[InstCombine] move folds for shift-shift pairs; NFCI

Although this is 'no-functional-change-intended', I'm adding tests
for shl-shl and lshr-lshr pairs because there is no existing test
coverage for those folds.

It seems like we should be able to remove some code from foldShiftedShift()
at this point because we're handling those patterns on the general path.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293814 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp
index 4b6879255636d37bbe9b3cf1594a9fc2c2b45391..ab8ba9e4be00b3564248be058737901c8c6cc64b 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -309,41 +309,6 @@ static Value *getShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
   }
 }
 
-/// Try to fold (X << C1) << C2, where the shifts are some combination of
-/// shl/ashr/lshr.
-static Instruction *
-foldShiftByConstOfShiftByConst(BinaryOperator &I, const APInt *COp1,
-                               InstCombiner::BuilderTy *Builder) {
-  Value *Op0 = I.getOperand(0);
-  unsigned TypeBits = Op0->getType()->getScalarSizeInBits();
-
-  // Find out if this is a shift of a shift by a constant.
-  BinaryOperator *ShiftOp = dyn_cast<BinaryOperator>(Op0);
-  if (!ShiftOp || !ShiftOp->isShift())
-    return nullptr;
-
-  const APInt *ShAmt1;
-  if (!match(ShiftOp->getOperand(1), m_APInt(ShAmt1)))
-    return nullptr;
-
-  // Check for (X << c1) << c2  and  (X >> c1) >> c2
-  if (I.getOpcode() == ShiftOp->getOpcode()) {
-    unsigned AmtSum = (*ShAmt1 + *COp1).getZExtValue();
-    // If this is an oversized composite shift, then unsigned shifts become
-    // zero (handled in InstSimplify) and ashr saturates.
-    if (AmtSum >= TypeBits) {
-      if (I.getOpcode() != Instruction::AShr)
-        return nullptr;
-      AmtSum = TypeBits - 1; // Saturate to 31 for i32 ashr.
-    }
-
-    return BinaryOperator::Create(I.getOpcode(), ShiftOp->getOperand(0),
-                                  ConstantInt::get(I.getType(), AmtSum));
-  }
-
-  return nullptr;
-}
-
 Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
                                                BinaryOperator &I) {
   bool isLeftShift = I.getOpcode() == Instruction::Shl;
@@ -553,9 +518,6 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
     }
   }
 
-  if (Instruction *Folded = foldShiftByConstOfShiftByConst(I, Op1C, Builder))
-    return Folded;
-
   return nullptr;
 }
 
@@ -598,10 +560,10 @@ Instruction *InstCombiner::visitShl(BinaryOperator &I) {
     // arithmetic expressions are still recognizable by scalar evolution.
     // The inexact versions are deferred to DAGCombine, so we don't hide shl
     // behind a bit mask.
-    const APInt *ShrOp1;
-    if (match(Op0, m_CombineOr(m_Exact(m_LShr(m_Value(X), m_APInt(ShrOp1))),
-                               m_Exact(m_AShr(m_Value(X), m_APInt(ShrOp1)))))) {
-      unsigned ShrAmt = ShrOp1->getZExtValue();
+    const APInt *ShOp1;
+    if (match(Op0, m_CombineOr(m_Exact(m_LShr(m_Value(X), m_APInt(ShOp1))),
+                               m_Exact(m_AShr(m_Value(X), m_APInt(ShOp1)))))) {
+      unsigned ShrAmt = ShOp1->getZExtValue();
       if (ShrAmt < ShAmt) {
         // If C1 < C2: (X >>?,exact C1) << C2 --> X << (C2 - C1)
         Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - ShrAmt);
@@ -620,6 +582,14 @@ Instruction *InstCombiner::visitShl(BinaryOperator &I) {
       }
     }
 
+    if (match(Op0, m_Shl(m_Value(X), m_APInt(ShOp1)))) {
+      unsigned AmtSum = ShAmt + ShOp1->getZExtValue();
+      // Oversized shifts are simplified to zero in InstSimplify.
+      if (AmtSum < BitWidth)
+        // (X << C1) << C2 --> X << (C1 + C2)
+        return BinaryOperator::CreateShl(X, ConstantInt::get(Ty, AmtSum));
+    }
+
     // If the shifted-out value is known-zero, then this is a NUW shift.
     if (!I.hasNoUnsignedWrap() &&
         MaskedValueIsZero(Op0, APInt::getHighBitsSet(BitWidth, ShAmt), 0, &I)) {
@@ -675,9 +645,9 @@ Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
     }
 
     Value *X;
-    const APInt *ShlAmtAPInt;
-    if (match(Op0, m_Shl(m_Value(X), m_APInt(ShlAmtAPInt)))) {
-      unsigned ShlAmt = ShlAmtAPInt->getZExtValue();
+    const APInt *ShOp1;
+    if (match(Op0, m_Shl(m_Value(X), m_APInt(ShOp1)))) {
+      unsigned ShlAmt = ShOp1->getZExtValue();
       if (ShlAmt < ShAmt) {
         Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - ShlAmt);
         if (cast<BinaryOperator>(Op0)->hasNoUnsignedWrap()) {
@@ -710,6 +680,14 @@ Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
       return BinaryOperator::CreateAnd(X, ConstantInt::get(Ty, Mask));
     }
 
+    if (match(Op0, m_LShr(m_Value(X), m_APInt(ShOp1)))) {
+      unsigned AmtSum = ShAmt + ShOp1->getZExtValue();
+      // Oversized shifts are simplified to zero in InstSimplify.
+      if (AmtSum < BitWidth)
+        // (X >>u C1) >>u C2 --> X >>u (C1 + C2)
+        return BinaryOperator::CreateLShr(X, ConstantInt::get(Ty, AmtSum));
+    }
+
     // If the shifted-out value is known-zero, then this is an exact shift.
     if (!I.isExact() &&
         MaskedValueIsZero(Op0, APInt::getLowBitsSet(BitWidth, ShAmt), 0, &I)) {
@@ -747,9 +725,9 @@ Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
 
     // We can't handle (X << C1) >>s C2. It shifts arbitrary bits in. However,
     // we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits.
-    const APInt *ShlAmtAPInt;
-    if (match(Op0, m_NSWShl(m_Value(X), m_APInt(ShlAmtAPInt)))) {
-      unsigned ShlAmt = ShlAmtAPInt->getZExtValue();
+    const APInt *ShOp1;
+    if (match(Op0, m_NSWShl(m_Value(X), m_APInt(ShOp1)))) {
+      unsigned ShlAmt = ShOp1->getZExtValue();
       if (ShlAmt < ShAmt) {
         // (X <<nsw C1) >>s C2 --> X >>s (C2 - C1)
         Constant *ShiftDiff = ConstantInt::get(Ty, ShAmt - ShlAmt);
@@ -766,6 +744,14 @@ Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
       }
     }
 
+    if (match(Op0, m_AShr(m_Value(X), m_APInt(ShOp1)))) {
+      unsigned AmtSum = ShAmt + ShOp1->getZExtValue();
+      // Oversized arithmetic shifts replicate the sign bit.
+      AmtSum = std::min(AmtSum, BitWidth - 1);
+      // (X >>s C1) >>s C2 --> X >>s (C1 + C2)
+      return BinaryOperator::CreateAShr(X, ConstantInt::get(Ty, AmtSum));
+    }
+
     // If the shifted-out value is known-zero, then this is an exact shift.
     if (!I.isExact() &&
         MaskedValueIsZero(Op0, APInt::getLowBitsSet(BitWidth, ShAmt), 0, &I)) {

diff --git a/test/Transforms/InstCombine/apint-shift.ll b/test/Transforms/InstCombine/apint-shift.ll
index fc1934b576f5cfa8f1e866c93c7b0be85df5d8ca..f1276beec9fc58770a10ecd8ad977451b075f469 100644 (file)
--- a/test/Transforms/InstCombine/apint-shift.ll
+++ b/test/Transforms/InstCombine/apint-shift.ll
@@ -126,6 +126,32 @@ define <2 x i19> @lshr_lshr_splat_vec(<2 x i19> %X) {
   ret <2 x i19> %sh2
 }
 
+define i9 @multituse_lshr_lshr(i9 %x) {
+; CHECK-LABEL: @multituse_lshr_lshr(
+; CHECK-NEXT:    [[SH1:%.*]] = lshr i9 %x, 2
+; CHECK-NEXT:    [[SH2:%.*]] = lshr i9 %x, 5
+; CHECK-NEXT:    [[MUL:%.*]] = mul i9 [[SH1]], [[SH2]]
+; CHECK-NEXT:    ret i9 [[MUL]]
+;
+  %sh1 = lshr i9 %x, 2
+  %sh2 = lshr i9 %sh1, 3
+  %mul = mul i9 %sh1, %sh2
+  ret i9 %mul
+}
+
+define <2 x i9> @multiuse_lshr_lshr_splat(<2 x i9> %x) {
+; CHECK-LABEL: @multiuse_lshr_lshr_splat(
+; CHECK-NEXT:    [[SH1:%.*]] = lshr <2 x i9> %x, <i9 2, i9 2>
+; CHECK-NEXT:    [[SH2:%.*]] = lshr <2 x i9> %x, <i9 5, i9 5>
+; CHECK-NEXT:    [[MUL:%.*]] = mul <2 x i9> [[SH1]], [[SH2]]
+; CHECK-NEXT:    ret <2 x i9> [[MUL]]
+;
+  %sh1 = lshr <2 x i9> %x, <i9 2, i9 2>
+  %sh2 = lshr <2 x i9> %sh1, <i9 3, i9 3>
+  %mul = mul <2 x i9> %sh1, %sh2
+  ret <2 x i9> %mul
+}
+
 ; Two left shifts in the same direction:
 ; shl (shl X, C1), C2 -->  shl X, C1 + C2
 
@@ -139,6 +165,32 @@ define <2 x i19> @shl_shl_splat_vec(<2 x i19> %X) {
   ret <2 x i19> %sh2
 }
 
+define i42 @multiuse_shl_shl(i42 %x) {
+; CHECK-LABEL: @multiuse_shl_shl(
+; CHECK-NEXT:    [[SH1:%.*]] = shl i42 %x, 8
+; CHECK-NEXT:    [[SH2:%.*]] = shl i42 %x, 17
+; CHECK-NEXT:    [[MUL:%.*]] = mul i42 [[SH1]], [[SH2]]
+; CHECK-NEXT:    ret i42 [[MUL]]
+;
+  %sh1 = shl i42 %x, 8
+  %sh2 = shl i42 %sh1, 9
+  %mul = mul i42 %sh1, %sh2
+  ret i42 %mul
+}
+
+define <2 x i42> @mulituse_shl_shl_splat(<2 x i42> %x) {
+; CHECK-LABEL: @mulituse_shl_shl_splat(
+; CHECK-NEXT:    [[SH1:%.*]] = shl <2 x i42> %x, <i42 8, i42 8>
+; CHECK-NEXT:    [[SH2:%.*]] = shl <2 x i42> %x, <i42 17, i42 17>
+; CHECK-NEXT:    [[MUL:%.*]] = mul <2 x i42> [[SH1]], [[SH2]]
+; CHECK-NEXT:    ret <2 x i42> [[MUL]]
+;
+  %sh1 = shl <2 x i42> %x, <i42 8, i42 8>
+  %sh2 = shl <2 x i42> %sh1, <i42 9, i42 9>
+  %mul = mul <2 x i42> %sh1, %sh2
+  ret <2 x i42> %mul
+}
+
 ; Equal shift amounts in opposite directions become bitwise 'and':
 ; lshr (shl X, C), C --> and X, C'