Bug 1279312 - Use WasmTlsReg in baseline Wasm compiler. r=lth

Allocate an additional slot in localInfo_ and use it to save the incoming TLS
pointer. When setting up arguments for a function call, get the TLS pointer from
that local slot. Also preserve the TLS pointer register by reloading it before
returning.

This makes the Baseline ABI compatible with the Ion ABI.

js/src/asmjs/WasmBaselineCompile.cpp

@@ -472,6 +472,10 @@ class BaseCompiler
     Vector<Local, 8, SystemAllocPolicy> localInfo_;
     Vector<OutOfLineCode*, 8, SystemAllocPolicy> outOfLine_;
 
+    // Index into localInfo_ of the special local used for saving the TLS
+    // pointer. This follows the function's real arguments and locals.
+    uint32_t                    tlsSlot_;
+
     // On specific platforms we sometimes need to use specific registers.
 
 #ifdef JS_CODEGEN_X64
@@ -574,6 +578,10 @@ class BaseCompiler
 #endif
     }
 
+    void storeToFramePtr(Register r, int32_t offset) {
+        masm.storePtr(r, Address(StackPointer, localOffsetToSPOffset(offset)));
+    }
+
     void storeToFrameF64(FloatRegister r, int32_t offset) {
         masm.storeDouble(r, Address(StackPointer, localOffsetToSPOffset(offset)));
     }
@@ -594,6 +602,10 @@ class BaseCompiler
 #endif
     }
 
+    void loadFromFramePtr(Register r, int32_t offset) {
+        masm.loadPtr(Address(StackPointer, localOffsetToSPOffset(offset)), r);
+    }
+
     void loadFromFrameF64(FloatRegister r, int32_t offset) {
         masm.loadDouble(Address(StackPointer, localOffsetToSPOffset(offset)), r);
     }
@@ -1783,6 +1795,10 @@ class BaseCompiler
             }
         }
 
+        // The TLS pointer is always passed as a hidden argument in WasmTlsReg.
+        // Save it into its assigned local slot.
+        storeToFramePtr(WasmTlsReg, localInfo_[tlsSlot_].offs());
+
         // Initialize the stack locals to zero.
         //
         // TODO / OPTIMIZE: on x64, at least, scratch will be a 64-bit
@@ -1817,7 +1833,7 @@ class BaseCompiler
         masm.movePtr(masm.getStackPointer(), ABINonArgReg0);
         masm.subPtr(Imm32(maxFramePushed_ - localSize_), ABINonArgReg0);
         masm.branchPtr(Assembler::Below,
-                       SymbolicAddress::StackLimit,
+                       Address(WasmTlsReg, offsetof(wasm::TlsData, stackLimit)),
                        ABINonArgReg0,
                        &bodyLabel_);
 
@@ -1831,6 +1847,10 @@ class BaseCompiler
 
         masm.bind(&returnLabel_);
 
+        // The return value was set up before jumping here, but we also need to
+        // preserve the TLS register.
+        loadFromFramePtr(WasmTlsReg, frameOffsetFromSlot(tlsSlot_, MIRType::Pointer));
+
         wasm::GenerateFunctionEpilogue(masm, localSize_, &compileResults_.offsets());
 
 #if defined(JS_ION_PERF)
@@ -4995,6 +5015,11 @@ BaseCompiler::emitCallArgs(const ValTypeVector& args, FunctionCall& baselineCall
         passArg(baselineCall, argType, arg);
     }
 
+    // Always pass the TLS pointer as a hidden argument in WasmTlsReg.
+    // Load it directly out if its stack slot so we don't interfere with the
+    // stk_.
+    loadFromFramePtr(WasmTlsReg, frameOffsetFromSlot(tlsSlot_, MIRType::Pointer));
+
     if (!iter_.readCallArgsEnd(numArgs))
         return false;
 
@@ -6552,6 +6577,7 @@ BaseCompiler::BaseCompiler(const ModuleGeneratorData& mg,
 #ifdef DEBUG
       scratchRegisterTaken_(false),
 #endif
+      tlsSlot_(0),
 #ifdef JS_CODEGEN_X64
       specific_rax(RegI64(Register64(rax))),
       specific_rcx(RegI64(Register64(rcx))),
@@ -6615,7 +6641,11 @@ BaseCompiler::init()
 
     const ValTypeVector& args = func_.sig().args();
 
-    if (!localInfo_.resize(locals_.length()))
+    // localInfo_ contains an entry for every local in locals_, followed by
+    // entries for special locals. Currently the only special local is the TLS
+    // pointer.
+    tlsSlot_ = locals_.length();
+    if (!localInfo_.resize(locals_.length() + 1))
         return false;
 
     localSize_ = 0;
@@ -6652,6 +6682,10 @@ BaseCompiler::init()
         }
     }
 
+    // Reserve a stack slot for the TLS pointer before the varLow - varHigh
+    // range so it isn't zero-filled like the normal locals.
+    localInfo_[tlsSlot_].init(MIRType::Pointer, pushLocal(sizeof(void*)));
+
     varLow_ = localSize_;
 
     for (size_t i = args.length(); i < locals_.length(); i++) {