[LoopSimplifyCFG] Add test case for PR54023.

Test case for #54023.

llvm/test/Transforms/LoopSimplifyCFG/loop-not-in-simplify-form.ll

@@ -0,0 +1,57 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes='loop-mssa(loop-instsimplify,loop-simplifycfg,simple-loop-unswitch)' -S %s | FileCheck %s
+
+; Test case from PR54023. After SimpleLoopUnswitch, one of the loops processed
+; by LoopSimplifyCFG will have exit blocks with predecessors outside the loop
+; (i.e. it is not in loop-simplify/canonical form).
+; FIXME: currently %res gets incorrectly replaced with undef.
+define i32 @test(i32 %v, i1 %c.1, i1 %c.2) {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    switch i32 0, label [[ENTRY_SPLIT:%.*]] [
+; CHECK-NEXT:    i32 1, label [[EXIT_SPLIT:%.*]]
+; CHECK-NEXT:    ]
+; CHECK:       entry.split:
+; CHECK-NEXT:    br label [[OUTER_HEADER:%.*]]
+; CHECK:       outer.header:
+; CHECK-NEXT:    br i1 [[C_1:%.*]], label [[OUTER_LATCH:%.*]], label [[INNER_HEADER_PREHEADER:%.*]]
+; CHECK:       inner.header.preheader:
+; CHECK-NEXT:    br label [[INNER_HEADER:%.*]]
+; CHECK:       inner.header:
+; CHECK-NEXT:    [[CMP_2:%.*]] = icmp ne i32 [[V:%.*]], 0
+; CHECK-NEXT:    br i1 [[CMP_2]], label [[EXIT:%.*]], label [[INNER_LATCH:%.*]]
+; CHECK:       inner.latch:
+; CHECK-NEXT:    br i1 [[C_2:%.*]], label [[OUTER_LATCH_LOOPEXIT:%.*]], label [[INNER_HEADER]]
+; CHECK:       outer.latch.loopexit:
+; CHECK-NEXT:    br label [[OUTER_LATCH]]
+; CHECK:       outer.latch:
+; CHECK-NEXT:    br label [[OUTER_HEADER]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[RES:%.*]] = phi i32 [ [[V]], [[INNER_HEADER]] ]
+; CHECK-NEXT:    br label [[EXIT_SPLIT]]
+; CHECK:       exit.split:
+; CHECK-NEXT:    ret i32 undef
+;
+entry:
+  br label %outer.header
+
+outer.header:
+  %g.0 = phi i32 [ 10, %outer.latch ], [ 1, %entry ]
+  %cmp.1 = icmp eq i32 %g.0, 0
+  br i1 %c.1, label %outer.latch, label %inner.header
+
+inner.header:
+  %cmp.2 = icmp ne i32 %v, 0
+  %or.cond = or i1 %cmp.1, %cmp.2
+  br i1 %or.cond, label %exit, label %inner.latch
+
+inner.latch:
+  br i1 %c.2, label %outer.latch, label %inner.header
+
+outer.latch:
+  br label %outer.header
+
+exit:
+  %res = phi i32 [ %v, %inner.header ]
+  ret i32 %res
+}