From 9582c96aefcdb0cf6cad3e233723ee232025878c Mon Sep 17 00:00:00 2001
From: Nadav Rotem <nrotem@apple.com>
Date: Tue, 28 Aug 2012 10:01:43 +0000
Subject: [PATCH] Teach InstCombine to canonicalize  [SU]div+[AL]shl patterns.

For example:
  %1 = lshr i32 %x, 2
  %2 = udiv i32 %1, 100

rdar://12182093

llvm-svn: 162743
---
 .../InstCombine/InstCombineMulDivRem.cpp      | 20 ++++++++
 .../InstCombine/2012-08-28-udiv_ashl.ll       | 50 +++++++++++++++++++
 .../InstCombine/udiv-simplify-bug-1.ll        |  4 +-
 3 files changed, 72 insertions(+), 2 deletions(-)
 create mode 100644 test/Transforms/InstCombine/2012-08-28-udiv_ashl.ll

diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 35a0bbb7614..e104a0a9798 100644
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -462,6 +462,16 @@ Instruction *InstCombiner::visitUDiv(BinaryOperator &I) {
     }
   }
 
+  // Udiv ((Lshl x, c1) , c2) ->  x / (C1 * 1<<C2);
+  if (Constant *C = dyn_cast<Constant>(Op1)) {
+    Value *X = 0, *C1 = 0;
+    if (match(Op0, m_LShr(m_Value(X), m_Value(C1)))) {
+      uint64_t NC = cast<ConstantInt>(C)->getZExtValue() *
+                    (1<< cast<ConstantInt>(C1)->getZExtValue());
+      return BinaryOperator::CreateUDiv(X, ConstantInt::get(I.getType(), NC));
+    }
+  }
+
   // X udiv (C1 << N), where C1 is "1<<C2"  -->  X >> (N+C2)
   { const APInt *CI; Value *N;
     if (match(Op1, m_Shl(m_Power2(CI), m_Value(N))) ||
@@ -533,6 +543,16 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
                                           ConstantExpr::getNeg(RHS));
   }
 
+  // Sdiv ((Ashl x, c1) , c2) ->  x / (C1 * 1<<C2);
+  if (Constant *C = dyn_cast<Constant>(Op1)) {
+    Value *X = 0, *C1 = 0;
+    if (match(Op0, m_AShr(m_Value(X), m_Value(C1)))) {
+      uint64_t NC = cast<ConstantInt>(C)->getZExtValue() *
+                    (1<< cast<ConstantInt>(C1)->getZExtValue());
+      return BinaryOperator::CreateSDiv(X, ConstantInt::get(I.getType(), NC));
+    }
+  }
+
   // If the sign bits of both operands are zero (i.e. we can prove they are
   // unsigned inputs), turn this into a udiv.
   if (I.getType()->isIntegerTy()) {
diff --git a/test/Transforms/InstCombine/2012-08-28-udiv_ashl.ll b/test/Transforms/InstCombine/2012-08-28-udiv_ashl.ll
new file mode 100644
index 00000000000..9f52119248e
--- /dev/null
+++ b/test/Transforms/InstCombine/2012-08-28-udiv_ashl.ll
@@ -0,0 +1,50 @@
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+; rdar://12182093
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.8.0"
+
+; CHECK: @udiv400
+; CHECK: udiv i32 %x, 400
+; CHECK: ret
+define i32 @udiv400(i32 %x) {
+entry:
+  %div = lshr i32 %x, 2
+  %div1 = udiv i32 %div, 100
+  ret i32 %div1
+}
+
+; CHECK: @sdiv400
+; CHECK: sdiv i32 %x, 400
+; CHECK: ret
+define i32 @sdiv400(i32 %x) {
+entry:
+  %div = ashr i32 %x, 2
+  %div1 = sdiv i32 %div, 100
+  ret i32 %div1
+}
+
+; CHECK: @udiv400_no
+; CHECK: ashr
+; CHECK: div
+; CHECK: ret
+define i32 @udiv400_no(i32 %x) {
+entry:
+  %div = ashr i32 %x, 2
+  %div1 = udiv i32 %div, 100
+  ret i32 %div1
+}
+
+; CHECK: @sdiv400_yes
+; CHECK: udiv i32 %x, 400
+; CHECK: ret
+define i32 @sdiv400_yes(i32 %x) {
+entry:
+  %div = lshr i32 %x, 2
+  ; The sign bits of both operands are zero (i.e. we can prove they are
+  ; unsigned inputs), turn this into a udiv.
+  ; Next, optimize this just like sdiv.
+  %div1 = sdiv i32 %div, 100
+  ret i32 %div1
+}
diff --git a/test/Transforms/InstCombine/udiv-simplify-bug-1.ll b/test/Transforms/InstCombine/udiv-simplify-bug-1.ll
index d95e8f83590..74f2fdd7cc6 100644
--- a/test/Transforms/InstCombine/udiv-simplify-bug-1.ll
+++ b/test/Transforms/InstCombine/udiv-simplify-bug-1.ll
@@ -6,9 +6,9 @@
 ; The udiv instructions shouldn't be optimized away, and the
 ; sext instructions should be optimized to zext.
 
-define i64 @bar(i32 %x) nounwind {
+define i64 @bar(i32 %x, i32 %g) nounwind {
   %y = lshr i32 %x, 30
-  %r = udiv i32 %y, 3
+  %r = udiv i32 %y, %g
   %z = sext i32 %r to i64
   ret i64 %z
 }