SelectionDAGISel can now natively handle Switch instructions, in the same

manner that the LowerSwitch LLVM to LLVM pass does: emitting a binary
search tree of basic blocks.  The new approach has several advantages:
it is faster, it generates significantly smaller code in many cases, and
it paves the way for implementing dense switch tables as a jump table by
handling switches directly in the instruction selector.

This functionality is currently only enabled on x86, but should be safe for
every target.  In anticipation of making it the default, the cfg is now
properly updated in the x86, ppc, and sparc select lowering code.

llvm-svn: 27156

1 files changed, 7 insertions, 4 deletions

diff --git a/llvm/lib/Target/X86/X86TargetMachine.cpp b/llvm/lib/Target/X86/X86TargetMachine.cpp
index f6d34ea2df5..44877d9b4d1 100644
--- a/llvm/lib/Target/X86/X86TargetMachine.cpp
+++ b/llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -36,7 +36,8 @@ namespace {
   cl::opt<bool> DisableOutput("disable-x86-llc-output", cl::Hidden,
                               cl::desc("Disable the X86 asm printer, for use "
                                        "when profiling the code generator."));
-
+  cl::opt<bool> DisableLowerSwitch("disable-lower-switch", cl::Hidden,
+                                   cl::desc("Disable the LowerSwitch pass"));
   // Register the target.
   RegisterTarget<X86TargetMachine> X("x86", "  IA-32 (Pentium and above)");
 }
@@ -100,8 +101,9 @@ bool X86TargetMachine::addPassesToEmitFile(PassManager &PM, std::ostream &Out,
   PM.add(createLowerInvokePass());
 
   // FIXME: Implement the switch instruction in the instruction selector!
-  PM.add(createLowerSwitchPass());
-
+  if (!DisableLowerSwitch)
+    PM.add(createLowerSwitchPass());
+  
   // Make sure that no unreachable blocks are instruction selected.
   PM.add(createUnreachableBlockEliminationPass());
 
@@ -168,7 +170,8 @@ void X86JITInfo::addPassesToJITCompile(FunctionPassManager &PM) {
   PM.add(createLowerInvokePass());
 
   // FIXME: Implement the switch instruction in the instruction selector!
-  PM.add(createLowerSwitchPass());
+  if (!DisableLowerSwitch)
+    PM.add(createLowerSwitchPass());
 
   // Make sure that no unreachable blocks are instruction selected.
   PM.add(createUnreachableBlockEliminationPass());