Include SelectionDAGISel in the opt-bisect process

[andrew.w.kaylor]

Summary

This patch allows the SelectionDAGISel pass to be put into CodeGenOpt::None mode in response to the opt-bisect-limit command line option in addition to the OptimizeNone function attribute (the skipFunction() call checks both of these conditions).

See D19172 for details on the opt-bisect implementation.

I am checking to see if the optimization level is already CodeGenOpt::None before calling the skipFunction() method in order to avoid introducing test failures in two lit tests which verify that no pass is "skipped" by the optnone or opt-bisect options that is otherwise run at -O0. Calling skipFunction at -O0 wouldn't actually change this pass' behavior, but it would generate a debugging message indicating that the pass was being skipped.

[andrew.w.kaylor]

Adding a test.

llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
   // Reset the target options before resetting the optimization
   // level below.
   // FIXME: This is a horrible hack and should be processed via
   // codegen looking at the optimization level explicitly when
   // it wants to look at it.
   TM.resetTargetOptions(Fn);
   // Reset OptLevel to None for optnone functions.
   CodeGenOpt::Level NewOptLevel = OptLevel;
-  if (Fn.hasFnAttribute(Attribute::OptimizeNone))
+  if (OptLevel != CodeGenOpt::None && skipFunction(Fn))
     NewOptLevel = CodeGenOpt::None;
   OptLevelChanger OLC(*this, NewOptLevel);
 
   TII = MF->getSubtarget().getInstrInfo();
   TLI = MF->getSubtarget().getTargetLowering();
   RegInfo = &MF->getRegInfo();
   AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
   LibInfo = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();

llvm/trunk/test/Other/X86/opt-bisect-isel.ll

+; This test verifies that no optimizations are performed on the @f function
+; when the -opt-bisect-limit=0 option is used.  In particular, the X86
+; instruction selector will optimize the cmp instruction to a sub instruction
+; if it is not run in -O0 mode.
+
+; RUN: llc -O3 -opt-bisect-limit=0 -o - %s | FileCheck %s
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @f() {
+entry:
+  %cmp = icmp slt i32 undef, 8
+  br i1 %cmp, label %middle, label %end
+
+middle:
+  br label %end
+
+end:
+  ret void
+}
+
+; CHECK: cmpl $8, %eax