[WebAssembly] Initial implementation of PIC code generation

This change implements lowering of references global symbols in PIC
mode.

This change implements lowering of global references in PIC mode using a
new @GOT reference type. @GOT references can be used with function or
data symbol names combined with the get_global instruction. In this case
the linker will insert the wasm global that stores the address of the
symbol (either in memory for data symbols or in the wasm table for
function symbols).

For now I'm continuing to use the R_WASM_GLOBAL_INDEX_LEB relocation
type for this type of reference which means that this relocation type
can refer to either a global or a function or data symbol. We could
choose to introduce specific relocation types for GOT entries in the
future.  See the current dynamic linking proposal:

https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md

Differential Revision: https://reviews.llvm.org/D54647

llvm-svn: 357022

1 files changed, 13 insertions, 5 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
index 15df3d4..1705748 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
@@ -151,7 +151,7 @@ private:
     return MVT::INVALID_SIMPLE_VALUE_TYPE;
   }
   bool computeAddress(const Value *Obj, Address &Addr);
-  void materializeLoadStoreOperands(Address &Addr);
+  bool materializeLoadStoreOperands(Address &Addr);
   void addLoadStoreOperands(const Address &Addr, const MachineInstrBuilder &MIB,
                             MachineMemOperand *MMO);
   unsigned maskI1Value(unsigned Reg, const Value *V);
@@ -374,10 +374,13 @@ bool WebAssemblyFastISel::computeAddress(const Value *Obj, Address &Addr) {
   return Addr.getReg() != 0;
 }
 
-void WebAssemblyFastISel::materializeLoadStoreOperands(Address &Addr) {
+bool WebAssemblyFastISel::materializeLoadStoreOperands(Address &Addr) {
   if (Addr.isRegBase()) {
     unsigned Reg = Addr.getReg();
     if (Reg == 0) {
+      const GlobalValue *GV = Addr.getGlobalValue();
+      if (GV && TLI.isPositionIndependent())
+        return false;
       Reg = createResultReg(Subtarget->hasAddr64() ? &WebAssembly::I64RegClass
                                                    : &WebAssembly::I32RegClass);
       unsigned Opc = Subtarget->hasAddr64() ? WebAssembly::CONST_I64
@@ -387,6 +390,7 @@ void WebAssemblyFastISel::materializeLoadStoreOperands(Address &Addr) {
       Addr.setReg(Reg);
     }
   }
+  return true;
 }
 
 void WebAssemblyFastISel::addLoadStoreOperands(const Address &Addr,
@@ -604,7 +608,9 @@ unsigned WebAssemblyFastISel::fastMaterializeAlloca(const AllocaInst *AI) {
 }
 
 unsigned WebAssemblyFastISel::fastMaterializeConstant(const Constant *C) {
-  if (const auto *GV = dyn_cast<GlobalValue>(C)) {
+  if (const GlobalValue *GV = dyn_cast<GlobalValue>(C)) {
+    if (TLI.isPositionIndependent())
+      return 0;
     unsigned ResultReg =
         createResultReg(Subtarget->hasAddr64() ? &WebAssembly::I64RegClass
                                                : &WebAssembly::I32RegClass);
@@ -1181,7 +1187,8 @@ bool WebAssemblyFastISel::selectLoad(const Instruction *I) {
     return false;
   }
 
-  materializeLoadStoreOperands(Addr);
+  if (!materializeLoadStoreOperands(Addr))
+    return false;
 
   unsigned ResultReg = createResultReg(RC);
   auto MIB = BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(Opc),
@@ -1233,7 +1240,8 @@ bool WebAssemblyFastISel::selectStore(const Instruction *I) {
     return false;
   }
 
-  materializeLoadStoreOperands(Addr);
+  if (!materializeLoadStoreOperands(Addr))
+    return false;
 
   unsigned ValueReg = getRegForValue(Store->getValueOperand());
   if (ValueReg == 0)