[llvm-commits] [llvm] r93393 - /llvm/trunk/lib/Target/ARM/ARMLoadStoreOptimizer.cpp

[Jakob Stoklund Olesen]

Author: stoklund
Date: Wed Jan 13 18:54:10 2010
New Revision: 93393

URL: http://llvm.org/viewvc/llvm-project?rev=93393&view=rev
Log:
Don't fold insufficiently aligned ldr/str into ldm/stm instructions.

An unaligned ldr causes a trap, and is then emulated by the kernel with
awesome performance. The darwin kernel does not emulate unaligned ldm/stm
Thumb2 instructions, so don't generate them.

This fixes the miscompilation of Multisource/Applications/JM/lencod for Thumb2.

Generating unaligned ldr/str pairs from a 16-bit aligned memcpy is probably
also a bad idea, but that is beyond the scope of this patch.

Modified:
    llvm/trunk/lib/Target/ARM/ARMLoadStoreOptimizer.cpp

Modified: llvm/trunk/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMLoadStoreOptimizer.cpp?rev=93393&r1=93392&r2=93393&view=diff

==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMLoadStoreOptimizer.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMLoadStoreOptimizer.cpp Wed Jan 13 18:54:10 2010
@@ -740,6 +740,18 @@
 /// isMemoryOp - Returns true if instruction is a memory operations (that this
 /// pass is capable of operating on).
 static bool isMemoryOp(const MachineInstr *MI) {
+  if (MI->hasOneMemOperand()) {
+    const MachineMemOperand *MMO = *MI->memoperands_begin();
+
+    // Don't touch volatile memory accesses - we may be changing their order.
+    if (MMO->isVolatile())
+      return false;
+
+    // Unaligned ldr/str is emulated by some kernels, but unaligned ldm/stm is not.
+    if (MMO->getAlignment() < 4)
+      return false;
+  }
+
   int Opcode = MI->getOpcode();
   switch (Opcode) {
   default: break;