SimplifyCFG: Don't generate invalid code for switch used to initialize

two variables where the first variable is returned and the second
ignored.

I don't think this occurs in practice (other passes should have cleaned
up the unused phi node), but it should still be handled correctly.

Also make the logic for determining if we should return early less
sketchy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164225 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 42 insertions, 9 deletions

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 3365c2feed..7c6a152329 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3258,17 +3258,16 @@ static bool SwitchToLookupTable(SwitchInst *SI,
                                            "switch.gep");
     Value *Result = Builder.CreateLoad(GEP, "switch.load");
 
-    // If the result is only going to be used to return from the function,
-    // we want to do that right here.
-    if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->use_begin())) {
-      if (CommonDest->getFirstNonPHIOrDbg() == CommonDest->getTerminator()) {
-        Builder.CreateRet(Result);
-        ReturnedEarly = true;
-      }
+    // If the result is used to return immediately from the function, we want to
+    // do that right here.
+    if (PHI->hasOneUse() && isa<ReturnInst>(*PHI->use_begin()) &&
+        *PHI->use_begin() == CommonDest->getFirstNonPHIOrDbg()) {
+      Builder.CreateRet(Result);
+      ReturnedEarly = true;
+      break;
     }
 
-    if (!ReturnedEarly)
-      PHI->addIncoming(Result, LookupBB);
+    PHI->addIncoming(Result, LookupBB);
   }
 
   if (!ReturnedEarly)
diff --git a/test/Transforms/SimplifyCFG/switch_to_lookup_table.ll b/test/Transforms/SimplifyCFG/switch_to_lookup_table.ll
index 414da93976..f0bd688050 100644
--- a/test/Transforms/SimplifyCFG/switch_to_lookup_table.ll
+++ b/test/Transforms/SimplifyCFG/switch_to_lookup_table.ll
@@ -15,6 +15,9 @@ target triple = "x86_64-unknown-linux-gnu"
 ; The table for @foostring
 ; CHECK: @switch.table3 = private unnamed_addr constant [4 x i8*] [i8* getelementptr inbounds ([4 x i8]* @.str, i64 0, i64 0), i8* getelementptr inbounds ([4 x i8]* @.str1, i64 0, i64 0), i8* getelementptr inbounds ([4 x i8]* @.str2, i64 0, i64 0), i8* getelementptr inbounds ([4 x i8]* @.str3, i64 0, i64 0)]
 
+; The table for @earlyreturncrash
+; CHECK: @switch.table4 = private unnamed_addr constant [4 x i32] [i32 42, i32 9, i32 88, i32 5]
+
 ; A simple int-to-int selection switch.
 ; It is dense enough to be replaced by table lookup.
 ; The result is directly by a ret from an otherwise empty bb,
@@ -138,3 +141,34 @@ return:
 ; CHECK-NEXT: %switch.load = load i8** %switch.gep
 ; CHECK-NEXT: ret i8* %switch.load
 }
+
+; Switch used to initialize two values. The first value is returned, the second
+; value is not used. This used to make the transformation generate illegal code.
+
+define i32 @earlyreturncrash(i32 %x)  {
+entry:
+  switch i32 %x, label %sw.default [
+    i32 0, label %sw.epilog
+    i32 1, label %sw.bb1
+    i32 2, label %sw.bb2
+    i32 3, label %sw.bb3
+  ]
+
+sw.bb1: br label %sw.epilog
+sw.bb2: br label %sw.epilog
+sw.bb3: br label %sw.epilog
+sw.default: br label %sw.epilog
+
+sw.epilog:
+  %a.0 = phi i32 [ 7, %sw.default ], [ 5, %sw.bb3 ], [ 88, %sw.bb2 ], [ 9, %sw.bb1 ], [ 42, %entry ]
+  %b.0 = phi i32 [ 10, %sw.default ], [ 5, %sw.bb3 ], [ 1, %sw.bb2 ], [ 4, %sw.bb1 ], [ 3, %entry ]
+  ret i32 %a.0
+
+; CHECK: @earlyreturncrash
+; CHECK: switch.lookup:
+; CHECK-NEXT: %switch.gep = getelementptr inbounds [4 x i32]* @switch.table4, i32 0, i32 %switch.tableidx
+; CHECK-NEXT: %switch.load = load i32* %switch.gep
+; CHECK-NEXT: ret i32 %switch.load
+; CHECK: sw.epilog:
+; CHECK-NEXT: ret i32 7
+}