Revert "Handle non-power-of-2 divisors in division-like operations", "A64 tweaks for division-like …

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index d86e1b6376a27bc0d153490ed384426929bf9ff4..6b38fd13ba8846739e243561393d7af13dfbcdc6 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -1144,35 +1144,6 @@ void LCodeGen::DoModByPowerOf2I(LModByPowerOf2I* instr) {
 }
 
 
-void LCodeGen::DoModByConstI(LModByConstI* instr) {
-  Register dividend = ToRegister(instr->dividend());
-  int32_t divisor = instr->divisor();
-  Register result = ToRegister(instr->result());
-  ASSERT(!dividend.is(result));
-
-  if (divisor == 0) {
-    DeoptimizeIf(al, instr->environment());
-    return;
-  }
-
-  __ FlooringDiv(result, dividend, Abs(divisor));
-  __ mov(ip, Operand(Abs(divisor)));
-  __ smull(result, ip, result, ip);
-  __ sub(result, dividend, result, SetCC);
-
-  // Check for negative zero.
-  HMod* hmod = instr->hydrogen();
-  if (hmod->CheckFlag(HValue::kBailoutOnMinusZero) &&
-      hmod->left()->CanBeNegative()) {
-    Label remainder_not_zero;
-    __ b(ne, &remainder_not_zero);
-    __ cmp(dividend, Operand::Zero());
-    DeoptimizeIf(lt, instr->environment());
-    __ bind(&remainder_not_zero);
-  }
-}
-
-
 void LCodeGen::DoModI(LModI* instr) {
   HMod* hmod = instr->hydrogen();
   HValue* left = hmod->left();
@@ -1287,6 +1258,100 @@ void LCodeGen::DoModI(LModI* instr) {
 }
 
 
+void LCodeGen::EmitSignedIntegerDivisionByConstant(
+    Register result,
+    Register dividend,
+    int32_t divisor,
+    Register remainder,
+    Register scratch,
+    LEnvironment* environment) {
+  ASSERT(!AreAliased(dividend, scratch, ip));
+  ASSERT(LChunkBuilder::HasMagicNumberForDivisor(divisor));
+
+  uint32_t divisor_abs = abs(divisor);
+
+  int32_t power_of_2_factor =
+    CompilerIntrinsics::CountTrailingZeros(divisor_abs);
+
+  switch (divisor_abs) {
+    case 0:
+      DeoptimizeIf(al, environment);
+      return;
+
+    case 1:
+      if (divisor > 0) {
+        __ Move(result, dividend);
+      } else {
+        __ rsb(result, dividend, Operand::Zero(), SetCC);
+        DeoptimizeIf(vs, environment);
+      }
+      // Compute the remainder.
+      __ mov(remainder, Operand::Zero());
+      return;
+
+    default:
+      if (IsPowerOf2(divisor_abs)) {
+        // Branch and condition free code for integer division by a power
+        // of two.
+        int32_t power = WhichPowerOf2(divisor_abs);
+        if (power > 1) {
+          __ mov(scratch, Operand(dividend, ASR, power - 1));
+        }
+        __ add(scratch, dividend, Operand(scratch, LSR, 32 - power));
+        __ mov(result, Operand(scratch, ASR, power));
+        // Negate if necessary.
+        // We don't need to check for overflow because the case '-1' is
+        // handled separately.
+        if (divisor < 0) {
+          ASSERT(divisor != -1);
+          __ rsb(result, result, Operand::Zero());
+        }
+        // Compute the remainder.
+        if (divisor > 0) {
+          __ sub(remainder, dividend, Operand(result, LSL, power));
+        } else {
+          __ add(remainder, dividend, Operand(result, LSL, power));
+        }
+        return;
+      } else {
+        // Use magic numbers for a few specific divisors.
+        // Details and proofs can be found in:
+        // - Hacker's Delight, Henry S. Warren, Jr.
+        // - The PowerPC Compiler Writer’s Guide
+        // and probably many others.
+        //
+        // We handle
+        //   <divisor with magic numbers> * <power of 2>
+        // but not
+        //   <divisor with magic numbers> * <other divisor with magic numbers>
+        DivMagicNumbers magic_numbers =
+          DivMagicNumberFor(divisor_abs >> power_of_2_factor);
+        // Branch and condition free code for integer division by a power
+        // of two.
+        const int32_t M = magic_numbers.M;
+        const int32_t s = magic_numbers.s + power_of_2_factor;
+
+        __ mov(ip, Operand(M));
+        __ smull(ip, scratch, dividend, ip);
+        if (M < 0) {
+          __ add(scratch, scratch, Operand(dividend));
+        }
+        if (s > 0) {
+          __ mov(scratch, Operand(scratch, ASR, s));
+        }
+        __ add(result, scratch, Operand(dividend, LSR, 31));
+        if (divisor < 0) __ rsb(result, result, Operand::Zero());
+        // Compute the remainder.
+        __ mov(ip, Operand(divisor));
+        // This sequence could be replaced with 'mls' when
+        // it gets implemented.
+        __ mul(scratch, result, ip);
+        __ sub(remainder, dividend, scratch);
+      }
+  }
+}
+
+
 void LCodeGen::DoDivByPowerOf2I(LDivByPowerOf2I* instr) {
   Register dividend = ToRegister(instr->dividend());
   int32_t divisor = instr->divisor();
@@ -1333,37 +1398,6 @@ void LCodeGen::DoDivByPowerOf2I(LDivByPowerOf2I* instr) {
 }
 
 
-void LCodeGen::DoDivByConstI(LDivByConstI* instr) {
-  Register dividend = ToRegister(instr->dividend());
-  int32_t divisor = instr->divisor();
-  Register result = ToRegister(instr->result());
-  ASSERT(!dividend.is(result));
-
-  if (divisor == 0) {
-    DeoptimizeIf(al, instr->environment());
-    return;
-  }
-
-  // Check for (0 / -x) that will produce negative zero.
-  HDiv* hdiv = instr->hydrogen();
-  if (hdiv->CheckFlag(HValue::kBailoutOnMinusZero) &&
-      hdiv->left()->RangeCanInclude(0) && divisor < 0) {
-    __ cmp(dividend, Operand::Zero());
-    DeoptimizeIf(eq, instr->environment());
-  }
-
-  __ FlooringDiv(result, dividend, Abs(divisor));
-  if (divisor < 0) __ rsb(result, result, Operand::Zero());
-
-  if (!hdiv->CheckFlag(HInstruction::kAllUsesTruncatingToInt32)) {
-    __ mov(ip, Operand(divisor));
-    __ smull(scratch0(), ip, result, ip);
-    __ sub(scratch0(), scratch0(), dividend, SetCC);
-    DeoptimizeIf(ne, instr->environment());
-  }
-}
-
-
 void LCodeGen::DoDivI(LDivI* instr) {
   const Register left = ToRegister(instr->left());
   const Register right = ToRegister(instr->right());
@@ -1497,25 +1531,71 @@ void LCodeGen::DoFlooringDivByPowerOf2I(LFlooringDivByPowerOf2I* instr) {
 
 
 void LCodeGen::DoFlooringDivByConstI(LFlooringDivByConstI* instr) {
-  Register dividend = ToRegister(instr->dividend());
-  int32_t divisor = instr->divisor();
+  Register left = ToRegister(instr->dividend());
+  Register remainder = ToRegister(instr->temp());
+  Register scratch = scratch0();
   Register result = ToRegister(instr->result());
-  ASSERT(!dividend.is(result));
 
-  if (divisor == 0) {
-    DeoptimizeIf(al, instr->environment());
-    return;
-  }
+  if (!CpuFeatures::IsSupported(SUDIV)) {
+    // If the CPU doesn't support sdiv instruction, we only optimize when we
+    // have magic numbers for the divisor. The standard integer division routine
+    // is usually slower than transitionning to VFP.
+    ASSERT(instr->divisor()->IsConstantOperand());
+    int32_t divisor = ToInteger32(LConstantOperand::cast(instr->divisor()));
+    ASSERT(LChunkBuilder::HasMagicNumberForDivisor(divisor));
+    if (divisor < 0) {
+      __ cmp(left, Operand::Zero());
+      DeoptimizeIf(eq, instr->environment());
+    }
+    EmitSignedIntegerDivisionByConstant(result,
+                                        left,
+                                        divisor,
+                                        remainder,
+                                        scratch,
+                                        instr->environment());
+    // We performed a truncating division. Correct the result if necessary.
+    __ cmp(remainder, Operand::Zero());
+    __ teq(remainder, Operand(divisor), ne);
+    __ sub(result, result, Operand(1), LeaveCC, mi);
+  } else {
+    CpuFeatureScope scope(masm(), SUDIV);
+    // TODO(svenpanne) We *statically* know the divisor, use that fact!
+    Register right = ToRegister(instr->divisor());
 
-  // Check for (0 / -x) that will produce negative zero.
-  HMathFloorOfDiv* hdiv = instr->hydrogen();
-  if (hdiv->CheckFlag(HValue::kBailoutOnMinusZero) &&
-      hdiv->left()->RangeCanInclude(0) && divisor < 0) {
-    __ cmp(dividend, Operand::Zero());
+    // Check for x / 0.
+    __ cmp(right, Operand::Zero());
     DeoptimizeIf(eq, instr->environment());
-  }
 
-  __ FlooringDiv(result, dividend, divisor);
+    // Check for (kMinInt / -1).
+    if (instr->hydrogen()->CheckFlag(HValue::kCanOverflow)) {
+      __ cmp(left, Operand(kMinInt));
+      __ cmp(right, Operand(-1), eq);
+      DeoptimizeIf(eq, instr->environment());
+    }
+
+    // Check for (0 / -x) that will produce negative zero.
+    if (instr->hydrogen()->CheckFlag(HValue::kBailoutOnMinusZero)) {
+      __ cmp(right, Operand::Zero());
+      __ cmp(left, Operand::Zero(), mi);
+      // "right" can't be null because the code would have already been
+      // deoptimized. The Z flag is set only if (right < 0) and (left == 0).
+      // In this case we need to deoptimize to produce a -0.
+      DeoptimizeIf(eq, instr->environment());
+    }
+
+    Label done;
+    __ sdiv(result, left, right);
+    // If both operands have the same sign then we are done.
+    __ eor(remainder, left, Operand(right), SetCC);
+    __ b(pl, &done);
+
+    // Check if the result needs to be corrected.
+    __ mls(remainder, result, right, left);
+    __ cmp(remainder, Operand::Zero());
+    __ sub(result, result, Operand(1), LeaveCC, ne);
+
+    __ bind(&done);
+  }
 }