WebAssembly: don't optimize frameindex store

The previous code was incorrect (can't getReg a frameindex). We could instead optimize it to reduce tree height, but I'm not sure that's worthwhile yet because we then try to eliminate the frameindex.

This patch also fixes frame index elimination for operations which may load or store: it used to assume the base was operand 2 and immediate offset operand 1. That's not true for stores, where they're 4 and 3.

llvm-svn: 259305

llvm/lib/Target/WebAssembly/WebAssemblyRegisterInfo.cpp

@@ -74,8 +74,9 @@ void WebAssemblyRegisterInfo::eliminateFrameIndex(
       // generate broken code.
       report_fatal_error("Memory offset field overflow");
     }
-    MI.getOperand(1).setImm(Offset);
-    MI.getOperand(2).ChangeToRegister(WebAssembly::SP32, /*IsDef=*/false);
+    MI.getOperand(FIOperandNum - 1).setImm(Offset);
+    MI.getOperand(FIOperandNum)
+        .ChangeToRegister(WebAssembly::SP32, /*IsDef=*/false);
   } else {
     // Otherwise create an i32.add SP, offset and make it the operand.
     auto &MRI = MF.getRegInfo();

llvm/lib/Target/WebAssembly/WebAssemblyStoreResults.cpp

@@ -134,10 +134,17 @@ bool WebAssemblyStoreResults::runOnMachineFunction(MachineFunction &MF) {
       case WebAssembly::STORE_F64:
       case WebAssembly::STORE_I32:
       case WebAssembly::STORE_I64: {
-        unsigned ToReg = MI.getOperand(0).getReg();
-        unsigned FromReg =
-            MI.getOperand(WebAssembly::StoreValueOperandNo).getReg();
-        Changed |= ReplaceDominatedUses(MBB, MI, FromReg, ToReg, MRI, MDT);
+        const auto &Stored = MI.getOperand(WebAssembly::StoreValueOperandNo);
+        if (Stored.isReg()) {
+          unsigned ToReg = MI.getOperand(0).getReg();
+          unsigned FromReg = Stored.getReg();
+          Changed |= ReplaceDominatedUses(MBB, MI, FromReg, ToReg, MRI, MDT);
+        } else if (Stored.isFI()) {
+          break;
+        } else {
+          report_fatal_error(
+              "Store results: store not consuming reg or frame index");
+        }
         break;
       }
       case WebAssembly::CALL_I32:

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

@@ -59,3 +59,13 @@ for.body5.i:
 for.cond.cleanup4.i:
   ret void
 }
+
+; CHECK-LABEL: fi_ret:
+; CHECK: i32.store $discard=,
+define hidden i8* @fi_ret(i8** %addr) {
+entry:
+  %buf = alloca [27 x i8], align 16
+  %0 = getelementptr inbounds [27 x i8], [27 x i8]* %buf, i32 0, i32 0
+  store i8* %0, i8** %addr
+  ret i8* %0
+}