From 56f8a7c1a4906a6c69a61781e17c3d01e5abfedb Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Fri, 6 Jan 2017 21:23:51 +0000
Subject: [PATCH] [InstSimplify] Optimize away urems in the presence of range
 metadata

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

llvm-svn: 291282
---
 lib/Analysis/InstructionSimplify.cpp          | 10 ++++
 .../InstCombine/urem-simplify-bug.ll          | 46 ++++++++++---------
 test/Transforms/InstSimplify/rem.ll           | 14 ++++++
 3 files changed, 49 insertions(+), 21 deletions(-)

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index b4686a1ff17..7ae7c4ef939 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1247,6 +1247,16 @@ static Value *SimplifyURemInst(Value *Op0, Value *Op1, const Query &Q,
   if (Value *V = SimplifyRem(Instruction::URem, Op0, Op1, Q, MaxRecurse))
     return V;
 
+  // urem %V, C -> %V 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 Op0;
+      }
+    }
+  }
+
   return nullptr;
 }
 
diff --git a/test/Transforms/InstCombine/urem-simplify-bug.ll b/test/Transforms/InstCombine/urem-simplify-bug.ll
index 1220dfdc77f..4f18f359854 100644
--- a/test/Transforms/InstCombine/urem-simplify-bug.ll
+++ b/test/Transforms/InstCombine/urem-simplify-bug.ll
@@ -1,32 +1,36 @@
-; RUN: opt < %s -instcombine -S | grep "= or i32 %x, -5"
+; RUN: opt < %s -instcombine -S | FileCheck %s
 
-@.str = internal constant [5 x i8] c"foo\0A\00"		; <[5 x i8]*> [#uses=1]
-@.str1 = internal constant [5 x i8] c"bar\0A\00"		; <[5 x i8]*> [#uses=1]
+@.str = internal constant [5 x i8] c"foo\0A\00"
+@.str1 = internal constant [5 x i8] c"bar\0A\00"
 
 define i32 @main() nounwind  {
 entry:
-	%x = call i32 @func_11( ) nounwind 		; <i32> [#uses=1]
-	%tmp3 = or i32 %x, -5		; <i32> [#uses=1]
-	%tmp5 = urem i32 251, %tmp3		; <i32> [#uses=1]
-	%tmp6 = icmp ne i32 %tmp5, 0		; <i1> [#uses=1]
-	%tmp67 = zext i1 %tmp6 to i32		; <i32> [#uses=1]
-	%tmp9 = urem i32 %tmp67, 95		; <i32> [#uses=1]
-	%tmp10 = and i32 %tmp9, 1		; <i32> [#uses=1]
-	%tmp12 = icmp eq i32 %tmp10, 0		; <i1> [#uses=1]
-	br i1 %tmp12, label %bb14, label %bb
+  %x = call i32 @func_11() nounwind
+  %tmp3 = or i32 %x, -5
+  %tmp5 = urem i32 251, %tmp3
+  %tmp6 = icmp ne i32 %tmp5, 0
+  %tmp67 = zext i1 %tmp6 to i32
+  %tmp9 = urem i32 %tmp67, 95
+  %tmp10 = and i32 %tmp9, 1
+  %tmp12 = icmp eq i32 %tmp10, 0
+  br i1 %tmp12, label %bb14, label %bb
 
-bb:		; preds = %entry
-	br label %bb15
+bb:
+  br label %bb15
 
-bb14:		; preds = %entry
-	br label %bb15
+bb14:
+  br label %bb15
 
-bb15:		; preds = %bb14, %bb
-	%iftmp.0.0 = phi i8* [ getelementptr ([5 x i8], [5 x i8]* @.str1, i32 0, i32 0), %bb14 ], [ getelementptr ([5 x i8], [5 x i8]* @.str, i32 0, i32 0), %bb ]		; <i8*> [#uses=1]
-	%tmp17 = call i32 (i8*, ...) @printf( i8* %iftmp.0.0 ) nounwind 		; <i32> [#uses=0]
-	ret i32 0
+bb15:
+  %iftmp.0.0 = phi i8* [ getelementptr ([5 x i8], [5 x i8]* @.str1, i32 0, i32 0), %bb14 ], [ getelementptr ([5 x i8], [5 x i8]* @.str, i32 0, i32 0), %bb ]
+  %tmp17 = call i32 (i8*, ...) @printf(i8* %iftmp.0.0) nounwind
+  ret i32 0
 }
 
+; CHECK-LABEL: define i32 @main(
+; CHECK: call i32 @func_11()
+; CHECK-NEXT: br i1 false, label %bb14, label %bb
+
 declare i32 @func_11()
 
-declare i32 @printf(i8*, ...) nounwind 
+declare i32 @printf(i8*, ...) nounwind
diff --git a/test/Transforms/InstSimplify/rem.ll b/test/Transforms/InstSimplify/rem.ll
index df3f659b782..c73d34346de 100644
--- a/test/Transforms/InstSimplify/rem.ll
+++ b/test/Transforms/InstSimplify/rem.ll
@@ -49,3 +49,17 @@ define i32 @rem3(i32 %x, i32 %n) {
  %mod1 = urem i32 %mod, %n
  ret i32 %mod1
 }
+
+declare i32 @external()
+
+define i32 @rem4() {
+; CHECK-LABEL: @rem4(
+; CHECK:         [[CALL:%.*]] = call i32 @external(), !range !0
+; CHECK-NEXT:    ret i32 [[CALL]]
+;
+  %call = call i32 @external(), !range !0
+  %urem = urem i32 %call, 3
+  ret i32 %urem
+}
+
+!0 = !{i32 0, i32 3}