[WebAssembly] call_indirect issues table number relocs

If the reference-types feature is enabled, call_indirect will explicitly
reference its corresponding function table via `TABLE_NUMBER`
relocations against a table symbol.

Also, as before, address-taken functions can also cause the function
table to be created, only with reference-types they additionally cause a
symbol table entry to be emitted.

We abuse the used-in-reloc flag on symbols to indicate which tables
should end up in the symbol table.  We do this because unfortunately
older wasm-ld will carp if it see a table symbol.

Differential Revision: https://reviews.llvm.org/D90948

1 files changed, 13 insertions, 12 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
index 509f2be..d60c162 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyFastISel.cpp
@@ -869,19 +869,20 @@ bool WebAssemblyFastISel::selectCall(const Instruction *I) {
   if (IsDirect) {
     MIB.addGlobalAddress(Func);
   } else {
-    // Add placeholders for the type index and immediate flags
+    // Placehoder for the type index.
     MIB.addImm(0);
-    MIB.addImm(0);
-
-    // Ensure that the object file has a __indirect_function_table import, as we
-    // call_indirect against it.
-    MCSymbolWasm *Sym = WebAssembly::getOrCreateFunctionTableSymbol(
-        MF->getMMI().getContext(), "__indirect_function_table");
-    // Until call_indirect emits TABLE_NUMBER relocs against this symbol, mark
-    // it as NO_STRIP so as to ensure that the indirect function table makes it
-    // to linked output.
-    Sym->setNoStrip();
-
+    // The table into which this call_indirect indexes.
+    MCSymbolWasm *Table = WebAssembly::getOrCreateFunctionTableSymbol(
+        MF->getMMI().getContext(), Subtarget);
+    if (Subtarget->hasReferenceTypes()) {
+      MIB.addSym(Table);
+    } else {
+      // Otherwise for the MVP there is at most one table whose number is 0, but
+      // we can't write a table symbol or issue relocations.  Instead we just
+      // ensure the table is live.
+      Table->setNoStrip();
+      MIB.addImm(0);
+    }
     // See if we must truncate the function pointer.
     // CALL_INDIRECT takes an i32, but in wasm64 we represent function pointers
     // as 64-bit for uniformity with other pointer types.