Changeset 237627 in webkit for trunk/Source/JavaScriptCore/offlineasm/x86.rb

Timestamp:

Oct 30, 2018, 11:14:04 PM (7 years ago)

Author:

[email protected]

Message:

[JSC][LLInt] Compact LLInt ASM code by removing unnecessary instructions
​https://bugs.webkit.org/show_bug.cgi?id=191092

Reviewed by Saam Barati.

Looking through LLIntAssembly.h, we can find several inefficiencies. This patch fixes the
following things to tighten LLInt ASM code.

1. Remove unnecessary load instructions. Use jmp with BaseIndex directly.
2. Introduce strength reduction for mul instructions in offlineasm layer. This is now critical

since mul instruction is executed in metadata operation in LLInt. If the given immediate is
a power of two, we convert it to lshift instruction.

• llint/LowLevelInterpreter32_64.asm:
• llint/LowLevelInterpreter64.asm:
• offlineasm/arm64.rb:
• offlineasm/instructions.rb:
• offlineasm/x86.rb:

File:

• trunk/Source/JavaScriptCore/offlineasm/x86.rb (modified) (1 diff)

trunk/Source/JavaScriptCore/offlineasm/x86.rb

@@ -799 +799 @@
         if operands.size == 3 and operands[0].is_a? Immediate
             $asm.puts "imul#{x86Suffix(kind)} #{x86Operands(kind, kind, kind)}"
-        else
-            # FIXME: could do some peephole in case the left operand is immediate and it's
-            # a power of two.
-            handleX86Op("imul#{x86Suffix(kind)}", kind)
-        end
+            return
+        end
+
+        if operands.size == 2 and operands[0].is_a? Immediate
+            imm = operands[0].value
+            if imm > 0 and isPowerOfTwo(imm)
+                $asm.puts "sal#{x86Suffix(kind)} #{orderOperands(Immediate.new(nil, Math.log2(imm).to_i).x86Operand(kind), operands[1].x86Operand(kind))}"
+                return
+            end
+        end
+
+        handleX86Op("imul#{x86Suffix(kind)}", kind)
     end