SimplifyCFG: don't remove unreachable default switch destinations

An unreachable default destination can be exploited by other optimizations and
allows for more efficient lowering. Both the SDag switch lowering and
LowerSwitch can exploit unreachable defaults.

Also make TurnSwitchRangeICmp handle switches with unreachable default.
This is kind of separate change, but it cannot be tested without the change
above, and I don't want to land the change above without this since that would
regress other tests.

Differential Revision: http://reviews.llvm.org/D6471

llvm-svn: 227125

4 files changed, 34 insertions, 68 deletions

diff --git a/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll b/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
index 21428c62f53..22b144b5cb8 100644
--- a/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
+++ b/llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
@@ -46,32 +46,6 @@ T:
         ret i32 2
 }
 
-; PR9450
-define i32 @test4(i32 %v, i32 %w) {
-; CHECK: entry:
-; CHECK-NEXT:  switch i32 %v, label %T [
-; CHECK-NEXT:    i32 3, label %V
-; CHECK-NEXT:    i32 2, label %U
-; CHECK-NEXT:  ]
-
-entry:
-        br label %SWITCH
-V:
-        ret i32 7
-SWITCH:
-        switch i32 %v, label %default [
-                 i32 1, label %T
-                 i32 2, label %U
-                 i32 3, label %V
-        ]
-default:
-        unreachable
-U:
-        ret i32 %w
-T:
-        ret i32 2
-}
-
 
 ;; We can either convert the following control-flow to a select or remove the
 ;; unreachable control flow because of the undef store of null. Make sure we do
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 22f18cd4d43..9cf57b38dfe 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -21,8 +21,8 @@ target triple = "x86_64-unknown-linux-gnu"
 ; The table for @cprop
 ; CHECK: @switch.table5 = private unnamed_addr constant [7 x i32] [i32 5, i32 42, i32 126, i32 -452, i32 128, i32 6, i32 7]
 
-; The table for @unreachable
-; CHECK: @switch.table6 = private unnamed_addr constant [5 x i32] [i32 0, i32 0, i32 0, i32 1, i32 -1]
+; The table for @unreachable_case
+; CHECK: @switch.table6 = private unnamed_addr constant [9 x i32] [i32 0, i32 0, i32 0, i32 2, i32 -1, i32 1, i32 1, i32 1, i32 1]
 
 ; A simple int-to-int selection switch.
 ; It is dense enough to be replaced by table lookup.
@@ -752,7 +752,7 @@ return:
 ; CHECK: %switch.gep = getelementptr inbounds [7 x i32]* @switch.table5, i32 0, i32 %switch.tableidx
 }
 
-define i32 @unreachable(i32 %x)  {
+define i32 @unreachable_case(i32 %x)  {
 entry:
   switch i32 %x, label %sw.default [
     i32 0, label %sw.bb
@@ -770,15 +770,15 @@ sw.bb: br label %return
 sw.bb1: unreachable
 sw.bb2: br label %return
 sw.bb3: br label %return
-sw.default: unreachable
+sw.default: br label %return
 
 return:
-  %retval.0 = phi i32 [ 1, %sw.bb3 ], [ -1, %sw.bb2 ], [ 0, %sw.bb ]
+  %retval.0 = phi i32 [ 1, %sw.bb3 ], [ -1, %sw.bb2 ], [ 0, %sw.bb ], [ 2, %sw.default ]
   ret i32 %retval.0
 
-; CHECK-LABEL: @unreachable(
+; CHECK-LABEL: @unreachable_case(
 ; CHECK: switch.lookup:
-; CHECK: getelementptr inbounds [5 x i32]* @switch.table6, i32 0, i32 %switch.tableidx
+; CHECK: getelementptr inbounds [9 x i32]* @switch.table6, i32 0, i32 %switch.tableidx
 }
 
 ; Don't create a table with illegal type
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-range-to-icmp.ll b/llvm/test/Transforms/SimplifyCFG/switch-range-to-icmp.ll
index 8bf2b04520b..a109b317c73 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch-range-to-icmp.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch-range-to-icmp.ll
@@ -48,3 +48,30 @@ b:
   %1 = call i32 @f(i32 1)
   ret i32 %1
 }
+
+
+define i32 @unreachable2(i32 %x) {
+; CHECK-LABEL: @unreachable2
+; CHECK: x.off = add i32 %x, -5
+; CHECK: %switch = icmp ult i32 %x.off, 3
+; CHECK: br i1 %switch, label %a, label %b
+
+entry:
+  ; Note: folding the most popular case destination into the default
+  ; would prevent switch-to-icmp here.
+  switch i32 %x, label %unreachable [
+    i32 5, label %a
+    i32 6, label %a
+    i32 7, label %a
+    i32 10, label %b
+    i32 20, label %b
+  ]
+unreachable:
+  unreachable
+a:
+  %0 = call i32 @f(i32 0)
+  ret i32 %0
+b:
+  %1 = call i32 @f(i32 1)
+  ret i32 %1
+}
diff --git a/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll b/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll
index 69f97e5f9f9..f4d171ad2b1 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch-to-select-two-case.ll
@@ -35,38 +35,3 @@ return:
   %retval.0 = phi i32 [ 4, %sw.epilog ], [ 2, %sw.bb1 ], [ 10, %sw.bb ]
   ret i32 %retval.0
 }
-
-; int foo1_without_default(int a) {
-;   switch(a) {
-;     case 10:
-;       return 10;
-;     case 20:
-;       return 2;
-;   }
-;   __builtin_unreachable();
-; }
-
-define i32 @foo1_without_default(i32 %a) {
-; CHECK-LABEL: @foo1_without_default
-; CHECK: %switch.selectcmp = icmp eq i32 %a, 10
-; CHECK-NEXT: %switch.select = select i1 %switch.selectcmp, i32 10, i32 2
-; CHECK-NOT: %switch.selectcmp1
-entry:
-  switch i32 %a, label %sw.epilog [
-    i32 10, label %sw.bb
-    i32 20, label %sw.bb1
-  ]
-
-sw.bb:
-  br label %return
-
-sw.bb1:
-  br label %return
-
-sw.epilog:
-  unreachable
-
-return:
-  %retval.0 = phi i32 [ 2, %sw.bb1 ], [ 10, %sw.bb ]
-  ret i32 %retval.0
-}