[bugpoint] Add support for -Oz and properly enable -Os.

[fhahn]

Summary

This patch adds -Oz as option and also properly enables support for -Os.
Currently, the existing check for -Os is dead, because the enclosing if
only checks of O1, O2 and O3.

There is still a difference between the -Oz pipeline compared to opt,
but I have not been able to track that down yet.

[efriedma]

LGTM

I took a quick glance at what opt is doing, and I see a few differences that likely matter:

1. bugpoint never calls createTargetTransformInfoWrapperPass
2. bugpoint never calls adjustPassManager
3. bugpoint doesn't tweak Builder.LoopVectorize/Builder.SLPVectorize the same way

[fhahn]

In D67593#1671961, @efriedma wrote:

LGTM

I took a quick glance at what opt is doing, and I see a few differences that likely matter:

1. bugpoint never calls createTargetTransformInfoWrapperPass
2. bugpoint never calls adjustPassManager
3. bugpoint doesn't tweak Builder.LoopVectorize/Builder.SLPVectorize the same way

Yep, I'll look into making additional adjustments as follow-ups.

llvm/tools/bugpoint/bugpoint.cpp

static cl::opt<bool>
     OptLevelO2("O2", cl::desc("Optimization level 2. Identical to 'opt -O2'"));
 
 static cl::opt<bool> OptLevelOs(
     "Os",
     cl::desc(
         "Like -O2 with extra optimizations for size. Similar to clang -Os"));
 
 static cl::opt<bool>
+OptLevelOz("Oz",
+           cl::desc("Like -Os but reduces code size further. Similar to clang -Oz"));
+
+static cl::opt<bool>
     OptLevelO3("O3", cl::desc("Optimization level 3. Identical to 'opt -O3'"));
 
 static cl::opt<std::string>
     OverrideTriple("mtriple", cl::desc("Override target triple for module"));
 
 /// BugpointIsInterrupted - Set to true when the user presses ctrl-c.
 bool llvm::BugpointIsInterrupted = false;
 
public:
   void add(Pass *P) override {
     const void *ID = P->getPassID();
     const PassInfo *PI = PassRegistry::getPassRegistry()->getPassInfo(ID);
     D.addPass(PI->getPassArgument());
   }
 };
 }
 
+// This routine adds optimization passes based on selected optimization level,
+// OptLevel.
+//
+// OptLevel - Optimization Level
+static void AddOptimizationPasses(legacy::FunctionPassManager &FPM,
+                                  unsigned OptLevel,
+                                  unsigned SizeLevel) {
+  PassManagerBuilder Builder;
+  Builder.OptLevel = OptLevel;
+  Builder.SizeLevel = SizeLevel;
+
+  if (OptLevel > 1)
+    Builder.Inliner = createFunctionInliningPass(OptLevel, SizeLevel, false);
+  else
+    Builder.Inliner = createAlwaysInlinerLegacyPass();
+
+  Builder.populateFunctionPassManager(FPM);
+  Builder.populateModulePassManager(FPM);
+}
+
 #ifdef LINK_POLLY_INTO_TOOLS
 namespace polly {
 void initializePollyPasses(llvm::PassRegistry &Registry);
 }
 #endif
 
 int main(int argc, char **argv) {
 #ifndef DEBUG_BUGPOINT
#endif
   AddToDriver PM(D);
 
   if (StandardLinkOpts) {
     PassManagerBuilder Builder;
     Builder.Inliner = createFunctionInliningPass();
     Builder.populateLTOPassManager(PM);
   }
 
-  if (OptLevelO1 || OptLevelO2 || OptLevelO3) {
-    PassManagerBuilder Builder;
-    if (OptLevelO1)
-      Builder.Inliner = createAlwaysInlinerLegacyPass();
-    else if (OptLevelOs || OptLevelO2)
-      Builder.Inliner = createFunctionInliningPass(
-          2, OptLevelOs ? 1 : 0, false);
-    else
-      Builder.Inliner = createFunctionInliningPass(275);
-    Builder.populateFunctionPassManager(PM);
-    Builder.populateModulePassManager(PM);
-  }
+    AddOptimizationPasses(PM, 1, 0);
+  else if (OptLevelO2)
+    AddOptimizationPasses(PM, 2, 0);
+  else if (OptLevelO3)
+    AddOptimizationPasses(PM, 3, 0);
+  else if (OptLevelOs)
+    AddOptimizationPasses(PM, 2, 1);
+  else if (OptLevelOz)
+    AddOptimizationPasses(PM, 2, 2);
 
   for (const PassInfo *PI : PassList)
     D.addPass(PI->getPassArgument());
 
 // Bugpoint has the ability of generating a plethora of core files, so to
 // avoid filling up the disk, we prevent it
 #ifndef DEBUG_BUGPOINT
   sys::Process::PreventCoreFiles();
 #endif
 
   if (Error E = D.run()) {
     errs() << toString(std::move(E));
     return 1;
   }
   return 0;
 }