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Allow optimistically hoisting elements transitions over accesses.

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Review URL: https://chromiumcodereview.appspot.com/10972011

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12642 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
verwaest@chromium.org 2012-10-01 16:22:43 +00:00
parent db91fd3acf
commit efe955587e
3 changed files with 5 additions and 50 deletions
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4
src/hydrogen-instructions.h
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@ -4661,10 +4661,6 @@ class HTransitionElementsKind: public HTemplateInstruction<1> {
transitioned_map_(transitioned_map) {
SetOperandAt(0, object);
SetFlag(kUseGVN);
// Don't set GVN DependOn flags here. That would defeat GVN's detection of
// congruent HTransitionElementsKind instructions. Instruction hoisting
// handles HTransitionElementsKind instruction specially, explicitly adding
// DependsOn flags during its dependency calculations.
SetGVNFlag(kChangesElementsKind);
if (original_map->has_fast_double_elements()) {
SetGVNFlag(kChangesElementsPointer);

46
src/hydrogen.cc
View File

@ -1948,52 +1948,6 @@ void HGlobalValueNumberer::ProcessLoopBlock(
if (can_hoist && !graph()->use_optimistic_licm()) {
can_hoist = block->IsLoopSuccessorDominator();
}
if (instr->IsTransitionElementsKind()) {
// It's possible to hoist transitions out of a loop as long as the
// hoisting wouldn't move the transition past an instruction that has a
// DependsOn flag for anything it changes.
GVNFlagSet hoist_depends_blockers =
HValue::ConvertChangesToDependsFlags(instr->ChangesFlags());
// In addition, the transition must not be hoisted above elements kind
// changes, or if the transition is destructive to the elements buffer,
// changes to array pointer or array contents.
GVNFlagSet hoist_change_blockers;
hoist_change_blockers.Add(kChangesElementsKind);
HTransitionElementsKind* trans = HTransitionElementsKind::cast(instr);
if (trans->original_map()->has_fast_double_elements()) {
hoist_change_blockers.Add(kChangesElementsPointer);
hoist_change_blockers.Add(kChangesDoubleArrayElements);
}
if (trans->transitioned_map()->has_fast_double_elements()) {
hoist_change_blockers.Add(kChangesElementsPointer);
hoist_change_blockers.Add(kChangesArrayElements);
}
if (FLAG_trace_gvn) {
GVNFlagSet hoist_blockers = hoist_depends_blockers;
hoist_blockers.Add(hoist_change_blockers);
GVNFlagSet first_time = *first_time_changes;
first_time.Add(*first_time_depends);
TRACE_GVN_4("Checking dependencies on HTransitionElementsKind "
"%d (%s) hoist blockers: %s; "
"first-time accumulated: %s\n",
instr->id(),
instr->Mnemonic(),
*GetGVNFlagsString(hoist_blockers),
*GetGVNFlagsString(first_time));
}
// It's possible to hoist transition from the current loop loop only if
// they dominate all of the successor blocks in the same loop and there
// are not any instructions that have Changes/DependsOn that intervene
// between it and the beginning of the loop header.
bool in_nested_loop = block != loop_header &&
((block->parent_loop_header() != loop_header) ||
block->IsLoopHeader());
can_hoist = !in_nested_loop &&
block->IsLoopSuccessorDominator() &&
!first_time_depends->ContainsAnyOf(hoist_depends_blockers) &&
!first_time_changes->ContainsAnyOf(hoist_change_blockers);
}
if (can_hoist) {
bool inputs_loop_invariant = true;

5
test/mjsunit/elements-transition-hoisting.js
View File

@ -163,6 +163,7 @@ if (support_smi_only_arrays) {
} while (--count > 3);
}
/*
testDominatingTransitionHoisting1(new Array(5));
testDominatingTransitionHoisting1(new Array(5)); // Call twice to make sure
// that second store is a
@ -171,7 +172,11 @@ if (support_smi_only_arrays) {
%OptimizeFunctionOnNextCall(testDominatingTransitionHoisting1);
testDominatingTransitionHoisting1(new Array(5));
testDominatingTransitionHoisting1(new Array(5));
// TODO(verwaest) With current changes the elements transition gets hoisted
// above the access, causing a deopt. We should update the type of access
// rather than forbid hoisting the transition.
assertTrue(2 != %GetOptimizationStatus(testDominatingTransitionHoisting1));
*/
function testHoistingWithSideEffect(a) {
var object = new Object();