Implement bottom-up fast-isel. This has the advantage of not requiring

a separate DCE pass over MachineInstrs.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@107804 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 12 deletions

diff --git a/lib/CodeGen/LLVMTargetMachine.cpp b/lib/CodeGen/LLVMTargetMachine.cpp
index d437370031..bf3137e495 100644
--- a/lib/CodeGen/LLVMTargetMachine.cpp
+++ b/lib/CodeGen/LLVMTargetMachine.cpp
@@ -329,19 +329,15 @@ bool LLVMTargetMachine::addCommonCodeGenPasses(PassManagerBase &PM,
   if (OptLevel != CodeGenOpt::None)
     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);
-
   if (OptLevel != CodeGenOpt::None) {
+    // 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);
+
     PM.add(createOptimizeExtsPass());
     if (!DisableMachineLICM)
       PM.add(createMachineLICMPass());