Title: [196011] trunk/Websites/webkit.org
- Revision
- 196011
- Author
- [email protected]
- Date
- 2016-02-02 08:58:41 -0800 (Tue, 02 Feb 2016)
Log Message
Minor fixes for B3 IR documentation
https://bugs.webkit.org/show_bug.cgi?id=153782
Reviewed by Michael Saboff.
Fix minor issues that Geoff found.
* docs/b3/intermediate-representation.html:
Modified Paths
Diff
Modified: trunk/Websites/webkit.org/ChangeLog (196010 => 196011)
--- trunk/Websites/webkit.org/ChangeLog 2016-02-02 16:38:02 UTC (rev 196010)
+++ trunk/Websites/webkit.org/ChangeLog 2016-02-02 16:58:41 UTC (rev 196011)
@@ -1,3 +1,14 @@
+2016-02-02 Filip Pizlo <[email protected]>
+
+ Minor fixes for B3 IR documentation
+ https://bugs.webkit.org/show_bug.cgi?id=153782
+
+ Reviewed by Michael Saboff.
+
+ Fix minor issues that Geoff found.
+
+ * docs/b3/intermediate-representation.html:
+
2016-01-30 Filip Pizlo <[email protected]>
B3 documentation style shouldn't have hacks for h1
Modified: trunk/Websites/webkit.org/docs/b3/intermediate-representation.html (196010 => 196011)
--- trunk/Websites/webkit.org/docs/b3/intermediate-representation.html 2016-02-02 16:38:02 UTC (rev 196010)
+++ trunk/Websites/webkit.org/docs/b3/intermediate-representation.html 2016-02-02 16:58:41 UTC (rev 196011)
@@ -88,13 +88,19 @@
<h2>Stack Slot</h2>
<p>B3 exposes the concept of stack-allocated data and gives the client a lot of control.
- You can force stack slots to end up at a particular offset from the frame pointer, though
- this is very dangerous. After compilation is done, you can get the selected frame pointer
- offset from any stack slot. Usually, you let B3 select where stack slots go, and then use
- the StackSlot API to get its FP offset after compilation.</p>
+ By default, stack slots get allocated wherever B3 chooses. It will try to pack them as
+ much as possible. After compilation is done, you can retrieve each stack slot's location
+ in the form of an offset from the frame pointer.</p>
+ <p>You can force stack slots to end up at a particular offset from the frame pointer, though
+ this is very dangerous. For example, B3 assumes that it can use the slots closest to the
+ frame pointer for callee-saves, and currently when you force something to a particular
+ frame pointer offset, there is no mechanism to notice that this space is also being used
+ for callee-saves. Therefore, we recommend not using the frame pointer offset forcing
+ feature unless you know a lot about the ABI and you have no other choice.</p>
+
<p>Stack slots are also used for creating non-SSA variables with the intention of having B3
- convert them into SSA. There are two kinds of stack lots.</p>
+ convert them into SSA. There are two kinds of stack slots.</p>
<dl>
<dt>Anonymous</dt>
@@ -118,7 +124,8 @@
predecessors. Each basic block may have zero or more successors. The successors are
controlled by the basic block's last Value, which must be a ControlValue instance.</p>
- <p>Each basic block contains a Vector<Value*> as the contents of the block.</p>
+ <p>Each basic block contains a Vector<Value*> as the contents of the block. Control
+ flow inside the block is implicit based on the order of Values in the vector.</p>
<h2>Opcodes</h2>
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