swifterror: Don't compute swifterror vregs during instruction selection

The code used llvm basic block predecessors to decided where to insert phi
nodes. Instruction selection can and will liberally insert new machine basic
block predecessors. There is not a guaranteed one-to-one mapping from pred.
llvm basic blocks and machine basic blocks.

Therefore the current approach does not work as it assumes we can mark
predecessor machine basic block as needing a copy, and needs to know the set of
all predecessor machine basic blocks to decide when to insert phis.

Instead of computing the swifterror vregs as we select instructions, propagate
them at the end of instruction selection when the MBB CFG is complete.

When an instruction needs a swifterror vreg and we don't know the value yet,
generate a new vreg and remember this "upward exposed" use, and reconcile this
at the end of instruction selection.

This will only happen if the target supports promoting swifterror parameters to
registers and the swifterror attribute is used.

rdar://28300923

llvm-svn: 283617

1 files changed, 20 insertions, 12 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp b/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
index 87c968a85e9..3d27f5df205 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
@@ -596,18 +596,26 @@ void llvm::AddLandingPadInfo(const LandingPadInst &I, MachineModuleInfo &MMI,
   }
 }
 
-unsigned FunctionLoweringInfo::findSwiftErrorVReg(const MachineBasicBlock *MBB,
-                                                  const Value* Val) const {
-  // Find the index in SwiftErrorVals.
-  SwiftErrorValues::const_iterator I = find(SwiftErrorVals, Val);
-  assert(I != SwiftErrorVals.end() && "Can't find value in SwiftErrorVals");
-  return SwiftErrorMap.lookup(MBB)[I - SwiftErrorVals.begin()];
+unsigned
+FunctionLoweringInfo::getOrCreateSwiftErrorVReg(const MachineBasicBlock *MBB,
+                                                const Value *Val) {
+  auto Key = std::make_pair(MBB, Val);
+  auto It = SwiftErrorVRegDefMap.find(Key);
+  // If this is the first use of this swifterror value in this basic block,
+  // create a new virtual register.
+  // After we processed all basic blocks we will satisfy this "upwards exposed
+  // use" by inserting a copy or phi at the beginning of this block.
+  if (It == SwiftErrorVRegDefMap.end()) {
+    auto &DL = MF->getDataLayout();
+    const TargetRegisterClass *RC = TLI->getRegClassFor(TLI->getPointerTy(DL));
+    auto VReg = MF->getRegInfo().createVirtualRegister(RC);
+    SwiftErrorVRegDefMap[Key] = VReg;
+    SwiftErrorVRegUpwardsUse[Key] = VReg;
+    return VReg;
+  } else return It->second;
 }
 
-void FunctionLoweringInfo::setSwiftErrorVReg(const MachineBasicBlock *MBB,
-                                             const Value* Val, unsigned VReg) {
-  // Find the index in SwiftErrorVals.
-  SwiftErrorValues::iterator I = find(SwiftErrorVals, Val);
-  assert(I != SwiftErrorVals.end() && "Can't find value in SwiftErrorVals");
-  SwiftErrorMap[MBB][I - SwiftErrorVals.begin()] = VReg;
+void FunctionLoweringInfo::setCurrentSwiftErrorVReg(
+    const MachineBasicBlock *MBB, const Value *Val, unsigned VReg) {
+  SwiftErrorVRegDefMap[std::make_pair(MBB, Val)] = VReg;
 }