[WebAssembly] Disable offset folding for function addresses

Wasm does not support function addresses with offsets, but isel can
generate folded SDValues in the form of (@func + offset) without this
patch.

Fixes https://bugs.llvm.org/show_bug.cgi?id=43133.

Reviewed By: dschuff, sbc100

Differential Revision: https://reviews.llvm.org/D107940

llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp

@@ -770,6 +770,13 @@ bool WebAssemblyTargetLowering::isVectorLoadExtDesirable(SDValue ExtVal) const {
          (ExtT == MVT::v2i64 && MemT == MVT::v2i32);
 }
 
+bool WebAssemblyTargetLowering::isOffsetFoldingLegal(
+    const GlobalAddressSDNode *GA) const {
+  // Wasm doesn't support function addresses with offsets
+  const GlobalValue *GV = GA->getGlobal();
+  return isa<Function>(GV) ? false : TargetLowering::isOffsetFoldingLegal(GA);
+}
+
 EVT WebAssemblyTargetLowering::getSetCCResultType(const DataLayout &DL,
                                                   LLVMContext &C,
                                                   EVT VT) const {

llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.h

@@ -102,6 +102,7 @@ class WebAssemblyTargetLowering final : public TargetLowering {
                                       bool *Fast) const override;
   bool isIntDivCheap(EVT VT, AttributeList Attr) const override;
   bool isVectorLoadExtDesirable(SDValue ExtVal) const override;
+  bool isOffsetFoldingLegal(const GlobalAddressSDNode *GA) const override;
   EVT getSetCCResultType(const DataLayout &DL, LLVMContext &Context,
                          EVT VT) const override;
   bool getTgtMemIntrinsic(IntrinsicInfo &Info, const CallInst &I,

llvm/test/CodeGen/WebAssembly/function-addr-offset.ll

@@ -0,0 +1,35 @@
+; RUN: llc < %s -verify-machineinstrs | FileCheck %s
+
+; Wasm does not currently support function addresses with offsets, so we
+; shouldn't try to create a folded SDNode like (function + offset). This is a
+; regression test for the folding bug and this should not crash in MCInstLower.
+
+target triple = "wasm32-unknown-unknown"
+
+; 'hidden' here should be present to reproduce the bug
+declare hidden void @ham(i8*)
+
+define void @bar(i8* %ptr) {
+bb1:
+  br i1 undef, label %bb3, label %bb2
+
+bb2:
+  ; While lowering this switch, isel creates (@ham + 1) expression as a course
+  ; of range optimization for switch, and tries to fold the expression, but
+  ; wasm does not support with function addresses with offsets. This folding
+  ; should be disabled.
+  ; CHECK:      i32.const  ham
+  ; CHECK-NEXT: i32.const  1
+  ; CHECK-NEXT: i32.add
+  switch i32 ptrtoint (void (i8*)* @ham to i32), label %bb4 [
+    i32 -1, label %bb3
+    i32 0, label %bb3
+  ]
+
+bb3:
+  unreachable
+
+bb4:
+  %tmp = load i8, i8* %ptr
+  unreachable
+}