Changeset 69743 in webkit for trunk/JavaScriptCore/assembler/LinkBuffer.h

Timestamp:

Oct 13, 2010, 11:45:26 PM (15 years ago)

Author:

[email protected]

Message:

2010-10-13 David Goodwin <​[email protected]>

Reviewed by Oliver Hunt.

ARMv7 JIT should generated conditional branches when possible
​https://bugs.webkit.org/show_bug.cgi?id=47384

Use different jump padding sizes for conditional and unconditional
jumps (12 bytes and 10 bytes respectively). This allows the JIT to
include the IT instruction as part of the conditional jump sequence
which in turn allows it to optimize away the IT using an ARMv7
conditional branch instruction. Use 2-byte B(T1) and 4-byte B(T3) for
conditional branches when displacement is in range. Also use IT/B(T4)
for conditional branch when displacement does not fit in B(T3).

For unconditional jump, instruction selection options are:
B(T2), B(T4), MOVW/MOVT/BX. For conditional jump, instruction selection
options are: B(T1), B(T3), IT/B(T4), ITTT/MOVW/MOVT/BX.

• assembler/ARMv7Assembler.cpp:
• assembler/ARMv7Assembler.h: (JSC::ARMv7Assembler::JmpSrc::JmpSrc): (JSC::ARMv7Assembler::ifThenElse): (JSC::ARMv7Assembler::jumpSizeDelta): (JSC::ARMv7Assembler::canCompact): (JSC::ARMv7Assembler::computeJumpType): (JSC::ARMv7Assembler::link): (JSC::ARMv7Assembler::canBeJumpT1): (JSC::ARMv7Assembler::canBeJumpT3): (JSC::ARMv7Assembler::canBeJumpT4): (JSC::ARMv7Assembler::linkJumpT1): (JSC::ARMv7Assembler::linkJumpT3): (JSC::ARMv7Assembler::linkJumpT4): (JSC::ARMv7Assembler::linkConditionalJumpT4): (JSC::ARMv7Assembler::linkBX): (JSC::ARMv7Assembler::linkConditionalBX): (JSC::ARMv7Assembler::linkJumpAbsolute):
• assembler/LinkBuffer.h: (JSC::LinkBuffer::linkCode):
• assembler/MacroAssemblerARMv7.h: (JSC::MacroAssemblerARMv7::canCompact): (JSC::MacroAssemblerARMv7::computeJumpType): (JSC::MacroAssemblerARMv7::jumpSizeDelta): (JSC::MacroAssemblerARMv7::jump): (JSC::MacroAssemblerARMv7::nearCall): (JSC::MacroAssemblerARMv7::call): (JSC::MacroAssemblerARMv7::ret): (JSC::MacroAssemblerARMv7::tailRecursiveCall): (JSC::MacroAssemblerARMv7::makeJump): (JSC::MacroAssemblerARMv7::makeBranch):

File:

• trunk/JavaScriptCore/assembler/LinkBuffer.h (modified) (2 diffs)

trunk/JavaScriptCore/assembler/LinkBuffer.h

@@ -1 +1 @@
 /*
- * Copyright (C) 2009 Apple Inc. All rights reserved.
+ * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -236 +236 @@
             
             JumpLinkType jumpLinkType = m_assembler->computeJumpType(jumpsToLink[i], linkBase + writePtr, target);
-
-            // Step back in the write stream
-            int32_t delta = m_assembler->jumpSizeDelta(jumpLinkType);
-            if (delta) {
-                writePtr -= delta;
-                m_assembler->recordLinkOffsets(jumpsToLink[i].from() - delta, readPtr, readPtr - writePtr);
+            // Compact branch if we can...
+            if (m_assembler->canCompact(jumpsToLink[i].type())) {
+                // Step back in the write stream
+                int32_t delta = m_assembler->jumpSizeDelta(jumpsToLink[i].type(), jumpLinkType);
+                if (delta) {
+                    writePtr -= delta;
+                    m_assembler->recordLinkOffsets(jumpsToLink[i].from() - delta, readPtr, readPtr - writePtr);
+                }
             }
             jumpsToLink[i].setFrom(writePtr);