SimplifyCFG: Correctly handle switch lookup tables which fully cover the input type and use bit tests to check for holes

When using bit tests for hole checks, we call AddPredecessorToBlock to give the
phi node a value from the bit test block. This would break if we've
previously called removePredecessor on the default destination because the
switch is fully covered.

Test case by Mark Lacey.

llvm-svn: 235771

1 files changed, 29 insertions, 0 deletions

diff --git a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
index cdc0488991a..732e7cafe5e 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -1273,3 +1273,32 @@ end:
 ; CHECK-LABEL: @pr20210
 ; CHECK: switch i8 %x
 }
+
+; Make sure we do not crash due to trying to generate an unguarded
+; lookup (since i3 can only hold values in the range of explicit
+; values) and simultaneously trying to generate a branch to deal with
+; the fact that we have holes in the range.
+define i32 @covered_switch_with_bit_tests(i3) {
+entry:
+  switch i3 %0, label %l6 [
+    i3 -3, label %l5
+    i3 -4, label %l5
+    i3 3, label %l1
+    i3 2, label %l1
+  ]
+
+l1: br label %l2
+
+l2:
+  %x = phi i32 [ 1, %l1 ], [ 2, %l5 ]
+  br label %l6
+
+l5: br label %l2
+
+l6:
+  %r = phi i32 [ %x, %l2 ], [ 0, %entry ]
+  ret i32 %r
+; CHECK-LABEL: @covered_switch_with_bit_tests
+; CHECK: entry
+; CHECK-NEXT: switch
+}