[WebAssembly] Fix selection of global calls

[aheejin]

Summary

When selecting calls, currently we unconditionally remove Wrappers of
the call target. But we are supposed to do that only when the target is
a function, an external symbol (= library function), or an alias of a
function. Otherwise we end up directly calling globals that are not
functions.

Fixes https://github.com/llvm/llvm-project/issues/60003.

[HerrCai0907]

LGTM

[tlively]

LGTM % comment clarification.

llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp

254

What is "it" at the beginning of this first sentence? Also, the second sentence has a lot of double (or triple?) negatives, so it slightly confusing.

[aheejin]

Improve comments

llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp

void WebAssemblyDAGToDAGISel::Select(SDNode *Node) {
   case WebAssemblyISD::RET_CALL: {
     // CALL has both variable operands and variable results, but ISel only
     // supports one or the other. Split calls into two nodes glued together, one
     // for the operands and one for the results. These two nodes will be
     // recombined in a custom inserter hook into a single MachineInstr.
     SmallVector<SDValue, 16> Ops;
     for (size_t i = 1; i < Node->getNumOperands(); ++i) {
       SDValue Op = Node->getOperand(i);
-      if (i == 1 && Op->getOpcode() == WebAssemblyISD::Wrapper)
-        Op = Op->getOperand(0);
+      // Remove the wrapper when the call target is a function, an external
+      // symbol (which will be lowered to a library function), or an alias of
+      // a function. If the target is not a function/external symbol, we
+      // shouldn't remove the wrapper, because we cannot call it directly and
+      // instead we want it to be loaded with a CONST instruction and called
+      // with a call_indirect later.
+      if (i == 1 && Op->getOpcode() == WebAssemblyISD::Wrapper) {
+        SDValue NewOp = Op->getOperand(0);
+        if (auto *GlobalOp = dyn_cast<GlobalAddressSDNode>(NewOp.getNode())) {
+          if (isa<Function>(
+                  GlobalOp->getGlobal()->stripPointerCastsAndAliases()))
+            Op = NewOp;
+        } else if (isa<ExternalSymbolSDNode>(NewOp.getNode())) {
+          Op = NewOp;
+        }
+      }
       Ops.push_back(Op);
     }
 
     // Add the chain last
     Ops.push_back(Node->getOperand(0));
     MachineSDNode *CallParams =
         CurDAG->getMachineNode(WebAssembly::CALL_PARAMS, DL, MVT::Glue, Ops);
 

llvm/test/CodeGen/WebAssembly/call.ll

-; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers -mattr=+sign-ext,+simd128 | FileCheck --check-prefixes=CHECK,NO-TAIL %s
-; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers -fast-isel -fast-isel-abort=1 -mattr=+sign-ext,+simd128 | FileCheck --check-prefixes=CHECK,NO-TAIL %s
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers -mattr=+sign-ext,+simd128 | FileCheck --check-prefixes=CHECK,SLOW,NO-TAIL %s
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers -fast-isel -fast-isel-abort=1 -mattr=+sign-ext,+simd128 | FileCheck --check-prefixes=CHECK,FAST,NO-TAIL %s
 ; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers -mattr=+sign-ext,+simd128,+tail-call | FileCheck --check-prefixes=CHECK,SLOW-TAIL %s
 ; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -wasm-keep-registers -fast-isel -fast-isel-abort=1 -mattr=+sign-ext,+simd128,+tail-call | FileCheck --check-prefixes=CHECK,FAST-TAIL %s
 
 ; Test that basic call operations assemble as expected.
 
 target triple = "wasm32-unknown-unknown"
 
 declare i32 @i32_nullary()

 ; CHECK-NEXT: call_indirect  $pop{{.*}}
 define void @call_indirect_alloca() {
 entry:
   %ptr = alloca i32, align 4
   call void %ptr()
   ret void
 }
 
+; Calling non-functional globals should be lowered to call_indirects.
+; CHECK-LABEL: call_indirect_int:
+; CHECK:      i32.const  $push[[L0:[0-9]+]]=, global_i8
+; CHECK-NEXT: call_indirect  $pop[[L0]]
+; CHECK-NEXT: i32.const  $push[[L1:[0-9]+]]=, global_i32
+; CHECK-NEXT: call_indirect  $pop[[L1]]
+@global_i8 = global i8 0
+@global_i32 = global i32 0
+define void @call_indirect_int() {
+  call void @global_i8()
+  call void @global_i32()
+  ret void
+}
+
+; Calling aliases of non-functional globals should be lowered to call_indirects.
+; CHECK-LABEL: call_indirect_int_alias:
+; CHECK:      i32.const  $push[[L0:[0-9]+]]=, global_i8_alias
+; CHECK-NEXT: call_indirect  $pop[[L0]]
+; CHECK-NEXT: i32.const  $push[[L1:[0-9]+]]=, global_i32_alias
+; CHECK-NEXT: call_indirect  $pop[[L1]]
+@global_i8_alias = alias i8, ptr @global_i8
+@global_i32_alias = alias i32, ptr @global_i32
+define void @call_indirect_int_alias() {
+  call void @global_i8_alias()
+  call void @global_i32_alias()
+  ret void
+}
+
+; Ideally calling aliases of functions should be lowered to direct calls. We
+; support this in the normal (=slow) isel.
+; CHECK-LABEL: call_func_alias:
+; SLOW:      call  func_alias
+; FAST:      i32.const  $push[[L0:[0-9]+]]=, func_alias
+; FAST-NEXT: call_indirect  $pop[[L0]]
+@func_alias = alias void (), ptr @call_void_nullary
+define void @call_func_alias() {
+  call void @func_alias()
+  ret void
+}
+
 ; TODO: test the following:
 ;  - More argument combinations.
 ;  - Tail call.
 ;  - Interesting returns (struct, multiple).
 ;  - Vararg.