From a121e24c541097b51309a06297005ac257b6728f Mon Sep 17 00:00:00 2001
From: Hans Wennborg <hans@hanshq.net>
Date: Tue, 16 Apr 2013 08:35:36 +0000
Subject: [PATCH] simplifycfg: Fix integer overflow converting switch into
 icmp.

If a switch instruction has a case for every possible value of its type,
with the same successor, SimplifyCFG would replace it with an icmp ult,
but the computation of the bound overflows in that case, which inverts
the test.

Patch by Jed Davis!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179587 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/SimplifyCFG.cpp          |  7 ++++++-
 test/Transforms/SimplifyCFG/switch-to-icmp.ll | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 681bf9c2b7a..6de602e4c3e 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3073,7 +3073,12 @@ static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
   Value *Sub = SI->getCondition();
   if (!Offset->isNullValue())
     Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
-  Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
+  Value *Cmp;
+  // If NumCases overflowed, then all possible values jump to the successor.
+  if (NumCases->isNullValue() && SI->getNumCases() != 0)
+    Cmp = ConstantInt::getTrue(SI->getContext());
+  else
+    Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
   BranchInst *NewBI = Builder.CreateCondBr(
       Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
 
diff --git a/test/Transforms/SimplifyCFG/switch-to-icmp.ll b/test/Transforms/SimplifyCFG/switch-to-icmp.ll
index 414f8475bc2..e9a6db45cb0 100644
--- a/test/Transforms/SimplifyCFG/switch-to-icmp.ll
+++ b/test/Transforms/SimplifyCFG/switch-to-icmp.ll
@@ -37,3 +37,21 @@ lor.end:
 ; CHECK: @test2
 ; CHECK: %switch = icmp ult i32 %x, 2
 }
+
+define i32 @test3(i1 %flag) {
+entry:
+ switch i1 %flag, label %bad [
+   i1 true, label %good
+   i1 false, label %good
+ ]
+
+good:
+ ret i32 0
+
+bad:
+ ret i32 1
+
+; CHECK: @test3
+; CHECK: entry:
+; CHECK-NEXT: ret i32 0
+}
-- 
2.34.1