From 639570c3117aaabb0c97b34a9bf05d09f8903ef4 Mon Sep 17 00:00:00 2001
From: Nadav Rotem <nrotem@apple.com>
Date: Thu, 30 Aug 2012 11:23:20 +0000
Subject: [PATCH] It is illegal to transform (sdiv (ashr X c1) c2)  -> (sdiv x
 (2^c1 * c2)), because C always rounds towards zero.

Thanks Dirk and Ben.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162899 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../InstCombine/InstCombineMulDivRem.cpp      | 10 --------
 .../InstCombine/2012-08-28-udiv_ashl.ll       | 25 -------------------
 2 files changed, 35 deletions(-)

diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 2119115ca71..003dc55a03f 100644
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -543,16 +543,6 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
                                           ConstantExpr::getNeg(RHS));
   }
 
-  // Sdiv ((Ashl x, C1) , C2) ->  x / (C2 * 1<<C1);
-  if (ConstantInt *C2 = dyn_cast<ConstantInt>(Op1)) {
-    Value *X;
-    ConstantInt *C1;
-    if (match(Op0, m_AShr(m_Value(X), m_ConstantInt(C1)))) {
-      APInt NC = C2->getValue().shl(C1->getLimitedValue(C1->getBitWidth()-1));
-      return BinaryOperator::CreateSDiv(X, Builder->getInt(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
index a35a816219a..4efaf8c1725 100644
--- a/test/Transforms/InstCombine/2012-08-28-udiv_ashl.ll
+++ b/test/Transforms/InstCombine/2012-08-28-udiv_ashl.ll
@@ -15,15 +15,6 @@ entry:
   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
@@ -59,22 +50,6 @@ define i80 @udiv_i80(i80 %x) {
   ret i80 %div1
 }
 
-; CHECK: @sdiv_i80
-; CHECK: sdiv i80 %x, 400
-; CHECK: ret
-define i80 @sdiv_i80(i80 %x) {
-  %div = ashr i80 %x, 2
-  %div1 = sdiv i80 %div, 100
-  ret i80 %div1
-}
-
-
-define i32 @no_crash_notconst_sdiv(i32 %x, i32 %notconst) {
-  %div = ashr i32 %x, %notconst
-  %div1 = sdiv i32 %div, 100
-  ret i32 %div1
-}
-
 define i32 @no_crash_notconst_udiv(i32 %x, i32 %notconst) {
   %div = lshr i32 %x, %notconst
   %div1 = udiv i32 %div, 100