[WebAssembly] Add isEHScopeReturn instruction property

Summary:
So far, `isReturn` property is used to mean both a return instruction
from a functon and the end of an EH scope, a scope that starts with a EH
scope entry BB and ends with a catchret or a cleanupret instruction.
Because WinEH uses funclets, all EH-scope-ending instructions are also
real return instruction from a function. But for wasm, they only serve
as the end marker of an EH scope but not a return instruction that
exits a function. This mismatch caused incorrect prolog and epilog
generation in wasm EH scopes. This patch fixes this.

This patch is in the same vein with rL333045, which splits
`MachineBasicBlock::isEHFuncletEntry` into `isEHFuncletEntry` and
`isEHScopeEntry`.

Reviewers: dschuff

Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D50653

llvm-svn: 340325

llvm/include/llvm/CodeGen/MachineBasicBlock.h

@@ -569,6 +569,12 @@ class MachineBasicBlock
     return !empty() && back().isReturn();
   }
 
+  /// Convenience function that returns true if the bock ends in a EH scope
+  /// return instruction.
+  bool isEHScopeReturnBlock() const {
+    return !empty() && back().isEHScopeReturn();
+  }
+
   /// Split the critical edge from this block to the given successor block, and
   /// return the newly created block, or null if splitting is not possible.
   ///

llvm/include/llvm/CodeGen/MachineInstr.h

@@ -616,6 +616,12 @@ class MachineInstr
     return hasProperty(MCID::Return, Type);
   }
 
+  /// Return true if this is an instruction that marks the end of an EH scope,
+  /// i.e., a catchpad or a cleanuppad instruction.
+  bool isEHScopeReturn(QueryType Type = AnyInBundle) const {
+    return hasProperty(MCID::EHScopeReturn, Type);
+  }
+
   bool isCall(QueryType Type = AnyInBundle) const {
     return hasProperty(MCID::Call, Type);
   }

llvm/include/llvm/MC/MCInstrDesc.h

@@ -120,6 +120,7 @@ enum Flag {
   HasOptionalDef,
   Pseudo,
   Return,
+  EHScopeReturn,
   Call,
   Barrier,
   Terminator,

llvm/include/llvm/Target/Target.td

@@ -439,6 +439,7 @@ class Instruction {
   // instruction.
   bit isReturn     = 0;     // Is this instruction a return instruction?
   bit isBranch     = 0;     // Is this instruction a branch instruction?
+  bit isEHScopeReturn = 0;  // Does this instruction end an EH scope?
   bit isIndirectBranch = 0; // Is this instruction an indirect branch?
   bit isCompare    = 0;     // Is this instruction a comparison instruction?
   bit isMoveImm    = 0;     // Is this instruction a move immediate instruction?

llvm/lib/CodeGen/Analysis.cpp

@@ -650,7 +650,7 @@ static void collectEHScopeMembers(
 
     // Returns are boundaries where scope transfer can occur, don't follow
     // successors.
-    if (Visiting->isReturnBlock())
+    if (Visiting->isEHScopeReturnBlock())
       continue;
 
     for (const MachineBasicBlock *Succ : Visiting->successors())

llvm/lib/Target/WebAssembly/WebAssemblyInstrControl.td

@@ -185,10 +185,8 @@ defm CATCH_ALL : NRI<(outs), (ins), [], "catch_all", 0x05>;
 }
 
 // Pseudo instructions: cleanupret / catchret
-// They are not return instructions in wasm, but setting 'isReturn' to true as
-// in X86 is necessary for computing EH scope membership.
 let isTerminator = 1, hasSideEffects = 1, isBarrier = 1, hasCtrlDep = 1,
-    isCodeGenOnly = 1, isReturn = 1 in {
+    isCodeGenOnly = 1, isEHScopeReturn = 1 in {
   defm CLEANUPRET : NRI<(outs), (ins), [(cleanupret)], "", 0>;
   defm CATCHRET : NRI<(outs), (ins bb_op:$dst, bb_op:$from),
                    [(catchret bb:$dst, bb:$from)], "", 0>;

llvm/lib/Target/X86/X86InstrCompiler.td

@@ -178,7 +178,7 @@ def EH_RETURN64   : I<0xC3, RawFrm, (outs), (ins GR64:$addr),
 }
 
 let isTerminator = 1, hasSideEffects = 1, isBarrier = 1, hasCtrlDep = 1,
-    isCodeGenOnly = 1, isReturn = 1 in {
+    isCodeGenOnly = 1, isReturn = 1, isEHScopeReturn = 1 in {
   def CLEANUPRET : I<0, Pseudo, (outs), (ins), "# CLEANUPRET", [(cleanupret)]>;
 
   // CATCHRET needs a custom inserter for SEH.

llvm/test/CodeGen/WebAssembly/exception.ll

@@ -150,7 +150,71 @@ terminate10:                                      ; preds = %ehcleanup7
   unreachable
 }
 
+; Tests prologues and epilogues are not generated within EH scopes.
+; They should not be treated as funclets; BBs starting with a catch instruction
+; should not have a prologue, and BBs ending with a catchret/cleanupret should
+; not have an epilogue. This is separate from __stack_pointer restoring
+; instructions after a catch instruction.
+
+; CHECK-LABEL: test_no_prolog_epilog_in_ehpad
+; CHECK:  try
+; CHECK:  call      foo@FUNCTION
+; CHECK:  i32.catch
+; CHECK-NOT:  get_global  $push{{.+}}=, __stack_pointer@GLOBAL
+; CHECK:  try
+; CHECK:  call      foo@FUNCTION
+; CHECK:  catch_all
+; TODO This should be removed too in a later patch
+; CHECK-NO T:  get_global  $push{{.+}}=, __stack_pointer@GLOBAL
+; CHECK:  call      __cxa_end_catch@FUNCTION
+; CHECK-NOT:  set_global  __stack_pointer@GLOBAL, $pop{{.+}}
+; CHECK:  end_try
+; CHECK-NOT:  set_global  __stack_pointer@GLOBAL, $pop{{.+}}
+; CHECK:  end_try
+define void @test_no_prolog_epilog_in_ehpad() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+entry:
+  %stack_var = alloca i32, align 4
+  call void @bar(i32* %stack_var)
+  invoke void @foo()
+          to label %try.cont unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %entry
+  %0 = catchswitch within none [label %catch.start] unwind to caller
+
+catch.start:                                      ; preds = %catch.dispatch
+  %1 = catchpad within %0 [i8* bitcast (i8** @_ZTIi to i8*)]
+  %2 = call i8* @llvm.wasm.get.exception(token %1)
+  %3 = call i32 @llvm.wasm.get.ehselector(token %1)
+  %4 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIi to i8*))
+  %matches = icmp eq i32 %3, %4
+  br i1 %matches, label %catch, label %rethrow
+
+catch:                                            ; preds = %catch.start
+  %5 = call i8* @__cxa_begin_catch(i8* %2) [ "funclet"(token %1) ]
+  %6 = bitcast i8* %5 to float*
+  %7 = load float, float* %6, align 4
+  invoke void @foo() [ "funclet"(token %1) ]
+          to label %invoke.cont1 unwind label %ehcleanup
+
+invoke.cont1:                                     ; preds = %catch
+  call void @__cxa_end_catch() [ "funclet"(token %1) ]
+  catchret from %1 to label %try.cont
+
+rethrow:                                          ; preds = %catch.start
+  call void @__cxa_rethrow() [ "funclet"(token %1) ]
+  unreachable
+
+try.cont:                                         ; preds = %entry, %invoke.cont1
+  ret void
+
+ehcleanup:                                        ; preds = %catch
+  %8 = cleanuppad within %1 []
+  call void @__cxa_end_catch() [ "funclet"(token %8) ]
+  cleanupret from %8 unwind to caller
+}
+
 declare void @foo()
+declare void @bar(i32*)
 declare i32 @__gxx_wasm_personality_v0(...)
 declare i8* @llvm.wasm.get.exception(token)
 declare i32 @llvm.wasm.get.ehselector(token)

llvm/utils/TableGen/CodeGenInstruction.cpp

@@ -302,6 +302,7 @@ CodeGenInstruction::CodeGenInstruction(Record *R)
   AsmString = R->getValueAsString("AsmString");
 
   isReturn     = R->getValueAsBit("isReturn");
+  isEHScopeReturn = R->getValueAsBit("isEHScopeReturn");
   isBranch     = R->getValueAsBit("isBranch");
   isIndirectBranch = R->getValueAsBit("isIndirectBranch");
   isCompare    = R->getValueAsBit("isCompare");

llvm/utils/TableGen/CodeGenInstruction.h

@@ -222,6 +222,7 @@ template <typename T> class ArrayRef;
 
     // Various boolean values we track for the instruction.
     bool isReturn : 1;
+    bool isEHScopeReturn : 1;
     bool isBranch : 1;
     bool isIndirectBranch : 1;
     bool isCompare : 1;

llvm/utils/TableGen/InstrDocsEmitter.cpp

@@ -100,6 +100,7 @@ void EmitInstrDocs(RecordKeeper &RK, raw_ostream &OS) {
 #define str(s) #s
 #define FLAG(f) if (II->f) { FlagStrings.push_back(str(f)); }
     FLAG(isReturn)
+    FLAG(isEHScopeReturn)
     FLAG(isBranch)
     FLAG(isIndirectBranch)
     FLAG(isCompare)

llvm/utils/TableGen/InstrInfoEmitter.cpp

@@ -569,6 +569,7 @@ void InstrInfoEmitter::emitRecord(const CodeGenInstruction &Inst, unsigned Num,
   // Emit all of the target independent flags...
   if (Inst.isPseudo)           OS << "|(1ULL<<MCID::Pseudo)";
   if (Inst.isReturn)           OS << "|(1ULL<<MCID::Return)";
+  if (Inst.isEHScopeReturn)    OS << "|(1ULL<<MCID::EHScopeReturn)";
   if (Inst.isBranch)           OS << "|(1ULL<<MCID::Branch)";
   if (Inst.isIndirectBranch)   OS << "|(1ULL<<MCID::IndirectBranch)";
   if (Inst.isCompare)          OS << "|(1ULL<<MCID::Compare)";