Remove DisableTailCalls from TargetOptions and the code in resetTargetOptions

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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239427 91177308-0d34-0410-b5e6-96231b3b80d8

Author: ahatanaka

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);

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) &&

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();

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) {

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

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() &&

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

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)

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" }

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" }