: b {{\_?}}callee
+
+; DISABLE-TRUE-LABEL: {{\_?}}func_attr
+; DISABLE-TRUE: bl {{\_?}}callee
+
+define i32 @func_attr(i32 %a) #0 {
+entry:
+  %call = tail call i32 @callee(i32 %a)
+  ret i32 %call
+}
+
+; NO-OPTION-LABEL: {{\_?}}func_noattr
+; NO-OPTION: b {{\_?}}callee
+
+; DISABLE-FALSE-LABEL: {{\_?}}func_noattr
+; DISABLE-FALSE: b {{\_?}}callee
+
+; DISABLE-TRUE-LABEL: {{\_?}}func_noattr
+; DISABLE-TRUE: bl {{\_?}}callee
+
+define i32 @func_noattr(i32 %a) {
+entry:
+  %call = tail call i32 @callee(i32 %a)
+  ret i32 %call
+}
+
+declare i32 @callee(i32)
+
+attributes #0 = { "disable-tail-calls"="true" }

llvm/test/CodeGen/X86/disable-tail-calls.ll

@@ -0,0 +1,40 @@
+; RUN: llc < %s -march x86-64 | FileCheck %s --check-prefix=NO-OPTION
+; RUN: llc < %s -march x86-64 -disable-tail-calls | FileCheck %s --check-prefix=DISABLE-TRUE
+; RUN: llc < %s -march x86-64 -disable-tail-calls=false | FileCheck %s --check-prefix=DISABLE-FALSE
+
+; Check that command line option "-disable-tail-calls" overrides function
+; attribute "disable-tail-calls".
+
+; NO-OPTION-LABEL: {{\_?}}func_attr
+; NO-OPTION: callq {{\_?}}callee
+
+; DISABLE-FALSE-LABEL: {{\_?}}func_attr
+; DISABLE-FALSE: jmp {{\_?}}callee
+
+; DISABLE-TRUE-LABEL: {{\_?}}func_attr
+; DISABLE-TRUE: callq {{\_?}}callee
+
+define i32 @func_attr(i32 %a) #0 {
+entry:
+  %call = tail call i32 @callee(i32 %a)
+  ret i32 %call
+}
+
+; NO-OPTION-LABEL: {{\_?}}func_noattr
+; NO-OPTION: jmp {{\_?}}callee
+
+; DISABLE-FALSE-LABEL: {{\_?}}func_noattr
+; DISABLE-FALSE: jmp {{\_?}}callee
+
+; DISABLE-TRUE-LABEL: {{\_?}}func_noattr
+; DISABLE-TRUE: callq {{\_?}}callee
+
+define i32 @func_noattr(i32 %a) {
+entry:
+  %call = tail call i32 @callee(i32 %a)
+  ret i32 %call
+}
+
+declare i32 @callee(i32)
+
+attributes #0 = { "disable-tail-calls"="true" }