From 59f2b6c825774b07091e878611eba7d7738b633d Mon Sep 17 00:00:00 2001 From: "lrn@chromium.org" <lrn@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00> Date: Thu, 1 Jul 2010 13:19:32 +0000 Subject: [PATCH] X64: Made simpler version of fast-smi-loop code. It avoids the overflow check on the increment. Review URL: http://codereview.chromium.org/2835030 git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4998 ce2b1a6d-e550-0410-aec6-3dcde31c8c00 --- src/x64/codegen-x64.cc | 136 +++++++++++++++++++++++++++++++----- src/x64/codegen-x64.h | 3 + src/x64/virtual-frame-x64.h | 7 ++ 3 files changed, 129 insertions(+), 17 deletions(-) diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc index d58dd0226e..2c65dc74df 100644 --- a/src/x64/codegen-x64.cc +++ b/src/x64/codegen-x64.cc @@ -1600,11 +1600,130 @@ void CodeGenerator::SetTypeForStackSlot(Slot* slot, TypeInfo info) { } +void CodeGenerator::GenerateFastSmiLoop(ForStatement* node) { + // A fast smi loop is a for loop with an initializer + // that is a simple assignment of a smi to a stack variable, + // a test that is a simple test of that variable against a smi constant, + // and a step that is a increment/decrement of the variable, and + // where the variable isn't modified in the loop body. + // This guarantees that the variable is always a smi. + + Variable* loop_var = node->loop_variable(); + Smi* initial_value = *Handle<Smi>::cast(node->init() + ->StatementAsSimpleAssignment()->value()->AsLiteral()->handle()); + Smi* limit_value = *Handle<Smi>::cast( + node->cond()->AsCompareOperation()->right()->AsLiteral()->handle()); + Token::Value compare_op = + node->cond()->AsCompareOperation()->op(); + bool increments = + node->next()->StatementAsCountOperation()->op() == Token::INC; + + // Check that the condition isn't initially false. + bool initially_false = false; + int initial_int_value = initial_value->value(); + int limit_int_value = limit_value->value(); + switch (compare_op) { + case Token::LT: + initially_false = initial_int_value >= limit_int_value; + break; + case Token::LTE: + initially_false = initial_int_value > limit_int_value; + break; + case Token::GT: + initially_false = initial_int_value <= limit_int_value; + break; + case Token::GTE: + initially_false = initial_int_value < limit_int_value; + break; + default: + UNREACHABLE(); + } + if (initially_false) return; + + // Only check loop condition at the end. + + Visit(node->init()); + + JumpTarget loop(JumpTarget::BIDIRECTIONAL); + + IncrementLoopNesting(); + loop.Bind(); + + // Set number type of the loop variable to smi. + CheckStack(); // TODO(1222600): ignore if body contains calls. + + SetTypeForStackSlot(loop_var->slot(), TypeInfo::Smi()); + Visit(node->body()); + + if (node->continue_target()->is_linked()) { + node->continue_target()->Bind(); + } + + if (has_valid_frame()) { + CodeForStatementPosition(node); + Slot* loop_var_slot = loop_var->slot(); + if (loop_var_slot->type() == Slot::LOCAL) { + frame_->PushLocalAt(loop_var_slot->index()); + } else { + ASSERT(loop_var_slot->type() == Slot::PARAMETER); + frame_->PushParameterAt(loop_var_slot->index()); + } + Result loop_var_result = frame_->Pop(); + if (!loop_var_result.is_register()) { + loop_var_result.ToRegister(); + } + + if (increments) { + __ SmiAddConstant(loop_var_result.reg(), + loop_var_result.reg(), + Smi::FromInt(1)); + } else { + __ SmiSubConstant(loop_var_result.reg(), + loop_var_result.reg(), + Smi::FromInt(1)); + } + + { + __ SmiCompare(loop_var_result.reg(), limit_value); + Condition condition; + switch (compare_op) { + case Token::LT: + condition = less; + break; + case Token::LTE: + condition = less_equal; + break; + case Token::GT: + condition = greater; + break; + case Token::GTE: + condition = greater_equal; + break; + default: + condition = never; + UNREACHABLE(); + } + loop.Branch(condition); + } + loop_var_result.Unuse(); + } + if (node->break_target()->is_linked()) { + node->break_target()->Bind(); + } + DecrementLoopNesting(); +} + + void CodeGenerator::VisitForStatement(ForStatement* node) { ASSERT(!in_spilled_code()); Comment cmnt(masm_, "[ ForStatement"); CodeForStatementPosition(node); + if (node->is_fast_smi_loop()) { + GenerateFastSmiLoop(node); + return; + } + // Compile the init expression if present. if (node->init() != NULL) { Visit(node->init()); @@ -1694,16 +1813,6 @@ void CodeGenerator::VisitForStatement(ForStatement* node) { CheckStack(); // TODO(1222600): ignore if body contains calls. - // We know that the loop index is a smi if it is not modified in the - // loop body and it is checked against a constant limit in the loop - // condition. In this case, we reset the static type information of the - // loop index to smi before compiling the body, the update expression, and - // the bottom check of the loop condition. - if (node->is_fast_smi_loop()) { - // Set number type of the loop variable to smi. - SetTypeForStackSlot(node->loop_variable()->slot(), TypeInfo::Smi()); - } - Visit(node->body()); // If there is an update expression, compile it if necessary. @@ -1723,13 +1832,6 @@ void CodeGenerator::VisitForStatement(ForStatement* node) { } } - // Set the type of the loop variable to smi before compiling the test - // expression if we are in a fast smi loop condition. - if (node->is_fast_smi_loop() && has_valid_frame()) { - // Set number type of the loop variable to smi. - SetTypeForStackSlot(node->loop_variable()->slot(), TypeInfo::Smi()); - } - // Based on the condition analysis, compile the backward jump as // necessary. switch (info) { diff --git a/src/x64/codegen-x64.h b/src/x64/codegen-x64.h index cd03d2acc1..b9a3b70631 100644 --- a/src/x64/codegen-x64.h +++ b/src/x64/codegen-x64.h @@ -393,6 +393,9 @@ class CodeGenerator: public AstVisitor { // target (which can not be done more than once). void GenerateReturnSequence(Result* return_value); + // Generate code for a fast smi loop. + void GenerateFastSmiLoop(ForStatement* node); + // Returns the arguments allocation mode. ArgumentsAllocationMode ArgumentsMode(); diff --git a/src/x64/virtual-frame-x64.h b/src/x64/virtual-frame-x64.h index 0549e3cc2a..adf47e2167 100644 --- a/src/x64/virtual-frame-x64.h +++ b/src/x64/virtual-frame-x64.h @@ -388,6 +388,13 @@ class VirtualFrame : public ZoneObject { // Duplicate the top element of the frame. void Dup() { PushFrameSlotAt(element_count() - 1); } + // Duplicate the n'th element from the top of the frame. + // Dup(1) is equivalent to Dup(). + void Dup(int n) { + ASSERT(n > 0); + PushFrameSlotAt(element_count() - n); + } + // Pop an element from the top of the expression stack. Returns a // Result, which may be a constant or a register. Result Pop();