[WebAssembly] Make segment/size/type directives optional in asm

Summary:
These were "boilerplate" that repeated information already present
in .functype and end_function, that needed to be repeated to Please
the particular way our object writing works, and missing them would
generate errors.

Instead, we generate the information for these automatically so the
user can concern itself with writing more canonical wasm functions
that always work as expected.

Reviewers: dschuff, sbc100

Subscribers: jgravelle-google, aheejin, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D57546

llvm-svn: 353067

llvm/lib/MC/MCParser/WasmAsmParser.cpp

@@ -91,8 +91,11 @@ public:
         Expect(AsmToken::Comma, ",") || Expect(AsmToken::At, "@") ||
         Expect(AsmToken::EndOfStatement, "eol"))
       return true;
-    auto WS = getContext().getWasmSection(Name, SectionKind::getText());
-    getStreamer().SwitchSection(WS);
+    // This is done automatically by the assembler for text sections currently,
+    // so we don't need to emit that here. This is what it would do (and may
+    // be needed later for other section types):
+    // auto WS = getContext().getWasmSection(Name, SectionKind::getText());
+    // getStreamer().SwitchSection(WS);
     return false;
   }
 
@@ -110,8 +113,10 @@ public:
       return true;
     if (Expect(AsmToken::EndOfStatement, "eol"))
       return true;
-    // MCWasmStreamer implements this.
-    getStreamer().emitELFSize(Sym, Expr);
+    // This is done automatically by the assembler for functions currently,
+    // so we don't need to emit that here. This is what it would do:
+    (void)Sym;
+    // getStreamer().emitELFSize(Sym, Expr);
     return false;
   }
 

llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp

@@ -17,10 +17,12 @@
 #include "MCTargetDesc/WebAssemblyTargetStreamer.h"
 #include "WebAssembly.h"
 #include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCParser/MCParsedAsmOperand.h"
 #include "llvm/MC/MCParser/MCTargetAsmParser.h"
+#include "llvm/MC/MCSectionWasm.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/MC/MCSymbol.h"
@@ -169,6 +171,7 @@ class WebAssemblyAsmParser final : public MCTargetAsmParser {
     FunctionStart,
     FunctionLocals,
     Instructions,
+    EndFunction,
   } CurrentState = FileStart;
 
   // For ensuring blocks are properly nested.
@@ -186,6 +189,7 @@ class WebAssemblyAsmParser final : public MCTargetAsmParser {
   // We track this to see if a .functype following a label is the same,
   // as this is how we recognize the start of a function.
   MCSymbol *LastLabel = nullptr;
+  MCSymbol *LastFunctionLabel = nullptr;
 
 public:
   WebAssemblyAsmParser(const MCSubtargetInfo &STI, MCAsmParser &Parser,
@@ -445,6 +449,7 @@ public:
       if (pop(BaseName, Block))
         return true;
     } else if (BaseName == "end_function") {
+      CurrentState = EndFunction;
       if (pop(BaseName, Function) || ensureEmptyNestingStack())
         return true;
     }
@@ -604,6 +609,7 @@ public:
         if (ensureEmptyNestingStack())
           return true;
         CurrentState = FunctionStart;
+        LastFunctionLabel = LastLabel;
         push(Function);
       }
       auto Signature = make_unique<wasm::WasmSignature>();
@@ -666,8 +672,12 @@ public:
             *Out.getTargetStreamer());
         TOut.emitLocal(SmallVector<wasm::ValType, 0>());
       }
-      CurrentState = Instructions;
       Out.EmitInstruction(Inst, getSTI());
+      if (CurrentState == EndFunction) {
+        onEndOfFunction();
+      } else {
+        CurrentState = Instructions;
+      }
       return false;
     }
     case Match_MissingFeature:
@@ -693,6 +703,30 @@ public:
     llvm_unreachable("Implement any new match types added!");
   }
 
+  void doBeforeLabelEmit(MCSymbol *Symbol) override {
+    // Start a new section for the next function automatically, since our
+    // object writer expects each function to have its own section. This way
+    // The user can't forget this "convention".
+    auto SymName = Symbol->getName();
+    if (SymName.startswith(".L"))
+      return; // Local Symbol.
+    auto SecName = ".text." + SymName;
+    auto WS = getContext().getWasmSection(SecName, SectionKind::getText());
+    getStreamer().SwitchSection(WS);
+  }
+
+  void onEndOfFunction() {
+    // Automatically output a .size directive, so it becomes optional for the
+    // user.
+    auto TempSym = getContext().createLinkerPrivateTempSymbol();
+    getStreamer().EmitLabel(TempSym);
+    auto Start = MCSymbolRefExpr::create(LastLabel, getContext());
+    auto End = MCSymbolRefExpr::create(TempSym, getContext());
+    auto Expr =
+        MCBinaryExpr::create(MCBinaryExpr::Sub, End, Start, getContext());
+    getStreamer().emitELFSize(LastFunctionLabel, Expr);
+  }
+
   void onEndOfFile() override { ensureEmptyNestingStack(); }
 };
 } // end anonymous namespace

llvm/test/MC/WebAssembly/assembler-binary.ll

@@ -28,8 +28,6 @@ entry:
 ; ASM-NEXT: 	.functype	foo (i32) -> ()
 ; ASM-NEXT: 	call	bar@FUNCTION
 ; ASM-NEXT: 	end_function
-; ASM-NEXT: .Lfunc_end0:
-; ASM-NEXT: 	.size	foo, .Lfunc_end0-foo
 ; ASM:       	.functype	bar () -> ()
 
 

llvm/test/MC/WebAssembly/basic-assembly-errors.s

@@ -1,8 +1,5 @@
 # RUN: not llvm-mc -triple=wasm32-unknown-unknown -mattr=+simd128,+nontrapping-fptoint,+exception-handling < %s 2>&1 | FileCheck %s
 
-    .text
-    .section    .text.main,"",@
-    .type       test0,@function
 # CHECK: End of block construct with no start: end_try
     end_try
 test0:
@@ -20,6 +17,4 @@ test0:
 # CHECK: error: Unmatched block construct(s) at function end: block
 # CHECK: error: Unmatched block construct(s) at function end: function
     end_function
-.Lfunc_end0:
-    .size       test0, .Lfunc_end0-test0
 

llvm/test/MC/WebAssembly/basic-assembly.s

@@ -2,9 +2,6 @@
 # this one is just here to see if it converts to .o without errors, but doesn't check any output:
 # RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj -mattr=+unimplemented-simd128,+nontrapping-fptoint,+exception-handling < %s
 
-    .text
-    .section .text.main,"",@
-    .type    test0,@function
 test0:
     # Test all types:
     .functype   test0 (i32, i64) -> (i32)
@@ -86,8 +83,6 @@ test0:
     #i32.trunc_sat_f32_s
     global.get  __stack_pointer@GLOBAL
     end_function
-.Lfunc_end0:
-    .size	test0, .Lfunc_end0-test0
     .globaltype	__stack_pointer, i32
 
 # CHECK:           .text

llvm/test/MC/WebAssembly/objdump.s

@@ -1,25 +1,17 @@
 # RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj -o %t.o -mattr=+simd128,+nontrapping-fptoint,+exception-handling < %s
 # RUN: llvm-objdump -triple=wasm32-unknown-unknown -disassemble %t.o | FileCheck %s
 
-    .section .text.main1,"",@
-    .type    test0,@function
 test0:
     .functype   test0 (i32, i64) -> (i32)
     .local      f32, f64, v128, v128
     local.get   2
     end_function
-.Lfunc_end0:
-    .size	test0, .Lfunc_end0-test0
 
-    .section .text.main2,"",@
-    .type    test1,@function
 test1:
     .functype   test1 (i32, i64) -> (i32)
     .local      i32, i64, except_ref
     local.get   3
     end_function
-.Lfunc_end1:
-    .size	test1, .Lfunc_end1-test1
 
 
 # CHECK-LABEL: CODE: