AuroraMiddleware/v8
1
0
Fork 0
Code Issues 2 Pull Requests Releases Wiki Activity

[turbofan] Improve lowering for NumberAbs to Int32Abs.

Browse Source 
We can compute the absolute integer value w/o any conditional execution
by using the bit trick formula

  let sign = input >> 31 in
  (input ^ sign) - sign

which generates fairly decent code on all supported architectures.

R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2169293002
Cr-Commit-Position: refs/heads/master@{#37965}
This commit is contained in:
bmeurer 2016-07-21 21:33:46 -07:00 committed by Commit bot
parent 7b5f56ca60
commit 085ec5c25f
1 changed files with 10 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
src/compiler/simplified-lowering.cc
View File

@ -3117,14 +3117,18 @@ Node* SimplifiedLowering::Float64Trunc(Node* const node) {
}
Node* SimplifiedLowering::Int32Abs(Node* const node) {
Node* const zero = jsgraph()->Int32Constant(0);
Node* const input = node->InputAt(0);
// if 0 < input then input else 0 - input
return graph()->NewNode(
common()->Select(MachineRepresentation::kWord32, BranchHint::kTrue),
graph()->NewNode(machine()->Int32LessThan(), zero, input), input,
graph()->NewNode(machine()->Int32Sub(), zero, input));
// Generate case for absolute integer value.
//
// let sign = input >> 31 in
// (input ^ sign) - sign
Node* sign = graph()->NewNode(machine()->Word32Sar(), input,
jsgraph()->Int32Constant(31));
return graph()->NewNode(machine()->Int32Sub(),
graph()->NewNode(machine()->Word32Xor(), input, sign),
sign);
}
Node* SimplifiedLowering::Int32Div(Node* const node) {