[llvm-commits] [llvm] r54708 - /llvm/trunk/lib/Target/X86/X86JITInfo.cpp

[Dale Johannesen]

Author: johannes
Date: Tue Aug 12 18:20:24 2008
New Revision: 54708

URL: http://llvm.org/viewvc/llvm-project?rev=54708&view=rev
Log:
When resolving a stub in x86-64 JIT, use a PC-relative branch
rather than the absolute address if the target is within range.


Modified:
    llvm/trunk/lib/Target/X86/X86JITInfo.cpp

Modified: llvm/trunk/lib/Target/X86/X86JITInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86JITInfo.cpp?rev=54708&r1=54707&r2=54708&view=diff

==============================================================================
--- llvm/trunk/lib/Target/X86/X86JITInfo.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86JITInfo.cpp Tue Aug 12 18:20:24 2008
@@ -352,7 +352,8 @@
   // Rewrite the call target... so that we don't end up here every time we
   // execute the call.
 #if defined (X86_64_JIT)
-  *(intptr_t *)(RetAddr - 0xa) = NewVal;
+  if (!isStub)
+    *(intptr_t *)(RetAddr - 0xa) = NewVal;
 #else
   *(intptr_t *)RetAddr = (intptr_t)(NewVal-RetAddr-4);
 #endif
@@ -363,7 +364,18 @@
     // when the requested function finally gets called.  This also makes the
     // 0xCD byte (interrupt) dead, so the marker doesn't effect anything.
 #if defined (X86_64_JIT)
-    ((unsigned char*)RetAddr)[0] = (2 | (4 << 3) | (3 << 6));
+    // If the target address is within 32-bit range of the stub, use a
+    // PC-relative branch instead of loading the actual address.  (This is
+    // considerably shorter than the 64-bit immediate load already there.)
+    // We assume here intptr_t is 64 bits.
+    intptr_t diff = NewVal-RetAddr+7;
+    if (diff >= -2147483648LL && diff <= 2147483647LL) {
+      *(unsigned char*)(RetAddr-0xc) = 0xE9;
+      *(intptr_t *)(RetAddr-0xb) = diff & 0xffffffff;
+    } else {
+      *(intptr_t *)(RetAddr - 0xa) = NewVal;
+      ((unsigned char*)RetAddr)[0] = (2 | (4 << 3) | (3 << 6));
+    }
 #else
     ((unsigned char*)RetAddr)[-1] = 0xE9;
 #endif