[WebAssembly] Add a test for wasm-store-results pass

[dschuff]

Currently there are no tests at all so one test is better than none :), I'm open to suggestions for more.

[sunfish]

Please add a little one-line comment at the top of the file describing what's being tested.

Otherwise, lgtm. Thanks for catching this.

test/CodeGen/WebAssembly/store-results.ll

13 ↗

(On Diff #41690)

The volatile here isn't necessary.

[dschuff]

• Add comment

llvm/trunk/lib/Target/WebAssembly/WebAssemblyStoreResults.cpp

bool WebAssemblyStoreResults::runOnMachineFunction(MachineFunction &MF) {
   DEBUG({
     dbgs() << "********** Store Results **********\n"
            << "********** Function: " << MF.getName() << '\n';
   });
 
   const MachineRegisterInfo &MRI = MF.getRegInfo();
   MachineDominatorTree &MDT = getAnalysis<MachineDominatorTree>();
 
-  for (auto &MBB : MF)
+  for (auto &MBB : MF) {
+    DEBUG(dbgs() << "Basic Block: " << MBB.getName() << '\n');
     for (auto &MI : MBB)
       switch (MI.getOpcode()) {
       default:
         break;
       case WebAssembly::STORE8_I32:
       case WebAssembly::STORE16_I32:
       case WebAssembly::STORE8_I64:
       case WebAssembly::STORE16_I64:
       case WebAssembly::STORE32_I64:
       case WebAssembly::STORE_F32:
       case WebAssembly::STORE_F64:
       case WebAssembly::STORE_I32:
       case WebAssembly::STORE_I64:
         unsigned ToReg = MI.getOperand(0).getReg();
         unsigned FromReg = MI.getOperand(2).getReg();
         for (auto I = MRI.use_begin(FromReg), E = MRI.use_end(); I != E;) {
           MachineOperand &O = *I++;
           MachineInstr *Where = O.getParent();
           if (Where->getOpcode() == TargetOpcode::PHI)
             Where = Where->getOperand(&O - &Where->getOperand(0) + 1)
                         .getMBB()
                         ->getFirstTerminator();
           if (&MI == Where || !MDT.dominates(&MI, Where))
             continue;
+          DEBUG(dbgs() << "Setting operand " << O << " in " << *Where <<
+                " from " << MI <<"\n");
           O.setReg(ToReg);
         }
       }
+  }
 
   return true;
 }

llvm/trunk/test/CodeGen/WebAssembly/store-results.ll

+; RUN: llc < %s -asm-verbose=false | FileCheck %s
+
+; Test that the wasm-store-results pass makes users of stored values use the
+; result of store expressions to reduce get_local/set_local traffic.
+
+target datalayout = "e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+; CHECK-LABEL: single_block:
+; CHECK-NOT: .local
+; CHECK: i32.const $push{{[0-9]+}}=, 0
+; CHECK: i32.store $push[[STORE:[0-9]+]]=, $0, $pop{{[0-9]+}}
+; CHECK: return $pop[[STORE]]{{$}}
+define i32 @single_block(i32* %p) {
+entry:
+  store i32 0, i32* %p
+  ret i32 0
+}