Changeset 173205 in webkit

Timestamp:

Sep 3, 2014 7:15:09 AM (10 years ago)

Author:

commit-queue@webkit.org

Message:

Don't generate superfluous mov instructions for move immediate on ARM64.
​https://bugs.webkit.org/show_bug.cgi?id=136435

Patch by Akos Kiss <​akiss@inf.u-szeged.hu> on 2014-09-03
Reviewed by Michael Saboff.

On ARM64, the size of an immediate operand for a mov instruction is 16
bits. Thus, a move immediate offlineasm instruction may potentially be
split up to several machine level instructions. The current
implementation always emits a mov for the least significant 16 bits of
the value. However, if any of the bits 63:16 are significant then the
first emitted mov already filled bits 15:0 with zeroes (or ones, for
negative values). So, if bits 15:0 of the value are all zeroes (or ones)
then the last mov does not need to be emitted.

• offlineasm/arm64.rb:

Location:

trunk/Source/JavaScriptCore

Files:

• ChangeLog (modified) (1 diff)
• offlineasm/arm64.rb (modified) (1 diff)

trunk/Source/JavaScriptCore/ChangeLog

@@ +1 @@
+2014-09-03  Akos Kiss  <akiss@inf.u-szeged.hu>
+
+        Don't generate superfluous mov instructions for move immediate on ARM64.
+        https://bugs.webkit.org/show_bug.cgi?id=136435
+
+        Reviewed by Michael Saboff.
+
+        On ARM64, the size of an immediate operand for a mov instruction is 16
+        bits. Thus, a move immediate offlineasm instruction may potentially be
+        split up to several machine level instructions. The current
+        implementation always emits a mov for the least significant 16 bits of
+        the value. However, if any of the bits 63:16 are significant then the
+        first emitted mov already filled bits 15:0 with zeroes (or ones, for
+        negative values). So, if bits 15:0 of the value are all zeroes (or ones)
+        then the last mov does not need to be emitted.
+
+        * offlineasm/arm64.rb:
+
 2014-09-02  Brian J. Burg  <burg@cs.washington.edu>
 

trunk/Source/JavaScriptCore/offlineasm/arm64.rb

@@ -370 +370 @@
         | shift |
         currentValue = (value >> shift) & 0xffff
-        next if currentValue == (isNegative ? 0xffff : 0) and shift != 0
+        next if currentValue == (isNegative ? 0xffff : 0) and (shift != 0 or !first)
         if first
             if isNegative