[WebAssembly] FastISel: Don't fallback to SelectionDAG after BuildMI in selectCall

[sbc100]

Summary

My understanding is that once BuildMI has been called we can't fallback
to SelectionDAG.

This change moves the fallback for when getRegForValue() fails for
that target of an indirect call. This was failing in -fPIC mode when
the callee is GlobalValue.

[sbc100]

Looks like this was first introduced in rL319144, but none of our test cases currently hit the return.

I have so far failed to build fine a reasonable sized test case.

[sbc100]

bad-reduced.bc30 KBDownload

[sbc100]

Attached my reproducer which hits this return when run with llc -fast-isel -filetype=obj -relocation-model=pic bad-reduced.bc

[sbc100]

• add test

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

else
       Reg = getRegForValue(V);
 
     if (Reg == 0)
       return false;
 
     Args.push_back(Reg);
   }
 
+  unsigned CalleeReg = 0;
+  if (!IsDirect) {
+    CalleeReg = getRegForValue(Call->getCalledValue());
+    if (!CalleeReg)
+      return false;
+  }
+
   auto MIB = BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc, TII.get(Opc));
 
   if (!IsVoid)
     MIB.addReg(ResultReg, RegState::Define);
 
   if (IsDirect)
     MIB.addGlobalAddress(Func);
-  else {
-    unsigned Reg = getRegForValue(Call->getCalledValue());
-    if (Reg == 0)
-      return false;
-    MIB.addReg(Reg);
-  }
+  else
+    MIB.addReg(CalleeReg);
 
   for (unsigned ArgReg : Args)
     MIB.addReg(ArgReg);
 
   if (!IsVoid)
     updateValueMap(Call, ResultReg);
   return true;
 }

llvm/trunk/test/CodeGen/WebAssembly/call-pic.ll

 ; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers -relocation-model=pic -fast-isel=1 | FileCheck %s
 ; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers -relocation-model=pic -fast-isel=0 | FileCheck %s
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
 
 declare i32 @foo()
 declare i32 @bar()
 declare hidden i32 @hidden_function()
 
 @indirect_func = global i32 ()* @foo
+@alias_func = hidden alias i32 (), i32 ()* @local_function
+
+define i32 @local_function() {
+  ret i32 1
+}
 
 define void @call_indirect_func() {
 ; CHECK-LABEL: call_indirect_func:
 ; CHECK:      global.get $push[[L0:[0-9]+]]=, __memory_base{{$}}
 ; CHECK-NEXT: i32.const $push[[L1:[0-9]+]]=, indirect_func@MBREL{{$}}
 ; CHECK-NEXT: i32.add $push[[L2:[0-9]+]]=, $pop[[L0]], $pop[[L1]]{{$}}
 ; CHECK-NEXT: i32.load $push[[L3:[0-9]+]]=, 0($pop[[L2]]){{$}}
 ; CHECK-NEXT: i32.call_indirect $push[[L4:[0-9]+]]=, $pop[[L3]]{{$}}
   %1 = load i32 ()*, i32 ()** @indirect_func, align 4
   %call = call i32 %1()
   ret void
 }
 
 define void @call_direct() {
 ; CHECK-LABEL: call_direct:
 ; CHECK: .functype call_direct () -> ()
 ; CHECK-NEXT: i32.call $push0=, foo{{$}}
 ; CHECK-NEXT: drop $pop0{{$}}
 ; CHECK-NEXT: return{{$}}
   %call = call i32 @foo()
   ret void
 }
 
+define void @call_alias_func() {
+; CHECK-LABEL: call_alias_func:
+; CHECK: .functype call_alias_func () -> ()
+; CHECK-NEXT: i32.call $push0=, alias_func
+; CHECK-NEXT: drop $pop0{{$}}
+; CHECK-NEXT: return{{$}}
+  %call = call i32 @alias_func()
+  ret void
+}
+
 define i8* @get_function_address() {
 ; CHECK-LABEL: get_function_address:
 ; CHECK:       global.get $push[[L0:[0-9]+]]=, bar@GOT{{$}}
 ; CHECK-NEXT:  return $pop[[L0]]{{$}}
 ; CHECK-NEXT:  end_function{{$}}
 
   ret i8* bitcast (i32 ()* @bar to i8*)
 }