[Attributor][Fix] Make sure we do not delete live code

[jdoerfert]

Summary

Liveness needs to mark edges, not blocks as dead.

[sstefan1]

LGTM

llvm/lib/Transforms/IPO/Attributor.cpp

for (const Instruction *NRC : NoReturnCalls) {
               CI->insertBefore(II);
               CI->takeName(II);
               II->replaceAllUsesWith(CI);
               SplitPos = CI->getNextNode();
             }
           }
         }
 
-        if (SplitPos == &NormalDestBB->front())
-          assumeLive(A, *NormalDestBB);
+        if (SplitPos == &NormalDestBB->front()) {
+          // If this is an invoke of a noreturn function the edge to the normal
+          // destination block is dead but not necessarily the block itself.
+          // TODO: We need to move to an edge based system during deduction and
+          //       also manifest.
+          assert(!NormalDestBB->isLandingPad() &&
+                 "Expected the normal destination not to be a landingpad!");
+          BasicBlock *SplitBB =
+              SplitBlockPredecessors(NormalDestBB, {BB}, ".dead");
+          // The split block is live even if it contains only an unreachable
+          // instruction at the end.
+          assumeLive(A, *SplitBB);
+          SplitPos = SplitBB->getTerminator();
+        }
       }
 
       BB = SplitPos->getParent();
       SplitBlock(BB, SplitPos);
       changeToUnreachable(BB->getTerminator(), /* UseLLVMTrap */ false);
       HasChanged = ChangeStatus::CHANGED;
     }
 

llvm/test/Transforms/FunctionAttrs/liveness.ll

entry:
   %cmp = icmp eq i32 %a, 0
   br i1 %cmp, label %cond.true, label %cond.false
 
 cond.true:                                        ; preds = %entry
   call void @normal_call()
   %call = invoke i32 @foo_noreturn() to label %continue
             unwind label %cleanup
   ; CHECK:      %call = invoke i32 @foo_noreturn()
-  ; CHECK-NEXT:         to label %continue unwind label %cleanup
+  ; CHECK-NEXT:         to label %continue.dead unwind label %cleanup
 
 cond.false:                                       ; preds = %entry
   call void @normal_call()
   %call1 = call i32 @bar()
   br label %cond.end
 
 cond.end:                                         ; preds = %cond.false, %continue
   %cond = phi i32 [ %call, %continue ], [ %call1, %cond.false ]
   ret i32 %cond
 
 continue:
-  ; CHECK:      continue:
+  ; CHECK:      continue.dead:
   ; CHECK-NEXT: unreachable
   br label %cond.end
 
 cleanup:
   %res = landingpad { i8*, i32 }
   catch i8* null
   ret i32 0
 }

 ; CHECK: define internal void @non_dead_d11()
 ; CHECK: define internal void @non_dead_d12()
 ; CHECK: define internal void @non_dead_d13()
 ; CHECK: define internal void @non_dead_d14()
 ; Verify we actually deduce information for these functions.
 ; CHECK: Function Attrs: nofree nosync nounwind willreturn
 ; CHECK-NEXT: define internal void @non_dead_d15()
 ; CHECK-NOT: define internal void @dead_e
+
+
+declare void @blowup() noreturn
+define void @live_with_dead_entry() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+; CHECK:      define void @live_with_dead_entry(
+; CHECK-NEXT: entry:
+; CHECK-NEXT:   invoke void @blowup()
+; CHECK-NEXT:           to label %live_with_dead_entry.dead unwind label %lpad
+; CHECK:      lpad:                                             ; preds = %entry
+; CHECK-NEXT:   %0 = landingpad { i8*, i32 }
+; CHECK-NEXT:           catch i8* null
+; CHECK-NEXT:   br label %live_with_dead_entry
+; CHECK:      live_with_dead_entry.dead:                        ; preds = %entry
+; CHECK-NEXT:   unreachable
+; CHECK:      live_with_dead_entry:                             ; preds = %lpad
+; CHECK-NEXT:   ret void
+entry:
+  invoke void @blowup() to label %live_with_dead_entry unwind label %lpad
+lpad:
+  %0 = landingpad { i8*, i32 } catch i8* null
+  br label %live_with_dead_entry
+live_with_dead_entry:
+  ret void
+}
+
+define void @live_with_dead_entry_lp() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+; CHECK:      define void @live_with_dead_entry_lp(
+; CHECK-NEXT: entry:
+; CHECK-NEXT:   invoke void @blowup()
+; CHECK-NEXT:           to label %live_with_dead_entry.dead unwind label %lp1
+; CHECK:      lp1:                                              ; preds = %entry
+; CHECK-NEXT:   %lp = landingpad { i8*, i32 }
+; CHECK-NEXT:           catch i8* null
+; CHECK-NEXT:   invoke void @blowup()
+; CHECK-NEXT:           to label %live_with_dead_entry.dead1 unwind label %lp2
+; CHECK:      lp2:                                              ; preds = %lp1
+; CHECK-NEXT:   %0 = landingpad { i8*, i32 }
+; CHECK-NEXT:           catch i8* null
+; CHECK-NEXT:   br label %live_with_dead_entry
+; CHECK:      live_with_dead_entry.dead:                        ; preds = %entry
+; CHECK-NEXT:   unreachable
+; CHECK:      live_with_dead_entry.dead1:                       ; preds = %lp1
+; CHECK-NEXT:   unreachable
+; CHECK:      live_with_dead_entry:                             ; preds = %lp2
+; CHECK-NEXT:   ret void
+entry:
+  invoke void @blowup() to label %live_with_dead_entry unwind label %lp1
+lp1:
+  %lp = landingpad { i8*, i32 } catch i8* null
+  invoke void @blowup() to label %live_with_dead_entry unwind label %lp2
+lp2:
+  %0 = landingpad { i8*, i32 } catch i8* null
+  br label %live_with_dead_entry
+live_with_dead_entry:
+  ret void
+}

llvm/test/Transforms/FunctionAttrs/noreturn_async.ll

 ; CHECK-NOT:    noreturn
 ; CHECK:        define
 ; CHECK-SAME:   @"?catchoverflow@@YAHXZ"()
 define dso_local i32 @"?catchoverflow@@YAHXZ"()  personality i8* bitcast (i32 (...)* @__C_specific_handler to i8*) {
 entry:
   %retval = alloca i32, align 4
   %__exception_code = alloca i32, align 4
 ; CHECK: invoke void @"?overflow@@YAXXZ"()
-; CHECK:          to label %invoke.cont unwind label %catch.dispatch
+; CHECK:          to label %invoke.cont.dead unwind label %catch.dispatch
   invoke void @"?overflow@@YAXXZ"()
           to label %invoke.cont unwind label %catch.dispatch
 
 invoke.cont:                                      ; preds = %entry
-; CHECK:      invoke.cont:
+; CHECK:      invoke.cont.dead:
 ; CHECK-NEXT: unreachable
   br label %invoke.cont1
 
 catch.dispatch:                                   ; preds = %invoke.cont, %entry
   %0 = catchswitch within none [label %__except] unwind to caller
 
 __except:                                         ; preds = %catch.dispatch
   %1 = catchpad within %0 [i8* null]

 ; CHECK-NOT:    noreturn
 ; CHECK:        define
 ; CHECK-SAME:   @"?catchoverflow@@YAHXZ_may_throw"()
 define dso_local i32 @"?catchoverflow@@YAHXZ_may_throw"()  personality i8* bitcast (i32 (...)* @__C_specific_handler to i8*) {
 entry:
   %retval = alloca i32, align 4
   %__exception_code = alloca i32, align 4
 ; CHECK: invoke void @"?overflow@@YAXXZ_may_throw"() 
-; CHECK:          to label %invoke.cont unwind label %catch.dispatch
+; CHECK:          to label %invoke.cont.dead unwind label %catch.dispatch
   invoke void @"?overflow@@YAXXZ_may_throw"() 
           to label %invoke.cont unwind label %catch.dispatch
 
 invoke.cont:                                      ; preds = %entry
-; CHECK:      invoke.cont:
+; CHECK:      invoke.cont.dead:
 ; CHECK-NEXT: unreachable
   br label %invoke.cont1
 
 catch.dispatch:                                   ; preds = %invoke.cont, %entry
   %0 = catchswitch within none [label %__except] unwind to caller
 
 __except:                                         ; preds = %catch.dispatch
   %1 = catchpad within %0 [i8* null]

llvm/test/Transforms/FunctionAttrs/noreturn_sync.ll

 ; CHECK-NOT:    noreturn
 ; CHECK:        define
 ; CHECK-SAME:   @"?catchoverflow@@YAHXZ_may_throw"()
 define dso_local i32 @"?catchoverflow@@YAHXZ_may_throw"()  personality i8* bitcast (i32 (...)* @__gcc_personality_v0 to i8*) {
 entry:
   %retval = alloca i32, align 4
   %__exception_code = alloca i32, align 4
 ; CHECK: invoke void @"?overflow@@YAXXZ_may_throw"() 
-; CHECK:          to label %invoke.cont unwind label %catch.dispatch
+; CHECK:          to label %invoke.cont.dead unwind label %catch.dispatch
   invoke void @"?overflow@@YAXXZ_may_throw"() 
           to label %invoke.cont unwind label %catch.dispatch
 
 invoke.cont:                                      ; preds = %entry
-; CHECK:      invoke.cont:
+; CHECK:      invoke.cont.dead:
 ; CHECK-NEXT: unreachable
   br label %invoke.cont1
 
 catch.dispatch:                                   ; preds = %invoke.cont, %entry
   %0 = catchswitch within none [label %__except] unwind to caller
 
 __except:                                         ; preds = %catch.dispatch
   %1 = catchpad within %0 [i8* null]