[arm64] Fix pre-shifted immediate generation involving csp.

src/arm64/macro-assembler-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/arm64/frames-arm64.h"
 #include "src/assembler.h"
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
@@ skipping 111 matching lines @@
       }
     }
 
     unsigned n, imm_s, imm_r;
     if (IsImmLogical(immediate, reg_size, &n, &imm_s, &imm_r)) {
       // Immediate can be encoded in the instruction.
       LogicalImmediate(rd, rn, n, imm_s, imm_r, op);
     } else {
       // Immediate can't be encoded: synthesize using move immediate.
       Register temp = temps.AcquireSameSizeAs(rn);
-      Operand imm_operand = MoveImmediateForShiftedOp(temp, immediate);
+
+      // If the left-hand input is the stack pointer, we can't pre-shift the
+      // immediate, as the encoding won't allow the subsequent post shift.
+      PreShiftImmMode mode = rn.Is(csp) ? kNoShift : kAnyShift;
+      Operand imm_operand = MoveImmediateForShiftedOp(temp, immediate, mode);
+
       if (rd.Is(csp)) {
         // If rd is the stack pointer we cannot use it as the destination
         // register so we use the temp register as an intermediate again.
         Logical(temp, rn, imm_operand, op);
         Mov(csp, temp);
         AssertStackConsistency();
       } else {
         Logical(rd, rn, imm_operand, op);
       }
     }
@@ skipping 452 matching lines @@
     movn(dst, dst.Is64Bits() ? ~imm : (~imm & kWRegMask));
     return true;
   } else if (IsImmLogical(imm, reg_size, &n, &imm_s, &imm_r)) {
     // Immediate can be represented in a logical orr instruction.
     LogicalImmediate(dst, AppropriateZeroRegFor(dst), n, imm_s, imm_r, ORR);
     return true;
   }
   return false;
 }
 
-
 Operand MacroAssembler::MoveImmediateForShiftedOp(const Register& dst,
-                                                  int64_t imm) {
+                                                  int64_t imm,
+                                                  PreShiftImmMode mode) {
   int reg_size = dst.SizeInBits();
 
   // Encode the immediate in a single move instruction, if possible.
   if (TryOneInstrMoveImmediate(dst, imm)) {
     // The move was successful; nothing to do here.
   } else {
     // Pre-shift the immediate to the least-significant bits of the register.
     int shift_low = CountTrailingZeros(imm, reg_size);
+    if (mode == kLimitShiftForSP) {
+      // When applied to the stack pointer, the subsequent arithmetic operation
+      // can use the extend form to shift left by a maximum of four bits. Right
+      // shifts are not allowed, so we filter them out later before the new
+      // immediate is tested.
+      shift_low = std::min(shift_low, 4);
+    }
     int64_t imm_low = imm >> shift_low;
 
     // Pre-shift the immediate to the most-significant bits of the register. We
     // insert set bits in the least-significant bits, as this creates a
     // different immediate that may be encodable using movn or orr-immediate.
     // If this new immediate is encodable, the set bits will be eliminated by
     // the post shift on the following instruction.
     int shift_high = CountLeadingZeros(imm, reg_size);
     int64_t imm_high = (imm << shift_high) | ((1 << shift_high) - 1);
 
-    if (TryOneInstrMoveImmediate(dst, imm_low)) {
+    if ((mode != kNoShift) && TryOneInstrMoveImmediate(dst, imm_low)) {
       // The new immediate has been moved into the destination's low bits:
       // return a new leftward-shifting operand.
       return Operand(dst, LSL, shift_low);
-    } else if (TryOneInstrMoveImmediate(dst, imm_high)) {
+    } else if ((mode == kAnyShift) && TryOneInstrMoveImmediate(dst, imm_high)) {
       // The new immediate has been moved into the destination's high bits:
       // return a new rightward-shifting operand.
       return Operand(dst, LSR, shift_high);
     } else {
       // Use the generic move operation to set up the immediate.
       Mov(dst, imm);
     }
   }
   return Operand(dst);
 }
@@ skipping 15 matching lines @@
     Register temp = temps.AcquireX();
     Ldr(temp, operand.immediate());
     AddSubMacro(rd, rn, temp, S, op);
   } else if ((operand.IsImmediate() &&
               !IsImmAddSub(operand.ImmediateValue()))      ||
              (rn.IsZero() && !operand.IsShiftedRegister()) ||
              (operand.IsShiftedRegister() && (operand.shift() == ROR))) {
     UseScratchRegisterScope temps(this);
     Register temp = temps.AcquireSameSizeAs(rn);
     if (operand.IsImmediate()) {
+      PreShiftImmMode mode = kAnyShift;
+
+      // If the destination or source register is the stack pointer, we can
+      // only pre-shift the immediate right by values supported in the add/sub
+      // extend encoding.
+      if (rd.Is(csp)) {
+        // If the destination is SP and flags will be set, we can't pre-shift
+        // the immediate at all.
+        mode = (S == SetFlags) ? kNoShift : kLimitShiftForSP;
+      } else if (rn.Is(csp)) {
+        mode = kLimitShiftForSP;
+      }
+
       Operand imm_operand =
-          MoveImmediateForShiftedOp(temp, operand.ImmediateValue());
+          MoveImmediateForShiftedOp(temp, operand.ImmediateValue(), mode);
       AddSub(rd, rn, imm_operand, S, op);
     } else {
       Mov(temp, operand);
       AddSub(rd, rn, temp, S, op);
     }
   } else {
     AddSub(rd, rn, operand, S, op);
   }
 }
 
@@ skipping 4091 matching lines @@
 }
 
 
 #undef __
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM64