[NVPTXAsmPrinter] do not print .align on function headers

[jingyue]

Summary

PTX does not allow .align directives on function headers.

Fixes PR21551.

[eliben]

LGTM

[jholewinski]

LGTM. Thanks!

include/llvm/MC/MCAsmInfo.h

protected:
   /// True is .comm's and .lcomms optional alignment is to be specified in bytes
   /// instead of log2(n).  Defaults to true.
   bool COMMDirectiveAlignmentIsInBytes;
 
   /// Describes if the .lcomm directive for the target supports an alignment
   /// argument and how it is interpreted.  Defaults to NoAlignment.
   LCOMM::LCOMMType LCOMMDirectiveAlignmentType;
 
+  // True if the target allows .align directives on funtions. This is true for
+  // most targets, so defaults to true.
+  bool HasFunctionAlignment;
+
   /// True if the target has .type and .size directives, this is true for most
   /// ELF targets.  Defaults to true.
   bool HasDotTypeDotSizeDirective;
 
   /// True if the target has a single parameter .file directive, this is true
   /// for ELF targets.  Defaults to true.
   bool HasSingleParameterDotFile;
 
public:
   }
   bool hasAggressiveSymbolFolding() const { return HasAggressiveSymbolFolding; }
   bool getCOMMDirectiveAlignmentIsInBytes() const {
     return COMMDirectiveAlignmentIsInBytes;
   }
   LCOMM::LCOMMType getLCOMMDirectiveAlignmentType() const {
     return LCOMMDirectiveAlignmentType;
   }
+  bool hasFunctionAlignment() const { return HasFunctionAlignment; }
   bool hasDotTypeDotSizeDirective() const { return HasDotTypeDotSizeDirective; }
   bool hasSingleParameterDotFile() const { return HasSingleParameterDotFile; }
   bool hasIdentDirective() const { return HasIdentDirective; }
   bool hasNoDeadStrip() const { return HasNoDeadStrip; }
   const char *getWeakDirective() const { return WeakDirective; }
   const char *getWeakRefDirective() const { return WeakRefDirective; }
   bool hasWeakDefDirective() const { return HasWeakDefDirective; }
   bool hasWeakDefCanBeHiddenDirective() const {

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

void AsmPrinter::EmitFunctionHeader() {
   // Print the 'header' of function.
   const Function *F = MF->getFunction();
 
   OutStreamer.SwitchSection(
       getObjFileLowering().SectionForGlobal(F, *Mang, TM));
   EmitVisibility(CurrentFnSym, F->getVisibility());
 
   EmitLinkage(F, CurrentFnSym);
+  if (MAI->hasFunctionAlignment())
     EmitAlignment(MF->getAlignment(), F);
 
   if (MAI->hasDotTypeDotSizeDirective())
     OutStreamer.EmitSymbolAttribute(CurrentFnSym, MCSA_ELF_TypeFunction);
 
   if (isVerbose()) {
     F->printAsOperand(OutStreamer.GetCommentOS(),
                    /*PrintType=*/false, F->getParent());
     OutStreamer.GetCommentOS() << '\n';

lib/MC/MCAsmInfo.cpp

MCAsmInfo::MCAsmInfo() {
   TextAlignFillValue = 0;
   GPRel64Directive = nullptr;
   GPRel32Directive = nullptr;
   GlobalDirective = "\t.globl\t";
   SetDirectiveSuppressesReloc = false;
   HasAggressiveSymbolFolding = true;
   COMMDirectiveAlignmentIsInBytes = true;
   LCOMMDirectiveAlignmentType = LCOMM::NoAlignment;
+  HasFunctionAlignment = true;
   HasDotTypeDotSizeDirective = true;
   HasSingleParameterDotFile = true;
   HasIdentDirective = false;
   HasNoDeadStrip = false;
   WeakDirective = "\t.weak\t";
   WeakRefDirective = nullptr;
   HasWeakDefDirective = false;
   HasWeakDefCanBeHiddenDirective = false;

lib/Target/NVPTX/MCTargetDesc/NVPTXMCAsmInfo.cpp

NVPTXMCAsmInfo::NVPTXMCAsmInfo(StringRef TT) {
   CommentString = "//";
 
   HasSingleParameterDotFile = false;
 
   InlineAsmStart = " inline asm";
   InlineAsmEnd = " inline asm";
 
   SupportsDebugInformation = CompileForDebugging;
+  // PTX does not allow .align on functions.
+  HasFunctionAlignment = false;
   HasDotTypeDotSizeDirective = false;
 
   Data8bitsDirective = " .b8 ";
   Data16bitsDirective = " .b16 ";
   Data32bitsDirective = " .b32 ";
   Data64bitsDirective = " .b64 ";
   ZeroDirective = " .b8";
   AsciiDirective = " .b8";
   AscizDirective = " .b8";
 
   // @TODO: Can we just disable this?
   WeakDirective = "\t// .weak\t";
   GlobalDirective = "\t// .globl\t";
 }

test/CodeGen/NVPTX/function-align.ll

+; RUN: llc < %s -march=nvptx -mcpu=sm_20 | FileCheck %s
+
+; CHECK-NOT: .align 2
+define ptx_device void @foo() align 2 {
+; CHECK-LABEL: .func foo
+  ret void
+}