[MC] Adding code padding for performance stability - infrastructure. NFC.

Infrastructure designed for padding code with nop instructions in key places such that preformance improvement will be achieved.
The infrastructure is implemented such that the padding is done in the Assembler after the layout is done and all IPs and alignments are known.
This patch by itself in a NFC. Future patches will make use of this infrastructure to implement required policies for code padding.

Reviewers:
aaboud
zvi
craig.topper
gadi.haber

Differential revision: https://reviews.llvm.org/D34393

Change-Id: I92110d0c0a757080a8405636914a93ef6f8ad00e
llvm-svn: 316413

1 files changed, 29 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index b183dde4baf..a35fcdaaf9a 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -73,6 +73,7 @@
 #include "llvm/IR/Type.h"
 #include "llvm/IR/Value.h"
 #include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCCodePadder.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCDirectives.h"
 #include "llvm/MC/MCDwarf.h"
@@ -233,8 +234,7 @@ void AsmPrinter::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.addRequired<MachineModuleInfo>();
   AU.addRequired<MachineOptimizationRemarkEmitterPass>();
   AU.addRequired<GCModuleInfo>();
-  if (isVerbose())
-    AU.addRequired<MachineLoopInfo>();
+  AU.addRequired<MachineLoopInfo>();
 }
 
 bool AsmPrinter::doInitialization(Module &M) {
@@ -1440,8 +1440,7 @@ void AsmPrinter::SetupMachineFunction(MachineFunction &MF) {
   }
 
   ORE = &getAnalysis<MachineOptimizationRemarkEmitterPass>().getORE();
-  if (isVerbose())
-    LI = &getAnalysis<MachineLoopInfo>();
+  LI = &getAnalysis<MachineLoopInfo>();
 
   const TargetSubtargetInfo &STI = MF.getSubtarget();
   EnablePrintSchedInfo = PrintSchedule.getNumOccurrences()
@@ -2614,6 +2613,23 @@ static void emitBasicBlockLoopComments(const MachineBasicBlock &MBB,
   PrintChildLoopComment(OS, Loop, AP.getFunctionNumber());
 }
 
+void AsmPrinter::setupCodePaddingContext(const MachineBasicBlock &MBB,
+                                         MCCodePaddingContext &Context) const {
+  assert(MF != nullptr && "Machine function must be valid");
+  assert(LI != nullptr && "Loop info must be valid");
+  Context.IsPaddingActive = !MF->hasInlineAsm() &&
+                            !MF->getFunction()->optForSize() &&
+                            TM.getOptLevel() != CodeGenOpt::None;
+  const MachineLoop *CurrentLoop = LI->getLoopFor(&MBB);
+  Context.IsBasicBlockInsideInnermostLoop =
+      CurrentLoop != nullptr && CurrentLoop->getSubLoops().empty();
+  Context.IsBasicBlockReachableViaFallthrough =
+      std::find(MBB.pred_begin(), MBB.pred_end(), MBB.getPrevNode()) !=
+      MBB.pred_end();
+  Context.IsBasicBlockReachableViaBranch =
+      MBB.pred_size() > 0 && !isBlockOnlyReachableByFallthrough(&MBB);
+}
+
 /// EmitBasicBlockStart - This method prints the label for the specified
 /// MachineBasicBlock, an alignment (if present) and a comment describing
 /// it if appropriate.
@@ -2629,6 +2645,9 @@ void AsmPrinter::EmitBasicBlockStart(const MachineBasicBlock &MBB) const {
   // Emit an alignment directive for this block, if needed.
   if (unsigned Align = MBB.getAlignment())
     EmitAlignment(Align);
+  MCCodePaddingContext Context;
+  setupCodePaddingContext(MBB, Context);
+  OutStreamer->EmitCodePaddingBasicBlockStart(Context);
 
   // If the block has its address taken, emit any labels that were used to
   // reference the block.  It is possible that there is more than one label
@@ -2670,6 +2689,12 @@ void AsmPrinter::EmitBasicBlockStart(const MachineBasicBlock &MBB) const {
   }
 }
 
+void AsmPrinter::EmitBasicBlockEnd(const MachineBasicBlock &MBB) {
+  MCCodePaddingContext Context;
+  setupCodePaddingContext(MBB, Context);
+  OutStreamer->EmitCodePaddingBasicBlockEnd(Context);
+}
+
 void AsmPrinter::EmitVisibility(MCSymbol *Sym, unsigned Visibility,
                                 bool IsDefinition) const {
   MCSymbolAttr Attr = MCSA_Invalid;