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

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) &&