Ensure NoTrapAfterNoreturn is false for the wasm backend (#65876)

In the WebAssembly back end, the TrapUnreachable option is currently
load-bearing for correctness, inserting wasm `unreachable` instructions
where needed to create valid wasm. There is another option,
NoTrapAfterNoreturn, that removes some of those traps and causes
incorrect wasm to be emitted.

This turns off `NoTrapAfterNoreturn` for the Wasm backend and adds new   
tests.

Author: majaha

llvm/include/llvm/CodeGen/MachineFunction.h

@@ -266,7 +266,7 @@ class LLVM_EXTERNAL_VISIBILITY MachineFunction {
   // RegInfo - Information about each register in use in the function.
   MachineRegisterInfo *RegInfo;
 
-  // Used to keep track of target-specific per-machine function information for
+  // Used to keep track of target-specific per-machine-function information for
   // the target implementation.
   MachineFunctionInfo *MFInfo;
 

llvm/include/llvm/CodeGen/MachineInstr.h

@@ -1276,7 +1276,7 @@ class MachineInstr
   /// eraseFromBundle() to erase individual bundled instructions.
   void eraseFromParent();
 
-  /// Unlink 'this' form its basic block and delete it.
+  /// Unlink 'this' from its basic block and delete it.
   ///
   /// If the instruction is part of a bundle, the other instructions in the
   /// bundle remain bundled.

llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp

@@ -667,7 +667,7 @@ void WebAssemblyCFGStackify::removeUnnecessaryInstrs(MachineFunction &MF) {
 
   // When there is an unconditional branch right before a catch instruction and
   // it branches to the end of end_try marker, we don't need the branch, because
-  // it there is no exception, the control flow transfers to that point anyway.
+  // if there is no exception, the control flow transfers to that point anyway.
   // bb0:
   //   try
   //     ...

llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp

@@ -127,6 +127,7 @@ WebAssemblyTargetMachine::WebAssemblyTargetMachine(
   // LLVM 'unreachable' to ISD::TRAP and then lower that to WebAssembly's
   // 'unreachable' instructions which is meant for that case.
   this->Options.TrapUnreachable = true;
+  this->Options.NoTrapAfterNoreturn = false;
 
   // WebAssembly treats each function as an independent unit. Force
   // -ffunction-sections, effectively, so that we can emit them independently.

llvm/test/CodeGen/WebAssembly/unreachable.ll

@@ -1,33 +1,97 @@
-; RUN: llc < %s -asm-verbose=false -verify-machineinstrs | FileCheck %s
-; RUN: llc < %s -asm-verbose=false -fast-isel -fast-isel-abort=1 -verify-machineinstrs | FileCheck %s
+; The assertions in this file were autogenerated by
+; utils/update_llc_test_checks.py, but were hand-edited to add the
+; "end_function" lines to prevent the tests from passing when there are
+; superfluous instructions at the end of a function. You can run
+; update_llc_test_checks.py again, but please keep the "end_function" lines
+; intact when you commit.
 
-; Test that LLVM unreachable instruction and trap intrinsic are lowered to
-; wasm unreachable
+; Wasm, to generate valid code, always internally sets `--trap-unreachable` to 1
+; and `--no-trap-after-noreturn` to 0, and these command lines options, if
+; explicitly given, are ignored. Various combinations of these options should
+; have no effect and should not generate invalid code.
+; RUN: llc < %s -verify-machineinstrs | FileCheck %s
+; RUN: llc < %s -fast-isel -fast-isel-abort=1 -verify-machineinstrs | FileCheck %s
+; RUN: llc < %s -verify-machineinstrs --trap-unreachable | FileCheck %s
+; RUN: llc < %s -fast-isel -fast-isel-abort=1 -verify-machineinstrs --trap-unreachable | FileCheck %s
+; RUN: llc < %s -verify-machineinstrs --trap-unreachable --no-trap-after-noreturn | FileCheck %s
+; RUN: llc < %s -fast-isel -fast-isel-abort=1 -verify-machineinstrs --trap-unreachable --no-trap-after-noreturn | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
 
-declare void @llvm.trap()
-declare void @llvm.debugtrap()
-declare void @abort()
 
-; CHECK-LABEL: f1:
-; CHECK: call abort{{$}}
-; CHECK: unreachable
-define i32 @f1() {
-  call void @abort()
-  unreachable
-}
+; Test that the LLVM trap and debug trap intrinsics are lowered to wasm
+; unreachable.
 
-; CHECK-LABEL: f2:
-; CHECK: unreachable
-define void @f2() {
+declare void @llvm.trap() cold noreturn nounwind
+declare void @llvm.debugtrap() nounwind
+
+define void @trap_ret_void() {
+; CHECK-LABEL: trap_ret_void:
+; CHECK:         .functype trap_ret_void () -> ()
+; CHECK-NEXT:  # %bb.0:
+; CHECK-NEXT:    unreachable
+; CHECK-NEXT:    # fallthrough-return
+; CHECK-NEXT:    end_function
   call void @llvm.trap()
   ret void
 }
 
-; CHECK-LABEL: f3:
-; CHECK: unreachable
-define void @f3() {
+define void @debugtrap_ret_void() {
+; CHECK-LABEL: debugtrap_ret_void:
+; CHECK:         .functype debugtrap_ret_void () -> ()
+; CHECK-NEXT:  # %bb.0:
+; CHECK-NEXT:    unreachable
+; CHECK-NEXT:    # fallthrough-return
+; CHECK-NEXT:    end_function
   call void @llvm.debugtrap()
   ret void
 }
+
+; LLVM trap followed by LLVM unreachable could become exactly one wasm
+; unreachable, but two are emitted currently.
+define void @trap_unreacheable() {
+; CHECK-LABEL: trap_unreacheable:
+; CHECK:         .functype trap_unreacheable () -> ()
+; CHECK-NEXT:  # %bb.0:
+; CHECK-NEXT:    unreachable
+; CHECK-NEXT:    unreachable
+; CHECK-NEXT:    end_function
+  call void @llvm.trap()
+  unreachable
+}
+
+
+; Test that LLVM unreachable instruction is lowered to wasm unreachable when
+; necessary to fulfill the wasm operand stack requirements.
+
+declare void @ext_func()
+declare i32 @ext_func_i32()
+declare void @ext_never_return() noreturn
+
+; LLVM IR's 'unreachable' is translated to Wasm 'unreachable'.
+define i32 @missing_ret_unreachable() {
+; CHECK-LABEL: missing_ret_unreachable:
+; CHECK:         .functype missing_ret_unreachable () -> (i32)
+; CHECK-NEXT:  # %bb.0:
+; CHECK-NEXT:    call ext_func
+; CHECK-NEXT:    unreachable
+; CHECK-NEXT:    end_function
+  call void @ext_func()
+  unreachable
+}
+
+; This is similar to the above test, but ensures wasm unreachable is emitted
+; This is similar to the above test, but the callee has a 'noreturn' attribute.    
+; There is an optimization that removes an 'unreachable' after a noreturn call,  
+; but Wasm backend doesn't use it and ignore `--no-trap-after-noreturn`, if      
+; given, to generate valid code. 
+define i32 @missing_ret_noreturn_unreachable() {
+; CHECK-LABEL: missing_ret_noreturn_unreachable:
+; CHECK:         .functype missing_ret_noreturn_unreachable () -> (i32)
+; CHECK-NEXT:  # %bb.0:
+; CHECK-NEXT:    call ext_never_return
+; CHECK-NEXT:    unreachable
+; CHECK-NEXT:    end_function
+  call void @ext_never_return()
+  unreachable
+}