[IROutliner] handle functions that do not contain an exit path

[AndrewLitteken]

Summary

As a result of adding multiblock outlining, it became possible to outline the entirety of basic block, and branches that only pointed to the basic blocks contained in the outlined section. This means that there are no exit paths, and no return statement. There was a previous assertion from the older version of the outliner that explicitly made sure there was a return statement. This removes that assertion.

It does not break any of the tests for the outliner. I will test it on the test suite to make sure.

[paquette]

LGTM

I am a little worried about the code extractor's assumptions, at least wrt noreturn functions (should the code extractor have a special case for noreturn?). But I think that should be handled in the code extractor, not here.

llvm/lib/Transforms/IPO/IROutliner.cpp

for (Instruction &Val : CurrBB) {
         DILocation *DI = DILocation::get(New.getContext(), 0, 0, SP);
         Val.setDebugLoc(DI);
       }
     }
 
     for (Instruction *I : DebugInsts)
       I->eraseFromParent();
   }
-
-  assert(NewEnds.size() > 0 && "No return instruction for new function?");
 }
 
 /// Find the the constants that will need to be lifted into arguments
 /// as they are not the same in each instance of the region.
 ///
 /// \param [in] C - The IRSimilarityCandidate containing the region we are
 /// analyzing.
 /// \param [in] NotSame - The set of global value numbers that do not have a

llvm/test/Transforms/IROutliner/outlining-no-return-functions.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --include-generated-funcs
+; RUN: opt -S -verify -iroutliner -ir-outlining-no-cost < %s | FileCheck %s
+
+; Make sure that we outline safely from functions with no return instructions.
+
+; The code extractor will insert return instructions in the outer function
+; due to assumptions about the contents of the outlined region.
+
+define void @f1() {
+bb:
+  br label %bb1
+bb1:
+  br label %bb1
+}
+
+define void @f2() {
+bb:
+  br label %bb1
+bb1:
+  br label %bb1
+}
+
+define void @f3() {
+bb:
+  br label %bb1
+bb1:
+  br label %bb1
+}
+; CHECK-LABEL: @f1(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    br label [[BB1:%.*]]
+; CHECK:       bb1:
+; CHECK-NEXT:    br label [[BB1]]
+;
+;
+; CHECK-LABEL: @f2(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    call void @outlined_ir_func_0()
+; CHECK-NEXT:    ret void
+;
+;
+; CHECK-LABEL: @f3(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    call void @outlined_ir_func_0()
+; CHECK-NEXT:    ret void
+;
+;
+; CHECK-LABEL: define internal void @outlined_ir_func_0(
+; CHECK-NEXT:  newFuncRoot:
+; CHECK-NEXT:    br label [[BB_TO_OUTLINE:%.*]]
+; CHECK:       bb_to_outline:
+; CHECK-NEXT:    br label [[BB1:%.*]]
+; CHECK:       bb1:
+; CHECK-NEXT:    br label [[BB1]]
+;