[lld][WebAssembly] Honor requiredInBinary when combining data segments

In most circumstances BSS segments are not required in the output binary
but combineOutputSegments was erroneously including them.  This meant
that PIC binaries were including the BSS data as zero in the binary.

Fixes: emscripten-core/emscripten#23683

Author: sbc100

lld/test/wasm/data-segments.ll

@@ -17,6 +17,11 @@
 ; RUN: wasm-ld -mwasm64 -no-gc-sections --no-entry %t.bulk-mem64.o -o %t.bulk-mem64.wasm
 ; RUN: obj2yaml %t.bulk-mem64.wasm | FileCheck %s --check-prefixes ACTIVE,ACTIVE64
 
+;; In -pie mode segments are combined into one active segment.
+; RUN: wasm-ld --experimental-pic --import-memory -pie -no-gc-sections --no-entry %t.atomics.bulk-mem.pic.o -o %t.pic.wasm
+; RUN: obj2yaml %t.pic.wasm | FileCheck %s --check-prefixes ACTIVE-PIC
+; RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_init_memory --no-show-raw-insn --no-leading-addr %t.pic.wasm | FileCheck %s --check-prefixes PIC-NON-SHARED-DIS
+
 ;; atomics, bulk memory, shared memory => passive segments
 ; RUN: wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.o -o %t.atomics.bulk-mem.wasm
 ; RUN: obj2yaml %t.atomics.bulk-mem.wasm | FileCheck %s --check-prefix PASSIVE
@@ -28,9 +33,9 @@
 ; RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_init_memory --no-show-raw-insn --no-leading-addr %t.atomics.bulk-mem64.wasm | FileCheck %s --check-prefixes DIS,NOPIC-DIS -DPTR=i64
 
 ;; Also test in combination with PIC/pie
-; RUN: wasm-ld --experimental-pic -pie -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.pic.o -o %t.pic.wasm
-; RUN: obj2yaml %t.pic.wasm | FileCheck %s --check-prefixes PASSIVE-PIC,PASSIVE32-PIC
-; RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_init_memory --no-show-raw-insn --no-leading-addr %t.pic.wasm | FileCheck %s --check-prefixes DIS,PIC-DIS -DPTR=i32
+; RUN: wasm-ld --experimental-pic -pie -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.pic.o -o %t.shared.pic.wasm
+; RUN: obj2yaml %t.shared.pic.wasm | FileCheck %s --check-prefixes PASSIVE-PIC,PASSIVE32-PIC
+; RUN: llvm-objdump --disassemble-symbols=__wasm_call_ctors,__wasm_init_memory --no-show-raw-insn --no-leading-addr %t.shared.pic.wasm | FileCheck %s --check-prefixes DIS,PIC-DIS -DPTR=i32
 
 ;; Also test in combination with PIC/pie + wasm64
 ; RUN: wasm-ld -mwasm64 --experimental-pic -pie -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.pic-mem64.o -o %t.pic-mem64.wasm
@@ -47,7 +52,7 @@
 
 @g = thread_local global i32 99, align 4
 
-; ERROR: 'bulk-memory' feature must be used in order to use shared memory
+;; ERROR: 'bulk-memory' feature must be used in order to use shared memory
 
 ; ACTIVE-LABEL: - Type:            CODE
 ; ACTIVE-NEXT:    Functions:
@@ -76,6 +81,20 @@
 ; ACTIVE-NEXT:      - Index:           0
 ; ACTIVE-NEXT:        Name:            __wasm_call_ctors
 
+;; In ACTIVE-PIC mode the memory is imported which means all data segments
+;; (except BSS) are combined in the single one.
+;; BSS is not included here, and instead initialized using `memory.init` in
+;; `__wasm_init_memory`
+
+; ACTIVE-PIC:  - Type:            DATA
+; ACTIVE-PIC-NEXT:    Segments:
+; ACTIVE-PIC-NEXT:      - SectionOffset:   6
+; ACTIVE-PIC-NEXT:        InitFlags:       0
+; ACTIVE-PIC-NEXT:        Offset:
+; ACTIVE-PIC-NEXT:          Opcode:          GLOBAL_GET
+; ACTIVE-PIC-NEXT:          Index:           1
+; ACTIVE-PIC-NEXT:        Content:         63000000636F6E7374616E74000000002B00000068656C6C6F00676F6F646279650000002A000000
+
 ; PASSIVE-LABEL: - Type:            START
 ; PASSIVE-NEXT:    StartFunction:   2
 ; PASSIVE-LABEL: - Type:            DATACOUNT
@@ -151,6 +170,18 @@
 ; PASSIVE-PIC-NEXT:      - Index:           2
 ; PASSIVE-PIC-NEXT:        Name:            __wasm_init_memory
 
+;; For the non-shared PIC case the __wasm_init_memory only deals with BSS since
+;; all other segments are active
+; PIC-NON-SHARED-DIS:       <__wasm_init_memory>:
+; PIC-NON-SHARED-DIS-EMPTY:
+; PIC-NON-SHARED-DIS-NEXT:  i32.const	40
+; PIC-NON-SHARED-DIS-NEXT:  global.get	1
+; PIC-NON-SHARED-DIS-NEXT:  i32.add 
+; PIC-NON-SHARED-DIS-NEXT:  i32.const	0
+; PIC-NON-SHARED-DIS-NEXT:  i32.const	10000
+; PIC-NON-SHARED-DIS-NEXT:  memory.fill	0
+; PIC-NON-SHARED-DIS-NEXT:  end
+
 ;; no data relocations.
 ; DIS-LABEL:       <__wasm_call_ctors>:
 ; DIS-EMPTY:

lld/wasm/OutputSections.cpp

@@ -101,7 +101,8 @@ void DataSection::finalizeContents() {
   });
 #ifndef NDEBUG
   unsigned activeCount = llvm::count_if(segments, [](OutputSegment *segment) {
-    return (segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0;
+    return segment->requiredInBinary() &&
+           (segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0;
   });
 #endif
 

lld/wasm/Writer.cpp

@@ -1081,7 +1081,12 @@ void Writer::combineOutputSegments() {
     return;
   OutputSegment *combined = make<OutputSegment>(".data");
   combined->startVA = segments[0]->startVA;
+  std::vector<OutputSegment *> newSegments = {combined};
   for (OutputSegment *s : segments) {
+    if (!s->requiredInBinary()) {
+      newSegments.push_back(s);
+      continue;
+    }
     bool first = true;
     for (InputChunk *inSeg : s->inputSegments) {
       if (first)
@@ -1100,7 +1105,7 @@ void Writer::combineOutputSegments() {
     }
   }
 
-  segments = {combined};
+  segments = newSegments;
 }
 
 static void createFunction(DefinedFunction *func, StringRef bodyContent) {