[WebAssembly] Implement prolog/epilog insertion and FrameIndex elimination

Summary:
Use the SP32 physical register as the base for FrameIndex
lowering. Update it and the __stack_pointer global var in the prolog and
epilog. Extend the mapping of virtual registers to wasm locals to
include the physical registers.

Rather than modify the target-independent PrologEpilogInserter (which
asserts that there are no virtual registers left) include a
slightly-modified copy for Wasm that does not have this assertion and
only clears the virtual registers if scavenging was needed (which of
course it isn't for wasm).

Differential Revision: http://reviews.llvm.org/D15344

llvm-svn: 255392

1 files changed, 31 insertions, 4 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyRegisterInfo.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyRegisterInfo.cpp
index f87b547e3f5..dcada45f96d 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyRegisterInfo.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyRegisterInfo.cpp
@@ -52,10 +52,37 @@ WebAssemblyRegisterInfo::getReservedRegs(const MachineFunction & /*MF*/) const {
 }
 
 void WebAssemblyRegisterInfo::eliminateFrameIndex(
-    MachineBasicBlock::iterator /*II*/, int /*SPAdj*/,
-    unsigned /*FIOperandNum*/, RegScavenger * /*RS*/) const {
-  llvm_unreachable(
-      "TODO: implement WebAssemblyRegisterInfo::eliminateFrameIndex");
+    MachineBasicBlock::iterator II, int SPAdj,
+    unsigned FIOperandNum, RegScavenger * /*RS*/) const {
+  assert(SPAdj == 0);
+  MachineInstr &MI = *II;
+
+  MachineBasicBlock &MBB = *MI.getParent();
+  MachineFunction &MF = *MBB.getParent();
+  int FrameIndex = MI.getOperand(FIOperandNum).getIndex();
+  const MachineFrameInfo& MFI = *MF.getFrameInfo();
+  int FrameOffset = MFI.getStackSize() + MFI.getObjectOffset(FrameIndex);
+
+  if (MI.mayLoadOrStore()) {
+    // If this is a load or store, make it relative to SP and fold the frame
+    // offset directly in
+    assert(MI.getOperand(1).getImm() == 0 &&
+           "Can't eliminate FI yet if offset is already set");
+    MI.getOperand(1).setImm(FrameOffset);
+    MI.getOperand(2).ChangeToRegister(WebAssembly::SP32, /*IsDef=*/false);
+  } else {
+    // Otherwise create an i32.add SP, offset and make it the operand
+    auto &MRI = MF.getRegInfo();
+    const auto *TII = MF.getSubtarget().getInstrInfo();
+
+    unsigned OffsetReg = MRI.createVirtualRegister(&WebAssembly::I32RegClass);
+    BuildMI(MBB, MI, MI.getDebugLoc(), TII->get(WebAssembly::CONST_I32), OffsetReg)
+        .addImm(FrameOffset);
+    BuildMI(MBB, MI, MI.getDebugLoc(), TII->get(WebAssembly::ADD_I32), OffsetReg)
+        .addReg(WebAssembly::SP32)
+        .addReg(OffsetReg);
+    MI.getOperand(FIOperandNum).ChangeToRegister(OffsetReg, /*IsDef=*/false);
+  }
 }
 
 unsigned