From 042b27f40e4b1dcae70c0e98c3b4f5760dd8fa9b Mon Sep 17 00:00:00 2001
From: Benjamin Kramer <benny.kra@googlemail.com>
Date: Thu, 3 Feb 2011 22:51:41 +0000
Subject: [PATCH] SimplifyCFG: Also transform switches that represent a range
 comparison but are not sorted into sub+icmp.

This transforms another 1000 switches in gcc.c.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124826 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/SimplifyCFG.cpp          | 25 ++++++++----
 test/Transforms/SimplifyCFG/switch-to-icmp.ll | 40 +++++++++++++++++++
 2 files changed, 58 insertions(+), 7 deletions(-)
 create mode 100644 test/Transforms/SimplifyCFG/switch-to-icmp.ll

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index bf753dc05d4..93d81435760 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2241,14 +2241,25 @@ bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
 /// integer range comparison into a sub, an icmp and a branch.
 static bool TurnSwitchRangeIntoICmp(SwitchInst *SI) {
   assert(SI->getNumCases() > 2 && "Degenerate switch?");
-  // We can do this transform if the switch consists of an ascending series
-  // and all cases point to the same destination.
-  for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I)
-    if (SI->getSuccessor(I-1) != SI->getSuccessor(I) ||
-        SI->getCaseValue(I-1)->getValue()+1 != SI->getCaseValue(I)->getValue())
-      return false;
 
-  Constant *Offset = ConstantExpr::getNeg(SI->getCaseValue(1));
+  // Make sure all cases point to the same destination and gather the values.
+  SmallVector<ConstantInt *, 16> Cases;
+  Cases.push_back(SI->getCaseValue(1));
+  for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
+    if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
+      return false;
+    Cases.push_back(SI->getCaseValue(I));
+  }
+  assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
+
+  // Sort the case values, then check if they form a range we can transform.
+  array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
+  for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
+    if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
+      return false;
+  }
+
+  Constant *Offset = ConstantExpr::getNeg(Cases.back());
   Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
 
   Value *Sub = BinaryOperator::CreateAdd(SI->getCondition(), Offset, "off", SI);
diff --git a/test/Transforms/SimplifyCFG/switch-to-icmp.ll b/test/Transforms/SimplifyCFG/switch-to-icmp.ll
new file mode 100644
index 00000000000..2499cdbcd69
--- /dev/null
+++ b/test/Transforms/SimplifyCFG/switch-to-icmp.ll
@@ -0,0 +1,40 @@
+; RUN: opt -S -simplifycfg < %s | FileCheck %s
+
+define zeroext i1 @test1(i32 %x) nounwind readnone ssp noredzone {
+entry:
+ switch i32 %x, label %lor.rhs [
+   i32 2, label %lor.end
+   i32 1, label %lor.end
+   i32 3, label %lor.end
+ ]
+
+lor.rhs:
+ br label %lor.end
+
+lor.end:
+ %0 = phi i1 [ true, %entry ], [ false, %lor.rhs ], [ true, %entry ], [ true, %entry ]
+ ret i1 %0
+
+; CHECK: @test1
+; CHECK: %off = add i32 %x, -1
+; CHECK: %switch = icmp ult i32 %off, 3
+}
+
+define zeroext i1 @test2(i32 %x) nounwind readnone ssp noredzone {
+entry:
+ switch i32 %x, label %lor.rhs [
+   i32 0, label %lor.end
+   i32 1, label %lor.end
+ ]
+
+lor.rhs:
+ br label %lor.end
+
+lor.end:
+ %0 = phi i1 [ true, %entry ], [ false, %lor.rhs ], [ true, %entry ]
+ ret i1 %0
+
+; CHECK: @test2
+; CHECK: %off = add i32 %x, 0
+; CHECK: %switch = icmp ult i32 %off, 2
+}