From: Sanjay Patel <spatel@rotateright.com>
Date: Thu, 20 Apr 2017 20:59:02 +0000 (+0000)
Subject: [InstCombine] allow ashr/lshr demanded bits folds with splat constants
X-Git-Tag: llvmorg-5.0.0-rc1~7135
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=fb5b3e773af3e05c7582ea35fbc8b20d8678e649;p=platform%2Fupstream%2Fllvm.git

[InstCombine] allow ashr/lshr demanded bits folds with splat constants

llvm-svn: 300888
---

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index e3a424e..2ba052b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -503,9 +503,9 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
         KnownZero.setLowBits(ShiftAmt);
     }
     break;
-  case Instruction::LShr:
-    // For a logical shift right
-    if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
+  case Instruction::LShr: {
+    const APInt *SA;
+    if (match(I->getOperand(1), m_APInt(SA))) {
       uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
 
       // Unsigned shift right.
@@ -526,7 +526,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
         KnownZero.setHighBits(ShiftAmt);  // high bits known zero.
     }
     break;
-  case Instruction::AShr:
+  }
+  case Instruction::AShr: {
     // If this is an arithmetic shift right and only the low-bit is set, we can
     // always convert this into a logical shr, even if the shift amount is
     // variable.  The low bit of the shift cannot be an input sign bit unless
@@ -543,12 +544,13 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     if (DemandedMask.isSignMask())
       return I->getOperand(0);
 
-    if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
+    const APInt *SA;
+    if (match(I->getOperand(1), m_APInt(SA))) {
       uint32_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
 
       // Signed shift right.
       APInt DemandedMaskIn(DemandedMask.shl(ShiftAmt));
-      // If any of the "high bits" are demanded, we should set the sign bit as
+      // If any of the high bits are demanded, we should set the sign bit as
       // demanded.
       if (DemandedMask.countLeadingZeros() <= ShiftAmt)
         DemandedMaskIn.setSignBit();
@@ -561,6 +563,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
       if (SimplifyDemandedBits(I, 0, DemandedMaskIn, KnownZero, KnownOne,
                                Depth + 1))
         return I;
+
       assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?");
       // Compute the new bits that are at the top now.
       APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
@@ -576,16 +579,16 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
       // are demanded, turn this into an unsigned shift right.
       if (BitWidth <= ShiftAmt || KnownZero[BitWidth-ShiftAmt-1] ||
           (HighBits & ~DemandedMask) == HighBits) {
-        // Perform the logical shift right.
-        BinaryOperator *NewVal = BinaryOperator::CreateLShr(I->getOperand(0),
-                                                            SA, I->getName());
-        NewVal->setIsExact(cast<BinaryOperator>(I)->isExact());
-        return InsertNewInstWith(NewVal, *I);
+        BinaryOperator *LShr = BinaryOperator::CreateLShr(I->getOperand(0),
+                                                          I->getOperand(1));
+        LShr->setIsExact(cast<BinaryOperator>(I)->isExact());
+        return InsertNewInstWith(LShr, *I);
       } else if ((KnownOne & SignMask) != 0) { // New bits are known one.
         KnownOne |= HighBits;
       }
     }
     break;
+  }
   case Instruction::SRem:
     if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
       // X % -1 demands all the bits because we don't want to introduce
diff --git a/llvm/test/Transforms/InstCombine/shift.ll b/llvm/test/Transforms/InstCombine/shift.ll
index 72d361e..d5f4892 100644
--- a/llvm/test/Transforms/InstCombine/shift.ll
+++ b/llvm/test/Transforms/InstCombine/shift.ll
@@ -1270,8 +1270,7 @@ define <2 x i64> @test_64_splat_vec(<2 x i32> %t) {
 
 define <2 x i8> @ashr_demanded_bits_splat(<2 x i8> %x) {
 ; CHECK-LABEL: @ashr_demanded_bits_splat(
-; CHECK-NEXT:    [[AND:%.*]] = and <2 x i8> %x, <i8 -128, i8 -128>
-; CHECK-NEXT:    [[SHR:%.*]] = ashr exact <2 x i8> [[AND]], <i8 7, i8 7>
+; CHECK-NEXT:    [[SHR:%.*]] = ashr <2 x i8> %x, <i8 7, i8 7>
 ; CHECK-NEXT:    ret <2 x i8> [[SHR]]
 ;
   %and = and <2 x i8> %x, <i8 128, i8 128>
@@ -1281,8 +1280,7 @@ define <2 x i8> @ashr_demanded_bits_splat(<2 x i8> %x) {
 
 define <2 x i8> @lshr_demanded_bits_splat(<2 x i8> %x) {
 ; CHECK-LABEL: @lshr_demanded_bits_splat(
-; CHECK-NEXT:    [[AND:%.*]] = and <2 x i8> %x, <i8 -128, i8 -128>
-; CHECK-NEXT:    [[SHR:%.*]] = lshr exact <2 x i8> [[AND]], <i8 7, i8 7>
+; CHECK-NEXT:    [[SHR:%.*]] = lshr <2 x i8> %x, <i8 7, i8 7>
 ; CHECK-NEXT:    ret <2 x i8> [[SHR]]
 ;
   %and = and <2 x i8> %x, <i8 128, i8 128>
diff --git a/llvm/test/Transforms/InstCombine/vector-casts.ll b/llvm/test/Transforms/InstCombine/vector-casts.ll
index 643ab6c..2197c25 100644
--- a/llvm/test/Transforms/InstCombine/vector-casts.ll
+++ b/llvm/test/Transforms/InstCombine/vector-casts.ll
@@ -15,9 +15,9 @@ define <2 x i1> @test1(<2 x i64> %a) {
 ; The ashr turns into an lshr.
 define <2 x i64> @test2(<2 x i64> %a) {
 ; CHECK-LABEL: @test2(
-; CHECK-NEXT:    [[B:%.*]] = and <2 x i64> %a, <i64 65535, i64 65535>
-; CHECK-NEXT:    [[T:%.*]] = lshr <2 x i64> [[B]], <i64 1, i64 1>
-; CHECK-NEXT:    ret <2 x i64> [[T]]
+; CHECK-NEXT:    [[B:%.*]] = and <2 x i64> %a, <i64 65534, i64 65534>
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr exact <2 x i64> [[B]], <i64 1, i64 1>
+; CHECK-NEXT:    ret <2 x i64> [[TMP1]]
 ;
   %b = and <2 x i64> %a, <i64 65535, i64 65535>
   %t = ashr <2 x i64> %b, <i64 1, i64 1>