[llvm] [WebAssembly] Fix lowering of (extending) loads from addrspace(1) globals (PR #155937)

[via llvm-commits]

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@@ -1764,16 +1781,119 @@ SDValue WebAssemblyTargetLowering::LowerLoad(SDValue Op,
   LoadSDNode *LN = cast<LoadSDNode>(Op.getNode());
   const SDValue &Base = LN->getBasePtr();
   const SDValue &Offset = LN->getOffset();
+  ISD::LoadExtType ExtType = LN->getExtensionType();
+  EVT ResultType = LN->getValueType(0);
 
   if (IsWebAssemblyGlobal(Base)) {
     if (!Offset->isUndef())
       report_fatal_error(
           "unexpected offset when loading from webassembly global", false);
 
-    SDVTList Tys = DAG.getVTList(LN->getValueType(0), MVT::Other);
-    SDValue Ops[] = {LN->getChain(), Base};
-    return DAG.getMemIntrinsicNode(WebAssemblyISD::GLOBAL_GET, DL, Tys, Ops,
-                                   LN->getMemoryVT(), LN->getMemOperand());
+    if (!ResultType.isInteger() && !ResultType.isFloatingPoint()) {
+      SDVTList Tys = DAG.getVTList(ResultType, MVT::Other);
+      SDValue Ops[] = {LN->getChain(), Base};
+      SDValue GlobalGetNode =
+          DAG.getMemIntrinsicNode(WebAssemblyISD::GLOBAL_GET, DL, Tys, Ops,
+                                  LN->getMemoryVT(), LN->getMemOperand());
+      return GlobalGetNode;
+    }
+
+    EVT GT = MVT::INVALID_SIMPLE_VALUE_TYPE;
+
+    if (const GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(Base))
+      GT = EVT::getEVT(GA->getGlobal()->getValueType());
+    if (Base->getOpcode() == WebAssemblyISD::Wrapper)
+      if (const GlobalAddressSDNode *GA =
+              dyn_cast<GlobalAddressSDNode>(Base->getOperand(0)))
+        GT = EVT::getEVT(GA->getGlobal()->getValueType());
+
+    if (GT != MVT::i8 && GT != MVT::i16 && GT != MVT::i32 && GT != MVT::i64 &&
+        GT != MVT::f32 && GT != MVT::f64)
+      report_fatal_error("encountered unexpected global type for Base when "
+                         "loading from webassembly global",
+                         false);
+
+    EVT PromotedGT = (GT == MVT::i8 || GT == MVT::i16) ? MVT::i32 : GT;
+
+    if (ExtType == ISD::NON_EXTLOAD) {
+      // A normal, non-extending load may try to load more or less than the
+      // underlying global, which is invalid. We lower this to a load of the
+      // global (i32 or i64) then truncate or extend as needed
+
+      // Modify the MMO to load the full global
+      MachineMemOperand *OldMMO = LN->getMemOperand();
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QuantumSegfault wrote:

So is this the correct approach (and worth making into a helper)? I wasn't sure whether or not it's safe to modify the existing MMO, so I figured I better clone it.

Otherwise, I could call `MachineMemOperand::setType` on the existing MMO.

https://github.com/llvm/llvm-project/pull/155937