Move isInTailCallPosition out of SelectionDAGBuilder, as it isn't

SelectionDAG-specific.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101801 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 95 insertions, 86 deletions

diff --git a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index ccccc2a..10b0ee4 100644
--- a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
@@ -448,3 +448,88 @@ ISD::CondCode llvm::getICmpCondCode(ICmpInst::Predicate Pred) {
     return ISD::SETNE;
   }
 }
+
+/// Test if the given instruction is in a position to be optimized
+/// with a tail-call. This roughly means that it's in a block with
+/// a return and there's nothing that needs to be scheduled
+/// between it and the return.
+///
+/// This function only tests target-independent requirements.
+bool llvm::isInTailCallPosition(ImmutableCallSite CS, Attributes CalleeRetAttr,
+                                const TargetLowering &TLI) {
+  const Instruction *I = CS.getInstruction();
+  const BasicBlock *ExitBB = I->getParent();
+  const TerminatorInst *Term = ExitBB->getTerminator();
+  const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
+  const Function *F = ExitBB->getParent();
+
+  // The block must end in a return statement or unreachable.
+  //
+  // FIXME: Decline tailcall if it's not guaranteed and if the block ends in
+  // an unreachable, for now. The way tailcall optimization is currently
+  // implemented means it will add an epilogue followed by a jump. That is
+  // not profitable. Also, if the callee is a special function (e.g.
+  // longjmp on x86), it can end up causing miscompilation that has not
+  // been fully understood.
+  if (!Ret &&
+      (!GuaranteedTailCallOpt || !isa<UnreachableInst>(Term))) return false;
+
+  // If I will have a chain, make sure no other instruction that will have a
+  // chain interposes between I and the return.
+  if (I->mayHaveSideEffects() || I->mayReadFromMemory() ||
+      !I->isSafeToSpeculativelyExecute())
+    for (BasicBlock::const_iterator BBI = prior(prior(ExitBB->end())); ;
+         --BBI) {
+      if (&*BBI == I)
+        break;
+      // Debug info intrinsics do not get in the way of tail call optimization.
+      if (isa<DbgInfoIntrinsic>(BBI))
+        continue;
+      if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
+          !BBI->isSafeToSpeculativelyExecute())
+        return false;
+    }
+
+  // If the block ends with a void return or unreachable, it doesn't matter
+  // what the call's return type is.
+  if (!Ret || Ret->getNumOperands() == 0) return true;
+
+  // If the return value is undef, it doesn't matter what the call's
+  // return type is.
+  if (isa<UndefValue>(Ret->getOperand(0))) return true;
+
+  // Conservatively require the attributes of the call to match those of
+  // the return. Ignore noalias because it doesn't affect the call sequence.
+  unsigned CallerRetAttr = F->getAttributes().getRetAttributes();
+  if ((CalleeRetAttr ^ CallerRetAttr) & ~Attribute::NoAlias)
+    return false;
+
+  // It's not safe to eliminate the sign / zero extension of the return value.
+  if ((CallerRetAttr & Attribute::ZExt) || (CallerRetAttr & Attribute::SExt))
+    return false;
+
+  // Otherwise, make sure the unmodified return value of I is the return value.
+  for (const Instruction *U = dyn_cast<Instruction>(Ret->getOperand(0)); ;
+       U = dyn_cast<Instruction>(U->getOperand(0))) {
+    if (!U)
+      return false;
+    if (!U->hasOneUse())
+      return false;
+    if (U == I)
+      break;
+    // Check for a truly no-op truncate.
+    if (isa<TruncInst>(U) &&
+        TLI.isTruncateFree(U->getOperand(0)->getType(), U->getType()))
+      continue;
+    // Check for a truly no-op bitcast.
+    if (isa<BitCastInst>(U) &&
+        (U->getOperand(0)->getType() == U->getType() ||
+         (U->getOperand(0)->getType()->isPointerTy() &&
+          U->getType()->isPointerTy())))
+      continue;
+    // Otherwise it's not a true no-op.
+    return false;
+  }
+
+  return true;
+}
diff --git a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.h b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.h
index 34c8da6..0d9af1a 100644
--- a/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.h
+++ b/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.h
@@ -24,6 +24,7 @@
 #endif
 #include "llvm/CodeGen/ValueTypes.h"
 #include "llvm/CodeGen/ISDOpcodes.h"
+#include "llvm/Support/CallSite.h"
 #include <vector>
 
 namespace llvm {
@@ -166,6 +167,15 @@ ISD::CondCode getFCmpCondCode(FCmpInst::Predicate Pred);
 ///
 ISD::CondCode getICmpCondCode(ICmpInst::Predicate Pred);
 
+/// Test if the given instruction is in a position to be optimized
+/// with a tail-call. This roughly means that it's in a block with
+/// a return and there's nothing that needs to be scheduled
+/// between it and the return.
+///
+/// This function only tests target-independent requirements.
+bool isInTailCallPosition(ImmutableCallSite CS, Attributes CalleeRetAttr,
+                          const TargetLowering &TLI);
+
 } // end namespace llvm
 
 #endif
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index fea8377..9011610 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4190,92 +4190,6 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
   }
 }
 
-/// Test if the given instruction is in a position to be optimized
-/// with a tail-call. This roughly means that it's in a block with
-/// a return and there's nothing that needs to be scheduled
-/// between it and the return.
-///
-/// This function only tests target-independent requirements.
-static bool
-isInTailCallPosition(ImmutableCallSite CS, Attributes CalleeRetAttr,
-                     const TargetLowering &TLI) {
-  const Instruction *I = CS.getInstruction();
-  const BasicBlock *ExitBB = I->getParent();
-  const TerminatorInst *Term = ExitBB->getTerminator();
-  const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
-  const Function *F = ExitBB->getParent();
-
-  // The block must end in a return statement or unreachable.
-  //
-  // FIXME: Decline tailcall if it's not guaranteed and if the block ends in
-  // an unreachable, for now. The way tailcall optimization is currently
-  // implemented means it will add an epilogue followed by a jump. That is
-  // not profitable. Also, if the callee is a special function (e.g.
-  // longjmp on x86), it can end up causing miscompilation that has not
-  // been fully understood.
-  if (!Ret &&
-      (!GuaranteedTailCallOpt || !isa<UnreachableInst>(Term))) return false;
-
-  // If I will have a chain, make sure no other instruction that will have a
-  // chain interposes between I and the return.
-  if (I->mayHaveSideEffects() || I->mayReadFromMemory() ||
-      !I->isSafeToSpeculativelyExecute())
-    for (BasicBlock::const_iterator BBI = prior(prior(ExitBB->end())); ;
-         --BBI) {
-      if (&*BBI == I)
-        break;
-      // Debug info intrinsics do not get in the way of tail call optimization.
-      if (isa<DbgInfoIntrinsic>(BBI))
-        continue;
-      if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
-          !BBI->isSafeToSpeculativelyExecute())
-        return false;
-    }
-
-  // If the block ends with a void return or unreachable, it doesn't matter
-  // what the call's return type is.
-  if (!Ret || Ret->getNumOperands() == 0) return true;
-
-  // If the return value is undef, it doesn't matter what the call's
-  // return type is.
-  if (isa<UndefValue>(Ret->getOperand(0))) return true;
-
-  // Conservatively require the attributes of the call to match those of
-  // the return. Ignore noalias because it doesn't affect the call sequence.
-  unsigned CallerRetAttr = F->getAttributes().getRetAttributes();
-  if ((CalleeRetAttr ^ CallerRetAttr) & ~Attribute::NoAlias)
-    return false;
-
-  // It's not safe to eliminate the sign / zero extension of the return value.
-  if ((CallerRetAttr & Attribute::ZExt) || (CallerRetAttr & Attribute::SExt))
-    return false;
-
-  // Otherwise, make sure the unmodified return value of I is the return value.
-  for (const Instruction *U = dyn_cast<Instruction>(Ret->getOperand(0)); ;
-       U = dyn_cast<Instruction>(U->getOperand(0))) {
-    if (!U)
-      return false;
-    if (!U->hasOneUse())
-      return false;
-    if (U == I)
-      break;
-    // Check for a truly no-op truncate.
-    if (isa<TruncInst>(U) &&
-        TLI.isTruncateFree(U->getOperand(0)->getType(), U->getType()))
-      continue;
-    // Check for a truly no-op bitcast.
-    if (isa<BitCastInst>(U) &&
-        (U->getOperand(0)->getType() == U->getType() ||
-         (U->getOperand(0)->getType()->isPointerTy() &&
-          U->getType()->isPointerTy())))
-      continue;
-    // Otherwise it's not a true no-op.
-    return false;
-  }
-
-  return true;
-}
-
 void SelectionDAGBuilder::LowerCallTo(ImmutableCallSite CS, SDValue Callee,
                                       bool isTailCall,
                                       MachineBasicBlock *LandingPad) {