[WebAssembly] Make tied inline asm operands work again

Summary:
rL341389 broke code with tied register operands in inline assembly. For
example, `asm("" : "=r"(var) : "0"(var));`
The code above specifies the input operand to be in the same register
with the output operand, tying the two register. This patch makes this
kind of code work again.

Reviewers: dschuff

Subscribers: sbc100, jgravelle-google, eraman, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D51991

llvm-svn: 342084

lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp

@@ -316,6 +316,9 @@ bool WebAssemblyExplicitLocals::runOnMachineFunction(MachineFunction &MF) {
         if (MO.isDef()) {
           assert(MI.getOpcode() == TargetOpcode::INLINEASM);
           unsigned LocalId = getLocalId(Reg2Local, CurLocal, OldReg);
+          // If this register operand is tied to another operand, we can't
+          // change it to an immediate. Untie it first.
+          MI.untieRegOperand(MI.getOperandNo(&MO));
           MO.ChangeToImmediate(LocalId);
           continue;
         }
@@ -331,6 +334,8 @@ bool WebAssemblyExplicitLocals::runOnMachineFunction(MachineFunction &MF) {
         // indices as immediates.
         if (MI.getOpcode() == TargetOpcode::INLINEASM) {
           unsigned LocalId = getLocalId(Reg2Local, CurLocal, OldReg);
+          // Untie it first if this reg operand is tied to another operand.
+          MI.untieRegOperand(MI.getOperandNo(&MO));
           MO.ChangeToImmediate(LocalId);
           continue;
         }

test/CodeGen/WebAssembly/inline-asm.ll

@@ -97,6 +97,15 @@ entry:
   ret i32 %t0
 }
 
+; CHECK-LABEL: tied_operands
+; CHECK: get_local  $push0=, 0
+; CHECK: return    $pop0
+define i32 @tied_operands(i32 %var) {
+entry:
+  %ret = call i32 asm "", "=r,0"(i32 %var)
+  ret i32 %ret
+}
+
 attributes #0 = { nounwind }
 
 !0 = !{i32 47}