X64 implementation: if-then-else

src/x64/jump-target-x64.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
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 //       with the distribution.
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 //       from this software without specific prior written permission.
 //
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 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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+#include "v8.h"
+
+#include "codegen-inl.h"
+#include "jump-target-inl.h"
+#include "register-allocator-inl.h"
+
+namespace v8 {
+namespace internal {
+
+// -------------------------------------------------------------------------
+// JumpTarget implementation.
+
+#define __ ACCESS_MASM(cgen()->masm())
+
+void JumpTarget::DoJump() {
+  ASSERT(cgen()->has_valid_frame());
+  // Live non-frame registers are not allowed at unconditional jumps
+  // because we have no way of invalidating the corresponding results
+  // which are still live in the C++ code.
+  ASSERT(cgen()->HasValidEntryRegisters());
+
+  if (is_bound()) {
+    // Backward jump.  There is an expected frame to merge to.
+    ASSERT(direction_ == BIDIRECTIONAL);
+    cgen()->frame()->PrepareMergeTo(entry_frame_);
+    cgen()->frame()->MergeTo(entry_frame_);
+    cgen()->DeleteFrame();
+    __ jmp(&entry_label_);
+  } else if (entry_frame_ != NULL) {
+    // Forward jump with a preconfigured entry frame.  Assert the
+    // current frame matches the expected one and jump to the block.
+    ASSERT(cgen()->frame()->Equals(entry_frame_));
+    cgen()->DeleteFrame();
+    __ jmp(&entry_label_);
+  } else {
+    // Forward jump.  Remember the current frame and emit a jump to
+    // its merge code.
+    AddReachingFrame(cgen()->frame());
+    RegisterFile empty;
+    cgen()->SetFrame(NULL, &empty);
+    __ jmp(&merge_labels_.last());
+  }
+}
+
+
+void JumpTarget::DoBranch(Condition cc, Hint b) {
+  ASSERT(cgen() != NULL);
+  ASSERT(cgen()->has_valid_frame());
+
+  if (is_bound()) {
+    ASSERT(direction_ == BIDIRECTIONAL);
+    // Backward branch.  We have an expected frame to merge to on the
+    // backward edge.
+
+    // Swap the current frame for a copy (we do the swapping to get
+    // the off-frame registers off the fall through) to use for the
+    // branch.
+    VirtualFrame* fall_through_frame = cgen()->frame();
+    VirtualFrame* branch_frame = new VirtualFrame(fall_through_frame);
+    RegisterFile non_frame_registers;
+    cgen()->SetFrame(branch_frame, &non_frame_registers);
+
+    // Check if we can avoid merge code.
+    cgen()->frame()->PrepareMergeTo(entry_frame_);
+    if (cgen()->frame()->Equals(entry_frame_)) {
+      // Branch right in to the block.
+      cgen()->DeleteFrame();
+      __ j(cc, &entry_label_);
+      cgen()->SetFrame(fall_through_frame, &non_frame_registers);
+      return;
+    }
+
+    // Check if we can reuse existing merge code.
+    for (int i = 0; i < reaching_frames_.length(); i++) {
+      if (reaching_frames_[i] != NULL &&
+          cgen()->frame()->Equals(reaching_frames_[i])) {
+        // Branch to the merge code.
+        cgen()->DeleteFrame();
+        __ j(cc, &merge_labels_[i]);
+        cgen()->SetFrame(fall_through_frame, &non_frame_registers);
+        return;
+      }
+    }
+
+    // To emit the merge code here, we negate the condition and branch
+    // around the merge code on the fall through path.
+    Label original_fall_through;
+    __ j(NegateCondition(cc), &original_fall_through);
+    cgen()->frame()->MergeTo(entry_frame_);
+    cgen()->DeleteFrame();
+    __ jmp(&entry_label_);
+    cgen()->SetFrame(fall_through_frame, &non_frame_registers);
+    __ bind(&original_fall_through);
+
+  } else if (entry_frame_ != NULL) {
+    // Forward branch with a preconfigured entry frame.  Assert the
+    // current frame matches the expected one and branch to the block.
+    ASSERT(cgen()->frame()->Equals(entry_frame_));
+    // Explicitly use the macro assembler instead of __ as forward
+    // branches are expected to be a fixed size (no inserted
+    // coverage-checking instructions please).  This is used in
+    // Reference::GetValue.
+    cgen()->masm()->j(cc, &entry_label_);
+
+  } else {
+    // Forward branch.  A copy of the current frame is remembered and
+    // a branch to the merge code is emitted.  Explicitly use the
+    // macro assembler instead of __ as forward branches are expected
+    // to be a fixed size (no inserted coverage-checking instructions
+    // please).  This is used in Reference::GetValue.
+    AddReachingFrame(new VirtualFrame(cgen()->frame()));
+    cgen()->masm()->j(cc, &merge_labels_.last());
+  }
+}
+
+
+void JumpTarget::Call() {
+  // Call is used to push the address of the catch block on the stack as
+  // a return address when compiling try/catch and try/finally.  We
+  // fully spill the frame before making the call.  The expected frame
+  // at the label (which should be the only one) is the spilled current
+  // frame plus an in-memory return address.  The "fall-through" frame
+  // at the return site is the spilled current frame.
+  ASSERT(cgen() != NULL);
+  ASSERT(cgen()->has_valid_frame());
+  // There are no non-frame references across the call.
+  ASSERT(cgen()->HasValidEntryRegisters());
+  ASSERT(!is_linked());
+
+  cgen()->frame()->SpillAll();
+  VirtualFrame* target_frame = new VirtualFrame(cgen()->frame());
+  target_frame->Adjust(1);
+  // We do not expect a call with a preconfigured entry frame.
+  ASSERT(entry_frame_ == NULL);
+  AddReachingFrame(target_frame);
+  __ call(&merge_labels_.last());
+}
+
+
+void JumpTarget::DoBind() {
+  ASSERT(cgen() != NULL);
+  ASSERT(!is_bound());
+
+  // Live non-frame registers are not allowed at the start of a basic
+  // block.
+  ASSERT(!cgen()->has_valid_frame() || cgen()->HasValidEntryRegisters());
+
+  // Fast case: the jump target was manually configured with an entry
+  // frame to use.
+  if (entry_frame_ != NULL) {
+    // Assert no reaching frames to deal with.
+    ASSERT(reaching_frames_.is_empty());
+    ASSERT(!cgen()->has_valid_frame());
+
+    RegisterFile empty;
+    if (direction_ == BIDIRECTIONAL) {
+      // Copy the entry frame so the original can be used for a
+      // possible backward jump.
+      cgen()->SetFrame(new VirtualFrame(entry_frame_), &empty);
+    } else {
+      // Take ownership of the entry frame.
+      cgen()->SetFrame(entry_frame_, &empty);
+      entry_frame_ = NULL;
+    }
+    __ bind(&entry_label_);
+    return;
+  }
+
+  if (!is_linked()) {
+    ASSERT(cgen()->has_valid_frame());
+    if (direction_ == FORWARD_ONLY) {
+      // Fast case: no forward jumps and no possible backward jumps.
+      // The stack pointer can be floating above the top of the
+      // virtual frame before the bind.  Afterward, it should not.
+      VirtualFrame* frame = cgen()->frame();
+      int difference = frame->stack_pointer_ - (frame->element_count() - 1);
+      if (difference > 0) {
+        frame->stack_pointer_ -= difference;
+        __ addq(rsp, Immediate(difference * kPointerSize));
+      }
+    } else {
+      ASSERT(direction_ == BIDIRECTIONAL);
+      // Fast case: no forward jumps, possible backward ones.  Remove
+      // constants and copies above the watermark on the fall-through
+      // frame and use it as the entry frame.
+      cgen()->frame()->MakeMergable();
+      entry_frame_ = new VirtualFrame(cgen()->frame());
+    }
+    __ bind(&entry_label_);
+    return;
+  }
+
+  if (direction_ == FORWARD_ONLY &&
+      !cgen()->has_valid_frame() &&
+      reaching_frames_.length() == 1) {
+    // Fast case: no fall-through, a single forward jump, and no
+    // possible backward jumps.  Pick up the only reaching frame, take
+    // ownership of it, and use it for the block about to be emitted.
+    VirtualFrame* frame = reaching_frames_[0];
+    RegisterFile empty;
+    cgen()->SetFrame(frame, &empty);
+    reaching_frames_[0] = NULL;
+    __ bind(&merge_labels_[0]);
+
+    // The stack pointer can be floating above the top of the
+    // virtual frame before the bind.  Afterward, it should not.
+    int difference = frame->stack_pointer_ - (frame->element_count() - 1);
+    if (difference > 0) {
+      frame->stack_pointer_ -= difference;
+      __ addq(rsp, Immediate(difference * kPointerSize));
+    }
+
+    __ bind(&entry_label_);
+    return;
+  }
+
+  // If there is a current frame, record it as the fall-through.  It
+  // is owned by the reaching frames for now.
+  bool had_fall_through = false;
+  if (cgen()->has_valid_frame()) {
+    had_fall_through = true;
+    AddReachingFrame(cgen()->frame());  // Return value ignored.
+    RegisterFile empty;
+    cgen()->SetFrame(NULL, &empty);
+  }
+
+  // Compute the frame to use for entry to the block.
+  ComputeEntryFrame();
+
+  // Some moves required to merge to an expected frame require purely
+  // frame state changes, and do not require any code generation.
+  // Perform those first to increase the possibility of finding equal
+  // frames below.
+  for (int i = 0; i < reaching_frames_.length(); i++) {
+    if (reaching_frames_[i] != NULL) {
+      reaching_frames_[i]->PrepareMergeTo(entry_frame_);
+    }
+  }
+
+  if (is_linked()) {
+    // There were forward jumps.  Handle merging the reaching frames
+    // to the entry frame.
+
+    // Loop over the (non-null) reaching frames and process any that
+    // need merge code.  Iterate backwards through the list to handle
+    // the fall-through frame first.  Set frames that will be
+    // processed after 'i' to NULL if we want to avoid processing
+    // them.
+    for (int i = reaching_frames_.length() - 1; i >= 0; i--) {
+      VirtualFrame* frame = reaching_frames_[i];
+
+      if (frame != NULL) {
+        // Does the frame (probably) need merge code?
+        if (!frame->Equals(entry_frame_)) {
+          // We could have a valid frame as the fall through to the
+          // binding site or as the fall through from a previous merge
+          // code block.  Jump around the code we are about to
+          // generate.
+          if (cgen()->has_valid_frame()) {
+            cgen()->DeleteFrame();
+            __ jmp(&entry_label_);
+          }
+          // Pick up the frame for this block.  Assume ownership if
+          // there cannot be backward jumps.
+          RegisterFile empty;
+          if (direction_ == BIDIRECTIONAL) {
+            cgen()->SetFrame(new VirtualFrame(frame), &empty);
+          } else {
+            cgen()->SetFrame(frame, &empty);
+            reaching_frames_[i] = NULL;
+          }
+          __ bind(&merge_labels_[i]);
+
+          // Loop over the remaining (non-null) reaching frames,
+          // looking for any that can share merge code with this one.
+          for (int j = 0; j < i; j++) {
+            VirtualFrame* other = reaching_frames_[j];
+            if (other != NULL && other->Equals(cgen()->frame())) {
+              // Set the reaching frame element to null to avoid
+              // processing it later, and then bind its entry label.
+              reaching_frames_[j] = NULL;
+              __ bind(&merge_labels_[j]);
+            }
+          }
+
+          // Emit the merge code.
+          cgen()->frame()->MergeTo(entry_frame_);
+        } else if (i == reaching_frames_.length() - 1 && had_fall_through) {
+          // If this is the fall through frame, and it didn't need
+          // merge code, we need to pick up the frame so we can jump
+          // around subsequent merge blocks if necessary.
+          RegisterFile empty;
+          cgen()->SetFrame(frame, &empty);
+          reaching_frames_[i] = NULL;
+        }
+      }
+    }
+
+    // The code generator may not have a current frame if there was no
+    // fall through and none of the reaching frames needed merging.
+    // In that case, clone the entry frame as the current frame.
+    if (!cgen()->has_valid_frame()) {
+      RegisterFile empty;
+      cgen()->SetFrame(new VirtualFrame(entry_frame_), &empty);
+    }
+
+    // There may be unprocessed reaching frames that did not need
+    // merge code.  They will have unbound merge labels.  Bind their
+    // merge labels to be the same as the entry label and deallocate
+    // them.
+    for (int i = 0; i < reaching_frames_.length(); i++) {
+      if (!merge_labels_[i].is_bound()) {
+        reaching_frames_[i] = NULL;
+        __ bind(&merge_labels_[i]);
+      }
+    }
+
+    // There are non-NULL reaching frames with bound labels for each
+    // merge block, but only on backward targets.
+  } else {
+    // There were no forward jumps.  There must be a current frame and
+    // this must be a bidirectional target.
+    ASSERT(reaching_frames_.length() == 1);
+    ASSERT(reaching_frames_[0] != NULL);
+    ASSERT(direction_ == BIDIRECTIONAL);
+
+    // Use a copy of the reaching frame so the original can be saved
+    // for possible reuse as a backward merge block.
+    RegisterFile empty;
+    cgen()->SetFrame(new VirtualFrame(reaching_frames_[0]), &empty);
+    __ bind(&merge_labels_[0]);
+    cgen()->frame()->MergeTo(entry_frame_);
+  }
+
+  __ bind(&entry_label_);
+}
+
+#undef __
+
+
+} }  // namespace v8::internal