From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Sat, 7 Jun 2014 04:12:35 +0000 (+0000)
Subject: Revert 209903 and 210040.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=68caf1727f809804b4fcfcefd475490fef9d304d;p=oota-llvm.git

Revert 209903 and 210040.

The messages were

 "PR19753: Optimize comparisons with "ashr exact" of a constanst."
 "Added support to optimize comparisons with "lshr exact" of a constant."

They were not correctly handling signed/unsigned operation differences,
causing pr19958.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210393 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 13a5cd96f7b..d98f966f8ca 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2318,32 +2318,6 @@ static bool swapMayExposeCSEOpportunities(const Value * Op0,
   return GlobalSwapBenefits > 0;
 }
 
-// Helper function to check whether Op represents a lshr/ashr exact
-// instruction. For example:
-// (icmp (ashr exact const2, A), const1) -> icmp A, Log2(const2/const1)
-// Here if Op represents -> (ashr exact const2, A), and CI represents
-// const1, we compute Quotient as const2/const1.
-
-static bool checkShrExact(Value *Op, APInt &Quotient, const ConstantInt *CI,
-                          Value *&A) {
-
-  ConstantInt *CI2;
-  if (match(Op, m_AShr(m_ConstantInt(CI2), m_Value(A))) &&
-      (cast<BinaryOperator>(Op)->isExact())) {
-    Quotient = CI2->getValue().sdiv(CI->getValue());
-    return true;
-  }
-
-  // Handle the case for lhsr.
-  if (match(Op, m_LShr(m_ConstantInt(CI2), m_Value(A))) &&
-      (cast<BinaryOperator>(Op)->isExact())) {
-    Quotient = CI2->getValue().udiv(CI->getValue());
-    return true;
-  }
-
-  return false;
-}
-
 Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
   bool Changed = false;
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
@@ -2465,20 +2439,6 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
       return new ICmpInst(I.getPredicate(), A, B);
     }
 
-    // PR19753:
-    // (icmp (ashr exact const2, A), const1) -> icmp A, Log2(const2/const1)
-    // Cases where const1 doesn't divide const2 exactly or Quotient is not
-    // exact of log2 are handled by SimplifyICmpInst call above where we
-    // return false. Similar for lshr.
-    {
-      APInt Quotient;
-      if (checkShrExact(Op0, Quotient, CI, A)) {
-        unsigned shift = Quotient.logBase2();
-        return new ICmpInst(I.getPredicate(), A,
-                            ConstantInt::get(A->getType(), shift));
-      }
-    }
-
     // If we have an icmp le or icmp ge instruction, turn it into the
     // appropriate icmp lt or icmp gt instruction.  This allows us to rely on
     // them being folded in the code below.  The SimplifyICmpInst code has
diff --git a/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll
index 8e107edd762..560fbcbfae9 100644
--- a/test/Transforms/InstCombine/icmp.ll
+++ b/test/Transforms/InstCombine/icmp.ll
@@ -1382,19 +1382,3 @@ define i1 @icmp_neg_cst_slt(i32 %a) {
   %2 = icmp slt i32 %1, -10
   ret i1 %2
 }
-
-; CHECK-LABEL: @exact_ashr_eq_false
-; CHECK-NEXT: icmp eq i32 %a, 1
-define i1 @exact_ashr_eq_false(i32 %a) {
-  %shr = ashr exact i32 -30, %a
-  %cmp = icmp eq i32 %shr, -15
-  ret i1 %cmp
-}
-
-; CHECK-LABEL: @exact_lhsr
-; CHECK-NEXT: icmp eq i32 %a, 3
-define i1 @exact_lhsr(i32 %a) {
-  %shr = lshr exact i32 80, %a
-  %cmp = icmp eq i32 %shr, 10
-  ret i1 %cmp
-}