Revert "Add peephole optimisation"

This reverts commit c8ad813.

Author: majaha

llvm/lib/Target/WebAssembly/WebAssemblyDebugFixup.cpp

@@ -122,20 +122,9 @@ bool WebAssemblyDebugFixup::runOnMachineFunction(MachineFunction &MF) {
           // it will be culled later.
         }
       } else {
-        
-        // WebAssembly Peephole optimisation can remove instructions around wasm unreachable.
-        // This is valid for wasm, as unreachable is operand stack polymorphic. But this is not modeled
-        // in llvm at the moment, and so the stack may not seem to pop all that it pushes.
-        // Clear the stack so we don't violate the assert(Stack.empty()) later on.
-        if (MI.getOpcode() == WebAssembly::UNREACHABLE) {
-          Stack.clear();
-          break;
-        }
-
         // Track stack depth.
         for (MachineOperand &MO : reverse(MI.explicit_uses())) {
           if (MO.isReg() && MFI.isVRegStackified(MO.getReg())) {
-            assert(Stack.size() != 0 && "WebAssemblyDebugFixup: Pop: Operand stack empty!");
             auto Prev = Stack.back();
             Stack.pop_back();
             assert(Prev.Reg == MO.getReg() &&

llvm/lib/Target/WebAssembly/WebAssemblyPeephole.cpp

@@ -20,7 +20,6 @@
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
-#include <iterator>
 using namespace llvm;
 
 #define DEBUG_TYPE "wasm-peephole"
@@ -110,53 +109,6 @@ static bool maybeRewriteToFallthrough(MachineInstr &MI, MachineBasicBlock &MBB,
   return true;
 }
 
-static bool eraseDeadCodeAroundUnreachable(MachineInstr &UnreachbleMI, MachineBasicBlock &MBB) {
-  SmallVector<MachineInstr*, 16> ToDelete;
-
-  // Because wasm unreachable is stack polymorphic and unconditionally ends control,
-  // all instructions after it can be removed until the end of this block.
-  // We remove the common case of double unreachable.
-  auto ForwardsIterator = UnreachbleMI.getIterator();
-  for (ForwardsIterator++; !ForwardsIterator.isEnd(); ForwardsIterator++) {
-    MachineInstr& MI = *ForwardsIterator;
-    if (MI.getOpcode() == WebAssembly::UNREACHABLE) {
-      ToDelete.push_back(&MI);
-    } else {
-      break;
-    }
-  }
-
-  [&]() {
-    // For the same reasons as above, previous instructions that only affect
-    // local function state can be removed (e.g. local.set, drop, various reads).
-    // We remove the common case of "drop unreachable".
-    auto BackwardsIterator = UnreachbleMI.getReverseIterator();
-    for (BackwardsIterator++; !BackwardsIterator.isEnd(); BackwardsIterator++) {
-      MachineInstr& MI = *BackwardsIterator;
-      switch(MI.getOpcode()) {
-      case WebAssembly::DROP_I32:
-      case WebAssembly::DROP_I64:
-      case WebAssembly::DROP_F32:
-      case WebAssembly::DROP_F64:
-      case WebAssembly::DROP_EXTERNREF:
-      case WebAssembly::DROP_FUNCREF:
-      case WebAssembly::DROP_V128:
-        ToDelete.push_back(&MI);
-        continue;
-      default:
-        return;
-      }
-    }
-  }();
-
-  bool Changed = false;
-  for (MachineInstr* MI : ToDelete) {
-    MI->eraseFromParent();
-    Changed = true;
-  }
-  return Changed;
-}
-
 bool WebAssemblyPeephole::runOnMachineFunction(MachineFunction &MF) {
   LLVM_DEBUG({
     dbgs() << "********** Peephole **********\n"
@@ -207,9 +159,6 @@ bool WebAssemblyPeephole::runOnMachineFunction(MachineFunction &MF) {
       case WebAssembly::RETURN:
         Changed |= maybeRewriteToFallthrough(MI, MBB, MF, MFI, MRI, TII);
         break;
-      case WebAssembly::UNREACHABLE:
-        Changed |= eraseDeadCodeAroundUnreachable(MI, MBB);
-        break;
       }
 
   return Changed;

llvm/test/CodeGen/WebAssembly/unreachable.ll

@@ -41,6 +41,7 @@ define void @trap_unreach() {
 ; CHECK:         .functype trap_unreach () -> ()
 ; CHECK-NEXT:  # %bb.0:
 ; CHECK-NEXT:    unreachable
+; CHECK-NEXT:    unreachable
 ; CHECK-NEXT:    end_function
   call void @llvm.trap()
   unreachable
@@ -98,6 +99,7 @@ define i32 @i32_sig_match_unreach() {
 ; CHECK:         .functype i32_sig_match_unreach () -> (i32)
 ; CHECK-NEXT:  # %bb.0:
 ; CHECK-NEXT:    call ext_func_i32
+; CHECK-NEXT:    drop
 ; CHECK-NEXT:    unreachable
 ; CHECK-NEXT:    end_function
   call i32 @ext_func_i32()

llvm/test/MC/WebAssembly/global-ctor-dtor.ll

@@ -80,29 +80,29 @@ declare void @func3()
 ; CHECK-NEXT:         Offset:          0x1D
 ; CHECK-NEXT:       - Type:            R_WASM_FUNCTION_INDEX_LEB
 ; CHECK-NEXT:         Index:           6
-; CHECK-NEXT:         Offset:          0x2B
+; CHECK-NEXT:         Offset:          0x2C
 ; CHECK-NEXT:       - Type:            R_WASM_TABLE_INDEX_SLEB
 ; CHECK-NEXT:         Index:           5
-; CHECK-NEXT:         Offset:          0x36
+; CHECK-NEXT:         Offset:          0x37
 ; CHECK-NEXT:       - Type:            R_WASM_MEMORY_ADDR_SLEB
 ; CHECK-NEXT:         Index:           3
-; CHECK-NEXT:         Offset:          0x3E
+; CHECK-NEXT:         Offset:          0x3F
 ; CHECK-NEXT:       - Type:            R_WASM_FUNCTION_INDEX_LEB
 ; CHECK-NEXT:         Index:           4
-; CHECK-NEXT:         Offset:          0x44
+; CHECK-NEXT:         Offset:          0x45
 ; CHECK-NEXT:     Functions:
 ; CHECK-NEXT:       - Index:           5
 ; CHECK-NEXT:         Locals:
 ; CHECK-NEXT:         Body:            1080808080000B
 ; CHECK-NEXT:       - Index:           6
 ; CHECK-NEXT:         Locals:
-; CHECK-NEXT:         Body:            02404181808080004100418080808000108180808000450D00000B0B
+; CHECK-NEXT:         Body:            02404181808080004100418080808000108180808000450D0000000B0B
 ; CHECK-NEXT:       - Index:           7
 ; CHECK-NEXT:         Locals:
 ; CHECK-NEXT:         Body:            1082808080000B
 ; CHECK-NEXT:       - Index:           8
 ; CHECK-NEXT:         Locals:
-; CHECK-NEXT:         Body:            02404182808080004100418080808000108180808000450D00000B0B
+; CHECK-NEXT:         Body:            02404182808080004100418080808000108180808000450D0000000B0B
 ; CHECK-NEXT:   - Type:            DATA
 ; CHECK-NEXT:     Segments:
 ; CHECK-NEXT:       - SectionOffset:   6