[llvm] r257773 - Revert "[ValueTracking] Understand more select patterns in ComputeKnownBits"

[James Molloy via llvm-commits]

Author: jamesm
Date: Thu Jan 14 09:49:32 2016
New Revision: 257773

URL: http://llvm.org/viewvc/llvm-project?rev=257773&view=rev
Log:
Revert "[ValueTracking] Understand more select patterns in ComputeKnownBits"

This reverts commit r257769. Backing this out because of stage2 failures.

Removed:
    llvm/trunk/test/Analysis/ValueTracking/select-maxbits.ll
Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=257773&r1=257772&r2=257773&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Thu Jan 14 09:49:32 2016
@@ -1140,52 +1140,14 @@ static void computeKnownBitsFromOperator
     KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ);
     break;
   }
-  case Instruction::Select: {
+  case Instruction::Select:
     computeKnownBits(I->getOperand(2), KnownZero, KnownOne, DL, Depth + 1, Q);
     computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, DL, Depth + 1, Q);
 
     // Only known if known in both the LHS and RHS.
     KnownOne &= KnownOne2;
     KnownZero &= KnownZero2;
-
-    // There are several cmp+select patterns that ensure their result will be no
-    // greater than a constant. Detect a number of these.
-    Value *X, *Y;
-    ConstantInt *C1, *C2;
-    ICmpInst::Predicate Pred;
-
-    auto IsLessThanOrEqualTo = [](Value *X, Value *Y) {
-      if (X == Y)
-        return true;
-      Value *M1, *M2;
-      ConstantInt *C1, *C2;
-      if (!match(X, m_NSWAdd(m_Value(M1), m_ConstantInt(C1))))
-        C1 = nullptr;
-      if (!match(Y, m_NSWAdd(m_Value(M2), m_ConstantInt(C2))))
-        C2 = nullptr;
-      if (C1 && M1 == Y && C1->isNegative())
-        return true;
-      if (C2 && M2 == X && !C2->isNegative())
-        return true;
-      if (C1 && C2 && M1 == M2 && !C1->isNegative() && !C2->isNegative() &&
-          C1->getValue().ule(C2->getValue()))
-        return true;
-      return false;
-    };
-
-    // (select (icmp ugt X, C1), C2, Y)
-    //   if Y <= X and C2 <= C1
-    //   then maximum value = C1.
-    if (match(I, m_Select(m_ICmp(Pred, m_Value(X), m_ConstantInt(C1)),
-                          m_ConstantInt(C2), m_Value(Y)))) {
-      if (Pred == ICmpInst::ICMP_UGT && IsLessThanOrEqualTo(Y, X) &&
-          C2->getValue().ule(C1->getValue())) {
-        auto V = cast<ConstantInt>(C1)->getValue() - 1;
-        KnownZero = ~APInt::getLowBitsSet(V.getBitWidth(), V.getActiveBits());
-      }
-    }
     break;
-  }
   case Instruction::FPTrunc:
   case Instruction::FPExt:
   case Instruction::FPToUI:

Removed: llvm/trunk/test/Analysis/ValueTracking/select-maxbits.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ValueTracking/select-maxbits.ll?rev=257772&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/ValueTracking/select-maxbits.ll (original)
+++ llvm/trunk/test/Analysis/ValueTracking/select-maxbits.ll (removed)
@@ -1,62 +0,0 @@
-; RUN: opt -S -instsimplify < %s | FileCheck %s
-
-; CHECK-LABEL: @one
-define i32 @one(i32 %a) {
-; CHECK: ret i32 0
-  %b = icmp ugt i32 %a, 5
-  %c = select i1 %b, i32 2, i32 %a
-  %d = lshr i32 %c, 24
-  ret i32 %d
-}
-
-; CHECK-LABEL: @two
-define i32 @two(i32 %a) {
-; CHECK: ret i32 0
-  %x = add nsw i32 %a, 4
-  %b = icmp ugt i32 %x, 5
-  %c = select i1 %b, i32 2, i32 %a
-  %d = lshr i32 %c, 24
-  ret i32 %d
-}
-
-; CHECK-LABEL: @two_no_nsw
-define i32 @two_no_nsw(i32 %a) {
-; CHECK: ret i32 %d
-  %x = add i32 %a, 4
-  %b = icmp ugt i32 %x, 5
-  %c = select i1 %b, i32 2, i32 %a
-  %d = lshr i32 %c, 24
-  ret i32 %d
-}
-
-; CHECK-LABEL: @three
-define i32 @three(i32 %a) {
-; CHECK: ret i32 0
-  %x = add nsw i32 %a, -4
-  %b = icmp ugt i32 %a, 5
-  %c = select i1 %b, i32 2, i32 %x
-  %d = lshr i32 %c, 24
-  ret i32 %d
-}
-
-; CHECK-LABEL: @four
-define i32 @four(i32 %a) {
-; CHECK: ret i32 0
-  %x = add nsw i32 %a, 42
-  %y = add nsw i32 %a, 64
-  %b = icmp ugt i32 %y, 5
-  %c = select i1 %b, i32 2, i32 %x
-  %d = lshr i32 %c, 24
-  ret i32 %d
-}
-
-; CHECK-LABEL: @four_swapped
-define i32 @four_swapped(i32 %a) {
-; CHECK: ret i32 %d
-  %x = add nsw i32 %a, 42
-  %y = add nsw i32 %a, 64
-  %b = icmp ugt i32 %x, 5
-  %c = select i1 %b, i32 2, i32 %y
-  %d = lshr i32 %c, 24
-  ret i32 %d
-}
\ No newline at end of file