Pull in r339734 from upstream llvm trunk (by Eli Friedman):

  [ARM] Make PerformSHLSimplify add nodes to the DAG worklist correctly.

  Intentionally excluding nodes from the DAGCombine worklist is likely
  to lead to weird optimizations and infinite loops, so it's generally
  a bad idea.

  To avoid the infinite loops, fix DAGCombine to use the
  isDesirableToCommuteWithShift target hook before performing the
  transforms in question, and implement the target hook in the ARM
  backend disable the transforms in question.

  Fixes https://bugs.llvm.org/show_bug.cgi?id=38530 . (I don't have a
  reduced testcase for that bug. But we should have sufficient test
  coverage for PerformSHLSimplify given that we're not playing weird
  tricks with the worklist. I can try to bugpoint it if necessary,
  though.)

  Differential Revision: https://reviews.llvm.org/D50667

This should fix a possible hang when compiling sys/dev/nxge/if_nxge.c
(which exists now only in the stable/11 branch) for arm.

4 files changed, 28 insertions, 5 deletions

diff --git a/contrib/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/contrib/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index cfc7aa96d31f..75b8036779ba 100644
--- a/contrib/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/contrib/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -8496,7 +8496,9 @@ AArch64TargetLowering::getScratchRegisters(CallingConv::ID) const {
 }
 
 bool
-AArch64TargetLowering::isDesirableToCommuteWithShift(const SDNode *N) const {
+AArch64TargetLowering::isDesirableToCommuteWithShift(const SDNode *N,
+                                                     CombineLevel Level) const {
+  N = N->getOperand(0).getNode();
   EVT VT = N->getValueType(0);
     // If N is unsigned bit extraction: ((x >> C) & mask), then do not combine
     // it with shift to let it be lowered to UBFX.
diff --git a/contrib/llvm/lib/Target/AArch64/AArch64ISelLowering.h b/contrib/llvm/lib/Target/AArch64/AArch64ISelLowering.h
index d783c8a6048c..a6d66aeae043 100644
--- a/contrib/llvm/lib/Target/AArch64/AArch64ISelLowering.h
+++ b/contrib/llvm/lib/Target/AArch64/AArch64ISelLowering.h
@@ -363,7 +363,8 @@ public:
   const MCPhysReg *getScratchRegisters(CallingConv::ID CC) const override;
 
   /// Returns false if N is a bit extraction pattern of (X >> C) & Mask.
-  bool isDesirableToCommuteWithShift(const SDNode *N) const override;
+  bool isDesirableToCommuteWithShift(const SDNode *N,
+                                     CombineLevel Level) const override;
 
   /// Returns true if it is beneficial to convert a load of a constant
   /// to just the constant itself.
diff --git a/contrib/llvm/lib/Target/ARM/ARMISelLowering.cpp b/contrib/llvm/lib/Target/ARM/ARMISelLowering.cpp
index ede276dd91bb..a763e29b9f60 100644
--- a/contrib/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/contrib/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -10407,6 +10407,25 @@ static SDValue PerformADDCombineWithOperands(SDNode *N, SDValue N0, SDValue N1,
   return SDValue();
 }
 
+bool
+ARMTargetLowering::isDesirableToCommuteWithShift(const SDNode *N,
+                                                 CombineLevel Level) const {
+  if (Level == BeforeLegalizeTypes)
+    return true;
+
+  if (Subtarget->isThumb() && Subtarget->isThumb1Only())
+    return true;
+
+  if (N->getOpcode() != ISD::SHL)
+    return true;
+
+  // Turn off commute-with-shift transform after legalization, so it doesn't
+  // conflict with PerformSHLSimplify.  (We could try to detect when
+  // PerformSHLSimplify would trigger more precisely, but it isn't
+  // really necessary.)
+  return false;
+}
+
 static SDValue PerformSHLSimplify(SDNode *N,
                                 TargetLowering::DAGCombinerInfo &DCI,
                                 const ARMSubtarget *ST) {
@@ -10506,9 +10525,7 @@ static SDValue PerformSHLSimplify(SDNode *N,
   LLVM_DEBUG(dbgs() << "Simplify shl use:\n"; SHL.getOperand(0).dump();
              SHL.dump(); N->dump());
   LLVM_DEBUG(dbgs() << "Into:\n"; X.dump(); BinOp.dump(); Res.dump());
-
-  DAG.ReplaceAllUsesWith(SDValue(N, 0), Res);
-  return SDValue(N, 0);
+  return Res;
 }
 
 
diff --git a/contrib/llvm/lib/Target/ARM/ARMISelLowering.h b/contrib/llvm/lib/Target/ARM/ARMISelLowering.h
index 50b4c2977fb5..7e7016d1639c 100644
--- a/contrib/llvm/lib/Target/ARM/ARMISelLowering.h
+++ b/contrib/llvm/lib/Target/ARM/ARMISelLowering.h
@@ -583,6 +583,9 @@ class VectorType;
     unsigned getABIAlignmentForCallingConv(Type *ArgTy,
                                            DataLayout DL) const override;
 
+    bool isDesirableToCommuteWithShift(const SDNode *N,
+                                       CombineLevel Level) const override;
+
   protected:
     std::pair<const TargetRegisterClass *, uint8_t>
     findRepresentativeClass(const TargetRegisterInfo *TRI,