rdar://12329730 (2nd part)

This change tries to simmplify E1 = " X >> C1 << C2" into :
  - E2 = "X << (C2 - C1)" if C2 > C1, or
  - E2 = "X >> (C1 - C2)" if C1 > C2, or
  - E2 = X if C1 == C2.

 Reviewed by Nadav. Thanks!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169182 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/InstCombine/InstCombine.h

@@ -327,6 +327,11 @@ private:
   bool SimplifyDemandedBits(Use &U, APInt DemandedMask, 
                             APInt& KnownZero, APInt& KnownOne,
                             unsigned Depth=0);
+  /// Helper routine of SimplifyDemandedUseBits. It tries to simplify demanded
+  /// bit for "r1 = shr x, c1; r2 = shl r1, c2" instruction sequence.
+  Value *SimplifyShrShlDemandedBits(Instruction *Lsr, Instruction *Sftl,
+                                    APInt DemandedMask, APInt &KnownZero,
+                                    APInt &KnownOne);
       
   /// SimplifyDemandedInstructionBits - Inst is an integer instruction that
   /// SimplifyDemandedBits knows about.  See if the instruction has any

lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

@@ -16,9 +16,10 @@
 #include "InstCombine.h"
 #include "llvm/DataLayout.h"
 #include "llvm/IntrinsicInst.h"
+#include "llvm/Support/PatternMatch.h"
 
 using namespace llvm;
-
+using namespace llvm::PatternMatch;
 
 /// ShrinkDemandedConstant - Check to see if the specified operand of the 
 /// specified instruction is a constant integer.  If so, check to see if there
@@ -580,6 +581,17 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     break;
   case Instruction::Shl:
     if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
+      {
+        Value *VarX; ConstantInt *C1;
+        if (match(I->getOperand(0), m_Shr(m_Value(VarX), m_ConstantInt(C1)))) {
+          Instruction *Shr = cast<Instruction>(I->getOperand(0));
+          Value *R = SimplifyShrShlDemandedBits(Shr, I, DemandedMask,
+                                                KnownZero, KnownOne);
+          if (R)
+            return R;
+        }
+      }
+
       uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
       APInt DemandedMaskIn(DemandedMask.lshr(ShiftAmt));
       
@@ -800,6 +812,78 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
   return 0;
 }
 
+/// Helper routine of SimplifyDemandedUseBits. It tries to simplify
+/// "E1 = (X lsr C1) << C2", where the C1 and C2 are constant, into
+/// "E2 = X << (C2 - C1)" or "E2 = X >> (C1 - C2)", depending on the sign
+/// of "C2-C1".
+///
+/// Suppose E1 and E2 are generally different in bits S={bm, bm+1,
+/// ..., bn}, without considering the specific value X is holding.
+/// This transformation is legal iff one of following conditions is hold:
+///  1) All the bit in S are 0, in this case E1 == E2.
+///  2) We don't care those bits in S, per the input DemandedMask.
+///  3) Combination of 1) and 2). Some bits in S are 0, and we don't care the
+///     rest bits.
+///
+/// Currently we only test condition 2).
+///
+/// As with SimplifyDemandedUseBits, it returns NULL if the simplification was
+/// not successful.
+Value *InstCombiner::SimplifyShrShlDemandedBits(Instruction *Shr,
+  Instruction *Shl, APInt DemandedMask, APInt &KnownZero, APInt &KnownOne) {
+
+  unsigned ShlAmt = cast<ConstantInt>(Shl->getOperand(1))->getZExtValue();
+  unsigned ShrAmt = cast<ConstantInt>(Shr->getOperand(1))->getZExtValue();
+
+  KnownOne.clearAllBits();
+  KnownZero = APInt::getBitsSet(KnownZero.getBitWidth(), 0, ShlAmt-1);
+  KnownZero &= DemandedMask;
+
+  if (ShlAmt == 0 || ShrAmt == 0)
+    return 0;
+
+  Value *VarX = Shr->getOperand(0);
+  Type *Ty = VarX->getType();
+
+  APInt BitMask1(Ty->getIntegerBitWidth(), (uint64_t)-1);
+  APInt BitMask2(Ty->getIntegerBitWidth(), (uint64_t)-1);
+
+  bool isLshr = (Shr->getOpcode() == Instruction::LShr);
+  BitMask1 = isLshr ? (BitMask1.lshr(ShrAmt) << ShlAmt) :
+                      (BitMask1.ashr(ShrAmt) << ShlAmt);
+
+  if (ShrAmt <= ShlAmt) {
+    BitMask2 <<= (ShlAmt - ShrAmt);
+  } else {
+    BitMask2 = isLshr ? BitMask2.lshr(ShrAmt - ShlAmt):
+                        BitMask2.ashr(ShrAmt - ShlAmt);
+  }
+
+  // Check if condition-2 (see the comment to this function) is satified.
+  if ((BitMask1 & DemandedMask) == (BitMask2 & DemandedMask)) {
+    if (ShrAmt == ShlAmt)
+      return VarX;
+
+    if (!Shr->hasOneUse())
+      return 0;
+
+    BinaryOperator *New;
+    if (ShrAmt < ShlAmt) {
+      Constant *Amt = ConstantInt::get(VarX->getType(), ShlAmt - ShrAmt);
+      New = BinaryOperator::CreateShl(VarX, Amt);
+      BinaryOperator *Orig = cast<BinaryOperator>(Shl);
+      New->setHasNoSignedWrap(Orig->hasNoSignedWrap());
+      New->setHasNoUnsignedWrap(Orig->hasNoUnsignedWrap());
+    } else {
+      Constant *Amt = ConstantInt::get(VarX->getType(), ShrAmt - ShlAmt);
+      New = BinaryOperator::CreateLShr(VarX, Amt);
+    }
+
+    return InsertNewInstWith(New, *Shl);
+  }
+
+  return 0;
+}
 
 /// SimplifyDemandedVectorElts - The specified value produces a vector with
 /// any number of elements. DemandedElts contains the set of elements that are

test/Transforms/InstCombine/2010-11-01-lshr-mask.ll

@@ -5,8 +5,8 @@
 define i32 @main(i32 %argc) nounwind ssp {
 entry:
   %tmp3151 = trunc i32 %argc to i8
-; CHECK: %tmp3163 = shl i8 %tmp3162, 6
-; CHECK: and i8 %tmp3163, 64
+; CHECK: %tmp3162 = shl i8 %tmp3151, 5
+; CHECK: and i8 %tmp3162, 64
 ; CHECK-NOT: shl
 ; CHECK-NOT: shr
   %tmp3161 = or i8 %tmp3151, -17

test/Transforms/InstCombine/shift.ll

@@ -659,3 +659,79 @@ define i32 @test53(i32 %x) {
 ; CHECK-NEXT: %B = shl nuw i32 %x, 2
 ; CHECK-NEXT: ret i32 %B
 }
+
+define i32 @test54(i32 %x) {
+  %shr2 = lshr i32 %x, 1
+  %shl = shl i32 %shr2, 4
+  %and = and i32 %shl, 16
+  ret i32 %and
+; CHECK: @test54
+; CHECK: shl i32 %x, 3
+}
+
+
+define i32 @test55(i32 %x) {
+  %shr2 = lshr i32 %x, 1
+  %shl = shl i32 %shr2, 4
+  %or = or i32 %shl, 8
+  ret i32 %or
+; CHECK: @test55
+; CHECK: shl i32 %x, 3
+}
+
+define i32 @test56(i32 %x) {
+  %shr2 = lshr i32 %x, 1
+  %shl = shl i32 %shr2, 4
+  %or = or i32 %shl, 7
+  ret i32 %or
+; CHECK: @test56
+; CHECK: shl i32 %shr2, 4
+}
+
+
+define i32 @test57(i32 %x) {
+  %shr = lshr i32 %x, 1
+  %shl = shl i32 %shr, 4
+  %and = and i32 %shl, 16
+  ret i32 %and
+; CHECK: @test57
+; CHECK: shl i32 %x, 3
+}
+
+define i32 @test58(i32 %x) {
+  %shr = lshr i32 %x, 1
+  %shl = shl i32 %shr, 4
+  %or = or i32 %shl, 8
+  ret i32 %or
+; CHECK: @test58
+; CHECK: shl i32 %x, 3
+}
+
+define i32 @test59(i32 %x) {
+  %shr = ashr i32 %x, 1
+  %shl = shl i32 %shr, 4
+  %or = or i32 %shl, 7
+  ret i32 %or
+; CHECK: @test59
+; CHECK: %shl = shl i32 %shr1, 4
+}
+
+
+define i32 @test60(i32 %x) {
+  %shr = ashr i32 %x, 4
+  %shl = shl i32 %shr, 1
+  %or = or i32 %shl, 1
+  ret i32 %or
+; CHECK: @test60
+; CHECK: lshr i32 %x, 3
+}
+
+
+define i32 @test61(i32 %x) {
+  %shr = ashr i32 %x, 4
+  %shl = shl i32 %shr, 1
+  %or = or i32 %shl, 2
+  ret i32 %or
+; CHECK: @test61
+; CHECK: ashr i32 %x, 4
+}

test/Transforms/InstCombine/signext.ll

@@ -82,6 +82,6 @@ entry:
   %sub = add i32 %xor, -67108864                  ; <i32> [#uses=1]
   ret i32 %sub
 ; CHECK: @test8
-; CHECK: %shr = ashr i32 %x, 5
-; CHECK: ret i32 %shr
+; CHECK: %sub = ashr i32 %x, 5
+; CHECK: ret i32 %sub
 }