[llvm] r216640 - [FastISel] Undo phi node updates when falling-back to SelectionDAG.

[Juergen Ributzka]

Author: ributzka
Date: Wed Aug 27 21:06:55 2014
New Revision: 216640

URL: http://llvm.org/viewvc/llvm-project?rev=216640&view=rev
Log:
[FastISel] Undo phi node updates when falling-back to SelectionDAG.

The included test case would fail, because the MI PHI node would have two
operands from the same predecessor.

This problem occurs when a switch instruction couldn't be selected. This happens
always, because there is no default switch support for FastISel to begin with.

The problem was that FastISel would first add the operand to the PHI nodes and
then fall-back to SelectionDAG, which would then in turn add the same operands
to the PHI nodes again.

This fix removes these duplicate PHI node operands by reseting the
PHINodesToUpdate to its original state before FastISel tried to select the
instruction.

This fixes <rdar://problem/18155224>.

Added:
    llvm/trunk/test/CodeGen/AArch64/fast-isel-switch-phi.ll
Modified:
    llvm/trunk/include/llvm/CodeGen/FunctionLoweringInfo.h
    llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp

Modified: llvm/trunk/include/llvm/CodeGen/FunctionLoweringInfo.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/FunctionLoweringInfo.h?rev=216640&r1=216639&r2=216640&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/FunctionLoweringInfo.h (original)
+++ llvm/trunk/include/llvm/CodeGen/FunctionLoweringInfo.h Wed Aug 27 21:06:55 2014
@@ -115,6 +115,7 @@ public:
   /// TODO: This isn't per-function state, it's per-basic-block state. But
   /// there's no other convenient place for it to live right now.
   std::vector<std::pair<MachineInstr*, unsigned> > PHINodesToUpdate;
+  unsigned OrigNumPHINodesToUpdate;
 
   /// If the current MBB is a landing pad, the exception pointer and exception
   /// selector registers are copied into these virtual registers by

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp?rev=216640&r1=216639&r2=216640&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/FastISel.cpp Wed Aug 27 21:06:55 2014
@@ -1370,6 +1370,9 @@ FastISel::SelectInstruction(const Instru
     removeDeadCode(FuncInfo.InsertPt, SavedInsertPt);
 
   DbgLoc = DebugLoc();
+  // Undo phi node updates, because they will be added again by SelectionDAG.
+  if (isa<TerminatorInst>(I))
+    FuncInfo.PHINodesToUpdate.resize(FuncInfo.OrigNumPHINodesToUpdate);
   return false;
 }
 
@@ -2004,7 +2007,7 @@ bool FastISel::HandlePHINodesInSuccessor
   const TerminatorInst *TI = LLVMBB->getTerminator();
 
   SmallPtrSet<MachineBasicBlock *, 4> SuccsHandled;
-  unsigned OrigNumPHINodesToUpdate = FuncInfo.PHINodesToUpdate.size();
+  FuncInfo.OrigNumPHINodesToUpdate = FuncInfo.PHINodesToUpdate.size();
 
   // Check successor nodes' PHI nodes that expect a constant to be available
   // from this block.
@@ -2040,7 +2043,7 @@ bool FastISel::HandlePHINodesInSuccessor
         if (VT == MVT::i1 || VT == MVT::i8 || VT == MVT::i16)
           VT = TLI.getTypeToTransformTo(LLVMBB->getContext(), VT);
         else {
-          FuncInfo.PHINodesToUpdate.resize(OrigNumPHINodesToUpdate);
+          FuncInfo.PHINodesToUpdate.resize(FuncInfo.OrigNumPHINodesToUpdate);
           return false;
         }
       }
@@ -2054,8 +2057,8 @@ bool FastISel::HandlePHINodesInSuccessor
         DbgLoc = Inst->getDebugLoc();
 
       unsigned Reg = getRegForValue(PHIOp);
-      if (Reg == 0) {
-        FuncInfo.PHINodesToUpdate.resize(OrigNumPHINodesToUpdate);
+      if (!Reg) {
+        FuncInfo.PHINodesToUpdate.resize(FuncInfo.OrigNumPHINodesToUpdate);
         return false;
       }
       FuncInfo.PHINodesToUpdate.push_back(std::make_pair(MBBI++, Reg));

Added: llvm/trunk/test/CodeGen/AArch64/fast-isel-switch-phi.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/fast-isel-switch-phi.ll?rev=216640&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/AArch64/fast-isel-switch-phi.ll (added)
+++ llvm/trunk/test/CodeGen/AArch64/fast-isel-switch-phi.ll Wed Aug 27 21:06:55 2014
@@ -0,0 +1,26 @@
+; RUN: llc -mtriple=aarch64-apple-darwin -fast-isel -verify-machineinstrs < %s
+; REQUIRES: asserts
+
+; Test that the Machine Instruction PHI node doesn't have more than one operand
+; from the same predecessor.
+define i32 @foo(i32 %a, i32 %b, i1 %c) {
+entry:
+  br i1 %c, label %switch, label %direct
+
+switch:
+  switch i32 %a, label %exit [
+    i32 43, label %continue
+    i32 45, label %continue
+  ]
+
+direct:
+  %var = add i32 %b, 1
+  br label %continue
+
+continue:
+  %var.phi = phi i32 [ %var, %direct ], [ 0, %switch ], [ 0, %switch ]
+  ret i32 %var.phi
+
+exit:
+  ret i32 1
+}