[llvm] r291296 - [InstSimplify] Optimize away udivs in the presence of range metadata

[David Majnemer via llvm-commits]

Author: majnemer
Date: Fri Jan  6 16:58:02 2017
New Revision: 291296

URL: http://llvm.org/viewvc/llvm-project?rev=291296&view=rev
Log:
[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.

Added:
    llvm/trunk/test/Transforms/InstSimplify/div.ll
Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=291296&r1=291295&r2=291296&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Fri Jan  6 16:58:02 2017
@@ -1106,6 +1106,16 @@ static Value *SimplifyUDivInst(Value *Op
   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;
 }
 

Added: llvm/trunk/test/Transforms/InstSimplify/div.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/div.ll?rev=291296&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/div.ll (added)
+++ llvm/trunk/test/Transforms/InstSimplify/div.ll Fri Jan  6 16:58:02 2017
@@ -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}