[llvm] r304043 - [bpf] disallow global_addr+off folding

[Alexei Starovoitov via llvm-commits]

Author: ast
Date: Fri May 26 17:32:41 2017
New Revision: 304043

URL: http://llvm.org/viewvc/llvm-project?rev=304043&view=rev
Log:
[bpf] disallow global_addr+off folding

Wrong assembly code is generated for a simple program with
clang. If clang only produces IR and llc is used
for IR lowering and optimization, correct assembly
code is generated.

The main reason is that clang feeds default Reloc::Static
to llvm and llc feeds no RelocMode to llvm, where
for llc case, BPF backend picks up Reloc::PIC_ mode.
This leads different IR lowering behavior and clang
permits global_addr+off folding while llc doesn't.

This patch introduces isOffsetFoldingLegal function into
BPF backend and the function always return false.
This will make clang and llc behave the same for
the lowering.

Bug https://bugs.llvm.org//show_bug.cgi?id=33183
has more detailed explanation.

Signed-off-by: Yonghong Song <yhs at fb.com>
Signed-off-by: Alexei Starovoitov <ast at kernel.org>

Modified:
    llvm/trunk/lib/Target/BPF/BPFISelLowering.cpp
    llvm/trunk/lib/Target/BPF/BPFISelLowering.h

Modified: llvm/trunk/lib/Target/BPF/BPFISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/BPF/BPFISelLowering.cpp?rev=304043&r1=304042&r2=304043&view=diff
==============================================================================
--- llvm/trunk/lib/Target/BPF/BPFISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/BPF/BPFISelLowering.cpp Fri May 26 17:32:41 2017
@@ -132,6 +132,10 @@ BPFTargetLowering::BPFTargetLowering(con
   MaxStoresPerMemmove = MaxStoresPerMemmoveOptSize = 128;
 }
 
+bool BPFTargetLowering::isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const {
+  return false;
+}
+
 SDValue BPFTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   switch (Op.getOpcode()) {
   case ISD::BR_CC:
@@ -496,8 +500,11 @@ const char *BPFTargetLowering::getTarget
 
 SDValue BPFTargetLowering::LowerGlobalAddress(SDValue Op,
                                               SelectionDAG &DAG) const {
+  auto N = cast<GlobalAddressSDNode>(Op);
+  assert(N->getOffset() == 0 && "Invalid offset for global address");
+
   SDLoc DL(Op);
-  const GlobalValue *GV = cast<GlobalAddressSDNode>(Op)->getGlobal();
+  const GlobalValue *GV = N->getGlobal();
   SDValue GA = DAG.getTargetGlobalAddress(GV, DL, MVT::i64);
 
   return DAG.getNode(BPFISD::Wrapper, DL, MVT::i64, GA);

Modified: llvm/trunk/lib/Target/BPF/BPFISelLowering.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/BPF/BPFISelLowering.h?rev=304043&r1=304042&r2=304043&view=diff
==============================================================================
--- llvm/trunk/lib/Target/BPF/BPFISelLowering.h (original)
+++ llvm/trunk/lib/Target/BPF/BPFISelLowering.h Fri May 26 17:32:41 2017
@@ -42,6 +42,10 @@ public:
   // This method returns the name of a target specific DAG node.
   const char *getTargetNodeName(unsigned Opcode) const override;
 
+  // This method decides whether folding a constant offset
+  // with the given GlobalAddress is legal.
+  bool isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const override;
+
   MachineBasicBlock *
   EmitInstrWithCustomInserter(MachineInstr &MI,
                               MachineBasicBlock *BB) const override;