From 93fad2f404e0448b2e8a31bbe67481ac654ed962 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Fri, 6 Jan 2017 22:58:02 +0000
Subject: [PATCH] [InstSimplify] Optimize away udivs in the presence of range
 metadata

We know that udiv %V, C can be optimized away to 0 if %V is ult C.

llvm-svn: 291296
---
 lib/Analysis/InstructionSimplify.cpp | 10 ++++++++++
 test/Transforms/InstSimplify/div.ll  | 15 +++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 test/Transforms/InstSimplify/div.ll

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 7ae7c4ef939..8da2f0981d0 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1106,6 +1106,16 @@ static Value *SimplifyUDivInst(Value *Op0, Value *Op1, const Query &Q,
   if (Value *V = SimplifyDiv(Instruction::UDiv, Op0, Op1, Q, MaxRecurse))
     return V;
 
+  // udiv %V, C -> 0 if %V < C
+  if (MaxRecurse) {
+    if (Constant *C = dyn_cast_or_null<Constant>(SimplifyICmpInst(
+            ICmpInst::ICMP_ULT, Op0, Op1, Q, MaxRecurse - 1))) {
+      if (C->isAllOnesValue()) {
+        return Constant::getNullValue(Op0->getType());
+      }
+    }
+  }
+
   return nullptr;
 }
 
diff --git a/test/Transforms/InstSimplify/div.ll b/test/Transforms/InstSimplify/div.ll
new file mode 100644
index 00000000000..b8ce34aaa37
--- /dev/null
+++ b/test/Transforms/InstSimplify/div.ll
@@ -0,0 +1,15 @@
+; RUN: opt < %s -instsimplify -S | FileCheck %s
+
+declare i32 @external()
+
+define i32 @div1() {
+; CHECK-LABEL: @div1(
+; CHECK:         [[CALL:%.*]] = call i32 @external(), !range !0
+; CHECK-NEXT:    ret i32 0
+;
+  %call = call i32 @external(), !range !0
+  %urem = udiv i32 %call, 3
+  ret i32 %urem
+}
+
+!0 = !{i32 0, i32 3}