Partial support for common linkage for WebAssembly

llvm/lib/MC/MCWasmStreamer.cpp

@@ -14,6 +14,7 @@
 #include "llvm/MC/MCAsmBackend.h"
 #include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCCodeEmitter.h"
+#include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCFixup.h"
 #include "llvm/MC/MCObjectStreamer.h"
@@ -131,7 +132,29 @@ bool MCWasmStreamer::emitSymbolAttribute(MCSymbol *S, MCSymbolAttr Attribute) {
 
 void MCWasmStreamer::emitCommonSymbol(MCSymbol *S, uint64_t Size,
                                       Align ByteAlignment) {
-  llvm_unreachable("Common symbols are not yet implemented for Wasm");
+  auto *Symbol = cast<MCSymbolWasm>(S);
+
+  pushSection();
+
+  // Common symbols are very close to weak symbols, so manually build a weak
+  // symbol.
+  MCSectionWasm *SW = getContext().getWasmSection(".bss.common." + S->getName(),
+                                                  SectionKind::getData());
+  SW->setAlignment(ByteAlignment);
+  getAssembler().registerSection(*SW);
+
+  switchSection(SW);
+
+  MCFragment *F = getCurrentFragment();
+  F->appendContents(Size, '\0');
+  Symbol->setFragment(F);
+
+  Symbol->setSize(MCConstantExpr::create(Size, getContext(), false, 8));
+  Symbol->setWeak(true);
+  Symbol->setExternal(true);
+  getAssembler().registerSymbol(*Symbol);
+
+  popSection();
 }
 
 void MCWasmStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {

llvm/test/MC/WebAssembly/common.ll

@@ -0,0 +1,69 @@
+; RUN; llc -mcpu=mvp -filetype=obj %s -o - | obj2yaml | FileCheck %s
+; RUN; llc -mcpu=mvp -filetype=asm %s -asm-verbose=false -o -  | FileCheck --check-prefix=ASM %s
+; RUN: llc -mcpu=mvp -filetype=asm %s -o - | llvm-mc -triple=wasm32 -filetype=obj  -o - | obj2yaml | FileCheck %s
+
+target triple = "wasm32-unknown-unknown"
+;target triple = "x86_64-redhat-linux-gnu"
+@b = common dso_local global [10 x i32] zeroinitializer, align 4
+@c = common dso_local global [20 x i32] zeroinitializer, align 32
+
+; CHECK-ASM: .file	"common.ll"
+; CHECK-ASM: .type	b,@object
+; CHECK-ASM: .comm	b,40,2
+; CHECK-ASM: .type	c,@object
+; CHECK-ASM: .comm	c,80,5
+
+
+; CHECK:      --- !WASM
+; CHECK-NEXT: FileHeader:
+; CHECK-NEXT:   Version:         0x1
+; CHECK-NEXT: Sections:
+; CHECK-NEXT:   - Type:            IMPORT
+; CHECK-NEXT:     Imports:
+; CHECK-NEXT:       - Module:          env
+; CHECK-NEXT:         Field:           __linear_memory
+; CHECK-NEXT:         Kind:            MEMORY
+; CHECK-NEXT:         Memory:
+; CHECK-NEXT:           Minimum:         0x1
+; CHECK-NEXT:   - Type:            DATACOUNT
+; CHECK-NEXT:     Count:           2
+; 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:         '00000000000000000000000000000000000000000000000000000000000000000000000000000000'
+; CHECK-NEXT:       - SectionOffset:   52
+; CHECK-NEXT:         InitFlags:       0
+; CHECK-NEXT:         Offset:
+; CHECK-NEXT:           Opcode:          I32_CONST
+; CHECK-NEXT:           Value:           64
+; CHECK-NEXT:         Content:         '0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000'
+; CHECK-NEXT:   - Type:            CUSTOM
+; CHECK-NEXT:     Name:            linking
+; CHECK-NEXT:     Version:         2
+; CHECK-NEXT:     SymbolTable:
+; CHECK-NEXT:       - Index:           0
+; CHECK-NEXT:         Kind:            DATA
+; CHECK-NEXT:         Name:            b
+; CHECK-NEXT:         Flags:           [ BINDING_WEAK ]
+; CHECK-NEXT:         Segment:         0
+; CHECK-NEXT:         Size:            40
+; CHECK-NEXT:       - Index:           1
+; CHECK-NEXT:         Kind:            DATA
+; CHECK-NEXT:         Name:            c
+; CHECK-NEXT:         Flags:           [ BINDING_WEAK ]
+; CHECK-NEXT:         Segment:         1
+; CHECK-NEXT:         Size:            80
+; CHECK-NEXT:     SegmentInfo:
+; CHECK-NEXT:       - Index:           0
+; CHECK-NEXT:         Name:            .bss.common.b
+; CHECK-NEXT:         Alignment:       2
+; CHECK-NEXT:         Flags:           [  ]
+; CHECK-NEXT:       - Index:           1
+; CHECK-NEXT:         Name:            .bss.common.c
+; CHECK-NEXT:         Alignment:       5
+; CHECK-NEXT:         Flags:           [  ]
+; CHECK-NEXT: ...