From: Hans Wennborg <hans@hanshq.net>
Date: Tue, 16 Apr 2013 08:35:36 +0000 (+0000)
Subject: simplifycfg: Fix integer overflow converting switch into icmp.
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=a121e24c541097b51309a06297005ac257b6728f;p=oota-llvm.git

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
---

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
+}