From c471bb2e673a916e5daa5ba643eabbd30a20fc4a Mon Sep 17 00:00:00 2001
From: Ayonam Ray <ayonam@rrlogic.co.in>
Date: Tue, 1 Jan 2019 06:37:50 +0000
Subject: Omit range checks from jump tables when lowering switches with
 unreachable default

During the lowering of a switch that would result in the generation of a jump
table, a range check is performed before indexing into the jump table, for the
switch value being outside the jump table range and a conditional branch is
inserted to jump to the default block. In case the default block is
unreachable, this conditional jump can be omitted. This patch implements
omitting this conditional branch for unreachable defaults.

Review Reference: D52002

llvm-svn: 350186
---
 .../CodeGen/AArch64/switch-unreachable-default.ll  | 62 ++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 llvm/test/CodeGen/AArch64/switch-unreachable-default.ll

(limited to 'llvm/test/CodeGen/AArch64/switch-unreachable-default.ll')

diff --git a/llvm/test/CodeGen/AArch64/switch-unreachable-default.ll b/llvm/test/CodeGen/AArch64/switch-unreachable-default.ll
new file mode 100644
index 00000000000..7ddcd51cc02
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/switch-unreachable-default.ll
@@ -0,0 +1,62 @@
+; RUN: llc -O3 -o - %s | FileCheck %s
+
+; Test that the output in the presence of an unreachable default does not have
+; a compare and branch at the top of the switch to handle the default case.
+
+target triple = "aarch64-unknown-linux-gnu"
+
+; Function Attrs: nounwind
+define void @fn(i4) {
+  switch i4 %0, label %default [
+    i4 0, label %case_0
+    i4 1, label %case_1
+    i4 2, label %case_2
+    i4 3, label %case_3
+    i4 4, label %case_4
+    i4 5, label %case_5
+  ]
+
+; CHECK-LABEL: fn:
+; CHECK-NOT:    sub
+; CHECK-NOT:    cmp
+; CHECK-NOT:    b.hi
+; CHECK:        ldr {{x[0-9]+}}, [{{x[0-9]+}}, {{x[0-9]+}}, lsl #3]
+; CHECK:        br {{x[0-9]+}}
+
+default:
+  unreachable
+
+case_0:
+  tail call void @handle_case_00(i4 %0) #2
+  br label %return_label
+
+case_1:
+  tail call void @handle_case_01(i4 %0) #2
+  br label %return_label
+
+case_2:
+  tail call void @handle_case_02(i4 %0) #2
+  br label %return_label
+
+case_3:
+  tail call void @handle_case_03(i4 %0) #2
+  br label %return_label
+
+case_4:
+  tail call void @handle_case_04(i4 %0) #2
+  br label %return_label
+
+case_5:
+  tail call void @handle_case_05(i4 %0) #2
+  br label %return_label
+
+return_label:
+  ret void
+}
+
+declare  void @handle_case_00(i4)
+declare  void @handle_case_01(i4)
+declare  void @handle_case_02(i4)
+declare  void @handle_case_03(i4)
+declare  void @handle_case_04(i4)
+declare  void @handle_case_05(i4)
-- 
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