[WebAssembly] Handle symbols in .init_array sections (#119127)

Follow on from #111008.

(cherry picked from commit ed91843)

Author: georgestagg

llvm/lib/MC/WasmObjectWriter.cpp

@@ -1326,6 +1326,22 @@ static bool isInSymtab(const MCSymbolWasm &Sym) {
   return true;
 }
 
+static bool isSectionReferenced(MCAssembler &Asm, MCSectionWasm &Section) {
+  StringRef SectionName = Section.getName();
+
+  for (const MCSymbol &S : Asm.symbols()) {
+    const auto &WS = static_cast<const MCSymbolWasm &>(S);
+    if (WS.isData() && WS.isInSection()) {
+      auto &RefSection = static_cast<MCSectionWasm &>(WS.getSection());
+      if (RefSection.getName() == SectionName) {
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
 void WasmObjectWriter::prepareImports(
     SmallVectorImpl<wasm::WasmImport> &Imports, MCAssembler &Asm) {
   // For now, always emit the memory import, since loads and stores are not
@@ -1482,8 +1498,10 @@ uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm,
     LLVM_DEBUG(dbgs() << "Processing Section " << SectionName << "  group "
                       << Section.getGroup() << "\n";);
 
-    // .init_array sections are handled specially elsewhere.
-    if (SectionName.starts_with(".init_array"))
+    // .init_array sections are handled specially elsewhere, include them in
+    // data segments if and only if referenced by a symbol.
+    if (SectionName.starts_with(".init_array") &&
+        !isSectionReferenced(Asm, Section))
       continue;
 
     // Code is handled separately

llvm/test/MC/WebAssembly/init-array-label.s

@@ -0,0 +1,91 @@
+# RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj < %s | obj2yaml | FileCheck %s
+
+init1:
+	.functype	init1 () -> ()
+	end_function
+
+init2:
+	.functype	init2 () -> ()
+	end_function
+
+	.section	.init_array.42,"",@
+	.p2align	2, 0x0
+	.int32	init1
+
+	.section	.init_array,"",@
+	.globl	p_init1
+	.p2align	2, 0x0
+p_init1:
+	.int32	init1
+	.size	p_init1, 4
+
+	.section	.init_array,"",@
+	.globl	p_init2
+	.p2align	2, 0x0
+p_init2:
+	.int32	init1
+	.int32	init2
+	.size	p_init2, 8
+
+# CHECK:        - Type:            FUNCTION
+# CHECK-NEXT:     FunctionTypes:   [ 0, 0 ]
+# CHECK-NEXT:   - Type:            DATACOUNT
+# CHECK-NEXT:     Count:           1
+# CHECK-NEXT:   - Type:            CODE
+# CHECK-NEXT:     Functions:
+# CHECK-NEXT:       - Index:           0
+# CHECK-NEXT:         Locals:          []
+# CHECK-NEXT:         Body:            0B
+# CHECK-NEXT:       - Index:           1
+# CHECK-NEXT:         Locals:          []
+# CHECK-NEXT:         Body:            0B
+# CHECK-NEXT:   - Type:            DATA
+# CHECK-NEXT:     Segments:
+# CHECK-NEXT:       - SectionOffset:   6
+# CHECK-NEXT:         InitFlags:       0
+# CHECK-NEXT:         Offset:
+# CHECK-NEXT:           Opcode:          I32_CONST
+# CHECK-NEXT:           Value:           0
+# CHECK-NEXT:         Content:         '000000000000000000000000'
+# CHECK-NEXT:   - Type:            CUSTOM
+# CHECK-NEXT:     Name:            linking
+# CHECK-NEXT:     Version:         2
+# CHECK-NEXT:     SymbolTable:
+# CHECK-NEXT:       - Index:           0
+# CHECK-NEXT:         Kind:            FUNCTION
+# CHECK-NEXT:         Name:            init1
+# CHECK-NEXT:         Flags:           [ BINDING_LOCAL ]
+# CHECK-NEXT:         Function:        0
+# CHECK-NEXT:       - Index:           1
+# CHECK-NEXT:         Kind:            FUNCTION
+# CHECK-NEXT:         Name:            init2
+# CHECK-NEXT:         Flags:           [ BINDING_LOCAL ]
+# CHECK-NEXT:         Function:        1
+# CHECK-NEXT:       - Index:           2
+# CHECK-NEXT:         Kind:            DATA
+# CHECK-NEXT:         Name:            p_init1
+# CHECK-NEXT:         Flags:           [  ]
+# CHECK-NEXT:         Segment:         0
+# CHECK-NEXT:         Size:            4
+# CHECK-NEXT:       - Index:           3
+# CHECK-NEXT:         Kind:            DATA
+# CHECK-NEXT:         Name:            p_init2
+# CHECK-NEXT:         Flags:           [  ]
+# CHECK-NEXT:         Segment:         0
+# CHECK-NEXT:         Offset:          4
+# CHECK-NEXT:         Size:            8
+# CHECK-NEXT:     SegmentInfo:
+# CHECK-NEXT:       - Index:           0
+# CHECK-NEXT:         Name:            .init_array
+# CHECK-NEXT:         Alignment:       2
+# CHECK-NEXT:         Flags:           [  ]
+# CHECK-NEXT:     InitFunctions:
+# CHECK-NEXT:       - Priority:        42
+# CHECK-NEXT:         Symbol:          0
+# CHECK-NEXT:       - Priority:        65535
+# CHECK-NEXT:         Symbol:          0
+# CHECK-NEXT:       - Priority:        65535
+# CHECK-NEXT:         Symbol:          0
+# CHECK-NEXT:       - Priority:        65535
+# CHECK-NEXT:         Symbol:          1
+# CHECK-NEXT: ...