[llvm-commits] [llvm] r106809 - /llvm/trunk/lib/CodeGen/LLVMTargetMachine.cpp

[Dan Gohman]

Author: djg
Date: Thu Jun 24 18:41:59 2010
New Revision: 106809

URL: http://llvm.org/viewvc/llvm-project?rev=106809&view=rev
Log:
Add some comments.

Modified:
    llvm/trunk/lib/CodeGen/LLVMTargetMachine.cpp

Modified: llvm/trunk/lib/CodeGen/LLVMTargetMachine.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/LLVMTargetMachine.cpp?rev=106809&r1=106808&r2=106809&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/LLVMTargetMachine.cpp (original)
+++ llvm/trunk/lib/CodeGen/LLVMTargetMachine.cpp Thu Jun 24 18:41:59 2010
@@ -330,6 +330,13 @@
     PM.add(createOptimizePHIsPass());
 
   // Delete dead machine instructions regardless of optimization level.
+  //
+  // At -O0, fast-isel frequently creates dead instructions.
+  //
+  // With optimization, dead code should already be eliminated. However
+  // there is one known exception: lowered code for arguments that are only
+  // used by tail calls, where the tail calls reuse the incoming stack
+  // arguments directly (see t11 in test/CodeGen/X86/sibcall.ll).
   PM.add(createDeadMachineInstructionElimPass());
   printAndVerify(PM, "After codegen DCE pass",
                  /* allowDoubleDefs= */ true);