[WebAssembly] Support binary generation for new EH

[aheejin]

This adds support for binary generation for the new EH proposal.

So far the only case that we emitted variable immediate operands in binary has been br_table's destinations. (Other variable_ops uses in TableGen files are register operands, such as the operands of call, so they don't get emitted in binary as a part of the same instruction.)

With this PR, variable immediate operands can include try_table's operands:

• The number of of catch clauses
• catch clauses sub-opcodes
  • catch: 0x00
  • catch_ref: 0x01
  • catch_all: 0x02
  • catch_all_ref: 0x03
• catch clauses' destinations

With try_table, we now have variable expr operands for try_table's catch clauses' tags. We treat their fixups in the same way we do for tags in other instructions such as in throw.

Diff without whitespace will be easier to view.

[llvmbot]

@llvm/pr-subscribers-mc

@llvm/pr-subscribers-backend-webassembly

Author: Heejin Ahn (aheejin)

Changes

This adds support for binary generation for the new EH proposal.

So far the only case that we emitted variable immediate operands in binary has been br_table's destinations. (Other variable_ops uses in TableGen files are register operands, such as the operands of call, so they don't get emitted in binary as a part of the same instruction.)

With this PR, variable immediate operands can include try_table's operands:

• The number of of catch clauses
• catch clauses sub-opcodes
  • catch: 0x00
  • catch_ref: 0x01
  • catch_all: 0x02
  • catch_all_ref: 0x03
• catch clauses' destinations

With try_table, we now have variable expr operands for try_table's catch clauses' tags. We treat their fixups in the same way we do for tags in other instructions such as in throw.

Diff without whitespace will be easier to view.

---

Full diff: https://github.com/llvm/llvm-project/pull/109027.diff

3 Files Affected:

• (modified) llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp (+41-29)
• (modified) llvm/test/CodeGen/WebAssembly/exception.ll (+1)
• (modified) llvm/test/MC/WebAssembly/eh-assembly.s (+2)

diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
index aaca213c4afe9b..3e7487dbd8f54e 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
@@ -82,14 +82,15 @@ void WebAssemblyMCCodeEmitter::encodeInstruction(
   // For br_table instructions, encode the size of the table. In the MCInst,
   // there's an index operand (if not a stack instruction), one operand for
   // each table entry, and the default operand.
-  if (MI.getOpcode() == WebAssembly::BR_TABLE_I32_S ||
-      MI.getOpcode() == WebAssembly::BR_TABLE_I64_S)
+  unsigned Opcode = MI.getOpcode();
+  if (Opcode == WebAssembly::BR_TABLE_I32_S ||
+      Opcode == WebAssembly::BR_TABLE_I64_S)
     encodeULEB128(MI.getNumOperands() - 1, OS);
-  if (MI.getOpcode() == WebAssembly::BR_TABLE_I32 ||
-      MI.getOpcode() == WebAssembly::BR_TABLE_I64)
+  if (Opcode == WebAssembly::BR_TABLE_I32 ||
+      Opcode == WebAssembly::BR_TABLE_I64)
     encodeULEB128(MI.getNumOperands() - 2, OS);
 
-  const MCInstrDesc &Desc = MCII.get(MI.getOpcode());
+  const MCInstrDesc &Desc = MCII.get(Opcode);
   for (unsigned I = 0, E = MI.getNumOperands(); I < E; ++I) {
     const MCOperand &MO = MI.getOperand(I);
     if (MO.isReg()) {
@@ -136,7 +137,12 @@ void WebAssemblyMCCodeEmitter::encodeInstruction(
           encodeULEB128(uint64_t(MO.getImm()), OS);
         }
       } else {
-        encodeULEB128(uint64_t(MO.getImm()), OS);
+        // Variadic immediate operands are br_table's destination operands or
+        // try_table's operands (# of catch clauses, catch sub-opcodes, or catch
+        // clause destinations)
+        assert(WebAssembly::isBrTable(Opcode) ||
+               Opcode == WebAssembly::TRY_TABLE_S);
+        encodeULEB128(uint32_t(MO.getImm()), OS);
       }
 
     } else if (MO.isSFPImm()) {
@@ -146,32 +152,38 @@ void WebAssemblyMCCodeEmitter::encodeInstruction(
       uint64_t D = MO.getDFPImm();
       support::endian::write<uint64_t>(OS, D, llvm::endianness::little);
     } else if (MO.isExpr()) {
-      const MCOperandInfo &Info = Desc.operands()[I];
       llvm::MCFixupKind FixupKind;
       size_t PaddedSize = 5;
-      switch (Info.OperandType) {
-      case WebAssembly::OPERAND_I32IMM:
-        FixupKind = MCFixupKind(WebAssembly::fixup_sleb128_i32);
-        break;
-      case WebAssembly::OPERAND_I64IMM:
-        FixupKind = MCFixupKind(WebAssembly::fixup_sleb128_i64);
-        PaddedSize = 10;
-        break;
-      case WebAssembly::OPERAND_FUNCTION32:
-      case WebAssembly::OPERAND_TABLE:
-      case WebAssembly::OPERAND_OFFSET32:
-      case WebAssembly::OPERAND_SIGNATURE:
-      case WebAssembly::OPERAND_TYPEINDEX:
-      case WebAssembly::OPERAND_GLOBAL:
-      case WebAssembly::OPERAND_TAG:
+      if (I < Desc.getNumOperands()) {
+        const MCOperandInfo &Info = Desc.operands()[I];
+        switch (Info.OperandType) {
+        case WebAssembly::OPERAND_I32IMM:
+          FixupKind = MCFixupKind(WebAssembly::fixup_sleb128_i32);
+          break;
+        case WebAssembly::OPERAND_I64IMM:
+          FixupKind = MCFixupKind(WebAssembly::fixup_sleb128_i64);
+          PaddedSize = 10;
+          break;
+        case WebAssembly::OPERAND_FUNCTION32:
+        case WebAssembly::OPERAND_TABLE:
+        case WebAssembly::OPERAND_OFFSET32:
+        case WebAssembly::OPERAND_SIGNATURE:
+        case WebAssembly::OPERAND_TYPEINDEX:
+        case WebAssembly::OPERAND_GLOBAL:
+        case WebAssembly::OPERAND_TAG:
+          FixupKind = MCFixupKind(WebAssembly::fixup_uleb128_i32);
+          break;
+        case WebAssembly::OPERAND_OFFSET64:
+          FixupKind = MCFixupKind(WebAssembly::fixup_uleb128_i64);
+          PaddedSize = 10;
+          break;
+        default:
+          llvm_unreachable("unexpected symbolic operand kind");
+        }
+      } else {
+        // Variadic expr operands are try_table's catch/catch_ref clauses' tags.
+        assert(Opcode == WebAssembly::TRY_TABLE_S);
         FixupKind = MCFixupKind(WebAssembly::fixup_uleb128_i32);
-        break;
-      case WebAssembly::OPERAND_OFFSET64:
-        FixupKind = MCFixupKind(WebAssembly::fixup_uleb128_i64);
-        PaddedSize = 10;
-        break;
-      default:
-        llvm_unreachable("unexpected symbolic operand kind");
       }
       Fixups.push_back(MCFixup::create(OS.tell() - Start, MO.getExpr(),
                                        FixupKind, MI.getLoc()));
diff --git a/llvm/test/CodeGen/WebAssembly/exception.ll b/llvm/test/CodeGen/WebAssembly/exception.ll
index 7259761d6313b6..1ad4c84f1c0237 100644
--- a/llvm/test/CodeGen/WebAssembly/exception.ll
+++ b/llvm/test/CodeGen/WebAssembly/exception.ll
@@ -1,6 +1,7 @@
 ; RUN: llc < %s -asm-verbose=false -wasm-enable-eh -exception-model=wasm -mattr=+exception-handling -wasm-enable-exnref -verify-machineinstrs | FileCheck --implicit-check-not=ehgcr -allow-deprecated-dag-overlap %s
 ; RUN: llc < %s -asm-verbose=false -wasm-enable-eh -exception-model=wasm -mattr=+exception-handling -wasm-enable-exnref -verify-machineinstrs -O0
 ; RUN: llc < %s -wasm-enable-eh -exception-model=wasm -mattr=+exception-handling -wasm-enable-exnref
+; RUN: llc < %s -wasm-enable-eh -exception-model=wasm -mattr=+exception-handling -wasm-enable-exnref -filetype=obj
 
 target triple = "wasm32-unknown-unknown"
 
diff --git a/llvm/test/MC/WebAssembly/eh-assembly.s b/llvm/test/MC/WebAssembly/eh-assembly.s
index a769bc447d0ba9..b4d6b324d96e3e 100644
--- a/llvm/test/MC/WebAssembly/eh-assembly.s
+++ b/llvm/test/MC/WebAssembly/eh-assembly.s
@@ -1,4 +1,6 @@
 # RUN: llvm-mc -triple=wasm32-unknown-unknown -mattr=+exception-handling --no-type-check < %s | FileCheck %s
+# Check that it converts to .o without errors, but don't check any output:
+# RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj -mattr=+exception-handling --no-type-check -o %t.o < %s
 
   .tagtype  __cpp_exception i32
   .tagtype  __c_longjmp i32