[AVX512][inline-asm] Fix AVX512 inline assembly instruction resolution when the size qualifier of a memory operand is not specified explicitly.

[coby]

Summary

This commit handles cases where the size qualifier of an indirect memory reference operand in Intel syntax is missing (e.g. "vaddps xmm1, xmm2, [a]").

GCC will deduce the size qualifier for AVX512 vector and broadcast memory operands based on the possible matches:
"vaddps xmm1, xmm2, [a]" matches only “XMMWORD PTR” qualifier.
"vaddps xmm1, xmm2, [a]{1to4}" matches only “DWORD PTR” qualifier.

This is different from the current behavior of LLVM, which deduces the size qualifier based on the size of the memory operand.
For "vaddps xmm1, xmm2, [a]"
"char a;" will imply "BYTE PTR" qualifier
"short a;" will imply "WORD PTR" qualifier.

This commit aligns LLVM to GCC’s behavior.

This is the LLVM part of the review.
The Clang part of the review: https://reviews.llvm.org/D26587

Differential Revision: https://reviews.llvm.org/D26586

[myatsina]

lib/Target/X86/AsmParser/X86AsmParser.cpp

769 ↗

(On Diff #77740)

Please add description above the function.

1179 ↗

(On Diff #77740)

I think this name is a but misleading.
How about "KeepMemUnsized" or "AllowBetterSizeMatch"?

1209 ↗

(On Diff #77740)

Please clang-format your patch.
handle --> Handle

1211 ↗

(On Diff #77740)

then --> than

2858 ↗

(On Diff #77740)

why the break? why not put the inquiring logic here?
Is there some other code path that might reach the inquiring logic?

2895 ↗

(On Diff #77740)

Why the break?

2959 ↗

(On Diff #77740)

pan?

2998 ↗

(On Diff #77740)

online --> only ?

3000 ↗

(On Diff #77740)

a

3000 ↗

(On Diff #77740)

Ignore this comment :)

[delena]

lib/Target/X86/AsmParser/X86AsmParser.cpp

2848 ↗

(On Diff #78680)

Put "assert" instead of "if".

2885 ↗

(On Diff #78680)

IA allows only one memory operand per instruction.
if (UnsizedMemOp) {

UnsizedMemOpNext = X86Op;
break;

}
UnsizedMemOp = X86Op;

[coby]

lib/Target/X86/AsmParser/X86AsmParser.cpp

2848 ↗

(On Diff #78680)

Cannot assert at this point. This function is called regardless of the platform.

2885 ↗

(On Diff #78680)

Previous revision addressed this issue exactly, and was rejected. I found it redundant (and wrong) to continue looking past the first interception of an unsized mem op.
Having said that - both approaches are congregated to the same behavior.
If Marina won't furthermore object - I'm keen to revert to previous approach.

[myatsina]

LGTM (in condition you'll fix the typos and return to the break as Elena mentioned).

Also,
please clarify the summary of this review.

lib/Target/X86/AsmParser/X86AsmParser.cpp

1209 ↗

(On Diff #77740)

Still relevant:
handle --> Handle

771 ↗

(On Diff #78680)

Rephrase (don't forget to clang-format):

Obtain an appropriate size qualifier, when the AVX512 vector/broadcast memory operand is missing a qualifier.

2885 ↗

(On Diff #78680)

If we're returning the break then please add a comment that we handle here only cases that have one undefined memory operand, and if an instruction has more than one memory operand we will fail later on when we'll try to match an instruction.

2955 ↗

(On Diff #78680)

te --> the

[rnk]

I feel like we need to step back and ask why we are using the variable size information provided by the frontend at all. I don't think MSVC uses it. We probably only needed it because our intel asm matcher couldn't cope with ambiguity before and it was getting the wrong sizes.

I'm going to look into removing the frontend-directed AOK_SizeDirective rewrite altogether.

llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp

1208

It seems ridiculous to emit this size directive modification here and then rewrite it later in the asm matcher. Surely there is a better way to do this.

1210

This code is not properly indented, and this actually confused me while reading the committed code.

1213

typo on "mechanism"

1504

We are always parsing inline asm when calling CreateMemForInlineAsm, that's why we're here.

2845

This seems unnecessary, which makes sense because your follow-up change D32636 removes it

[rnk]

In D26586#746128, @rnk wrote:

I feel like we need to step back and ask why we are using the variable size information provided by the frontend at all. I don't think MSVC uses it. We probably only needed it because our intel asm matcher couldn't cope with ambiguity before and it was getting the wrong sizes.

I'm going to look into removing the frontend-directed AOK_SizeDirective rewrite altogether.

I looked into this more and commented on the new patch D32636

llvm/trunk/lib/Target/X86/AsmParser/X86AsmParser.cpp

bool ParseIntelIdentifier(const MCExpr *&Val, StringRef &Identifier,
                             bool IsUnevaluatedOperand, SMLoc &End);
 
   std::unique_ptr<X86Operand> ParseMemOperand(unsigned SegReg, SMLoc StartLoc);
 
   std::unique_ptr<X86Operand>
   CreateMemForInlineAsm(unsigned SegReg, const MCExpr *Disp, unsigned BaseReg,
                         unsigned IndexReg, unsigned Scale, SMLoc Start,
                         SMLoc End, unsigned Size, StringRef Identifier,
-                        InlineAsmIdentifierInfo &Info);
+                        InlineAsmIdentifierInfo &Info,
+                        bool AllowBetterSizeMatch = false);
 
   bool parseDirectiveEven(SMLoc L);
   bool ParseDirectiveWord(unsigned Size, SMLoc L);
   bool ParseDirectiveCode(StringRef IDVal, SMLoc L);
 
   bool processInstruction(MCInst &Inst, const OperandVector &Ops);
 
   /// Wrapper around MCStreamer::EmitInstruction(). Possibly adds
private:
   /// Parses AVX512 specific operand primitives: masked registers ({%k<NUM>}, {z})
   /// and memory broadcasting ({1to<NUM>}) primitives, updating Operands vector if required.
   /// return false if no parsing errors occurred, true otherwise.
   bool HandleAVX512Operand(OperandVector &Operands,
                            const MCParsedAsmOperand &Op);
 
   bool ParseZ(std::unique_ptr<X86Operand> &Z, const SMLoc &StartLoc);
 
+  /// MS-compatibility:
+  /// Obtain an appropriate size qualifier, when facing its absence,
+  /// upon AVX512 vector/broadcast memory operand
+  unsigned AdjustAVX512Mem(unsigned Size, X86Operand* UnsizedMemOpNext);
+
   bool is64BitMode() const {
     // FIXME: Can tablegen auto-generate this?
     return getSTI().getFeatureBits()[X86::Mode64Bit];
   }
   bool is32BitMode() const {
     // FIXME: Can tablegen auto-generate this?
     return getSTI().getFeatureBits()[X86::Mode32Bit];
   }
unsigned Size = StringSwitch<unsigned>(OpStr)
     .Cases("OPAQUE", "opaque", -1U) // needs to be non-zero, but doesn't matter
     .Default(0);
   return Size;
 }
 
 std::unique_ptr<X86Operand> X86AsmParser::CreateMemForInlineAsm(
     unsigned SegReg, const MCExpr *Disp, unsigned BaseReg, unsigned IndexReg,
     unsigned Scale, SMLoc Start, SMLoc End, unsigned Size, StringRef Identifier,
-    InlineAsmIdentifierInfo &Info) {
+    InlineAsmIdentifierInfo &Info, bool AllowBetterSizeMatch) {
   // If we found a decl other than a VarDecl, then assume it is a FuncDecl or
   // some other label reference.
   if (isa<MCSymbolRefExpr>(Disp) && Info.OpDecl && !Info.IsVarDecl) {
     // Insert an explicit size if the user didn't have one.
     if (!Size) {
       Size = getPointerWidth();
       InstInfo->AsmRewrites->emplace_back(AOK_SizeDirective, Start,
                                           /*Len=*/0, Size);
std::unique_ptr<X86Operand> X86AsmParser::CreateMemForInlineAsm(
   // calculation purposes.
   const MCBinaryExpr *BinOp = dyn_cast<MCBinaryExpr>(Disp);
   bool IsSymRef =
       isa<MCSymbolRefExpr>(BinOp ? BinOp->getLHS() : Disp);
   if (IsSymRef) {
     if (!Size) {
       Size = Info.Type * 8; // Size is in terms of bits in this context.
       if (Size)
         InstInfo->AsmRewrites->emplace_back(AOK_SizeDirective, Start,
                                             /*Len=*/0, Size);
+    if (AllowBetterSizeMatch)
+      // Handle cases where size qualifier is absent, upon an indirect symbol
+      // reference - e.g. "vaddps zmm1, zmm2, [var]"
+      // set Size to zero to allow matching mechansim to try and find a better
+      // size qualifier than our initial guess, based on available variants of
+      // the given instruction
+      Size = 0;
     }
   }
 
   // When parsing inline assembly we set the base register to a non-zero value
   // if we don't know the actual value at this time.  This is necessary to
   // get the matching correct in some cases.
   BaseReg = BaseReg ? BaseReg : 1;
   return X86Operand::CreateMem(getPointerWidth(), SegReg, Disp, BaseReg,
if (CheckBaseRegAndIndexReg(BaseReg, IndexReg, ErrMsg)) {
       return nullptr;
     }
     return X86Operand::CreateMem(getPointerWidth(), SegReg, Disp, BaseReg,
                                  IndexReg, Scale, Start, End, Size);
   }
 
   InlineAsmIdentifierInfo &Info = SM.getIdentifierInfo();
   return CreateMemForInlineAsm(SegReg, Disp, BaseReg, IndexReg, Scale, Start,
-                               End, Size, SM.getSymName(), Info);
+                               End, Size, SM.getSymName(), Info,
+                               isParsingInlineAsm());
 }
 
 // Inline assembly may use variable names with namespace alias qualifiers.
 bool X86AsmParser::ParseIntelIdentifier(const MCExpr *&Val,
                                         StringRef &Identifier,
                                         InlineAsmIdentifierInfo &Info,
                                         bool IsUnevaluatedOperand, SMLoc &End) {
   MCAsmParser &Parser = getParser();
bool X86AsmParser::MatchAndEmitATTInstruction(SMLoc IDLoc, unsigned &Opcode,
   }
 
   // If all of these were an outright failure, report it in a useless way.
   Error(IDLoc, "unknown use of instruction mnemonic without a size suffix",
         EmptyRange, MatchingInlineAsm);
   return true;
 }
 
+unsigned X86AsmParser::AdjustAVX512Mem(unsigned Size,
+    X86Operand* UnsizedMemOpNext) {
+  // Check for the existence of an AVX512 platform
+  if (!getSTI().getFeatureBits()[X86::FeatureAVX512])
+    return 0;
+  // Allow adjusting upon a (x|y|z)mm
+  if (Size == 512 || Size == 256 || Size == 128)
+    return Size;
+  // This is an allegadly broadcasting mem op adjustment,
+  // allow some more inquiring to validate it
+  if (Size == 64 || Size == 32)
+    return UnsizedMemOpNext && UnsizedMemOpNext->isToken() &&
+      UnsizedMemOpNext->getToken().substr(0, 4).equals("{1to") ? Size : 0;
+  // Do not allow any other type of adjustments
+  return 0;
+}
+
 bool X86AsmParser::MatchAndEmitIntelInstruction(SMLoc IDLoc, unsigned &Opcode,
                                                 OperandVector &Operands,
                                                 MCStreamer &Out,
                                                 uint64_t &ErrorInfo,
                                                 bool MatchingInlineAsm) {
   assert(!Operands.empty() && "Unexpect empty operand list!");
   X86Operand &Op = static_cast<X86Operand &>(*Operands[0]);
   assert(Op.isToken() && "Leading operand should always be a mnemonic!");
   StringRef Mnemonic = Op.getToken();
   SMRange EmptyRange = None;
   StringRef Base = Op.getToken();
 
   // First, handle aliases that expand to multiple instructions.
   MatchFPUWaitAlias(IDLoc, Op, Operands, Out, MatchingInlineAsm);
 
   MCInst Inst;
 
   // Find one unsized memory operand, if present.
   X86Operand *UnsizedMemOp = nullptr;
+  // If unsized memory operand was found - obtain following operand.
+  // For use in AdjustAVX512Mem
+  X86Operand *UnsizedMemOpNext = nullptr;
   for (const auto &Op : Operands) {
     X86Operand *X86Op = static_cast<X86Operand *>(Op.get());
+    if (UnsizedMemOp) {
+      UnsizedMemOpNext = X86Op;
+      // Have we found an unqualified memory operand,
+      // break. IA allows only one memory operand.
+      break;
+    }
     if (X86Op->isMemUnsized())
       UnsizedMemOp = X86Op;
   }
 
   // Allow some instructions to have implicitly pointer-sized operands.  This is
   // compatible with gas.
   if (UnsizedMemOp) {
     static const char *const PtrSizedInstrs[] = {"call", "jmp", "push"};
if (X86Op->isImm()) {
         Op.setTokenValue(Base);
       }
     }
   }
 
   // If an unsized memory operand is present, try to match with each memory
   // operand size.  In Intel assembly, the size is not part of the instruction
   // mnemonic.
+  unsigned MatchedSize = 0;
   if (UnsizedMemOp && UnsizedMemOp->isMemUnsized()) {
     static const unsigned MopSizes[] = {8, 16, 32, 64, 80, 128, 256, 512};
     for (unsigned Size : MopSizes) {
       UnsizedMemOp->Mem.Size = Size;
       uint64_t ErrorInfoIgnore;
       unsigned LastOpcode = Inst.getOpcode();
       unsigned M = MatchInstruction(Operands, Inst, ErrorInfoIgnore,
                                     MatchingInlineAsm, isParsingIntelSyntax());
       if (Match.empty() || LastOpcode != Inst.getOpcode())
         Match.push_back(M);
 
       // If this returned as a missing feature failure, remember that.
       if (Match.back() == Match_MissingFeature)
         ErrorInfoMissingFeature = ErrorInfoIgnore;
+      if (M == Match_Success)
+        // MS-compatability:
+        // Adjust AVX512 vector/broadcast memory operand,
+        // when facing the absence of a size qualifier.
+        // Match GCC behavior on respective cases.
+        MatchedSize = AdjustAVX512Mem(Size, UnsizedMemOpNext);
     }
 
     // Restore the size of the unsized memory operand if we modified it.
     if (UnsizedMemOp)
       UnsizedMemOp->Mem.Size = 0;
   }
 
   // If we haven't matched anything yet, this is not a basic integer or FPU
bool X86AsmParser::MatchAndEmitIntelInstruction(SMLoc IDLoc, unsigned &Opcode,
   }
 
   // If exactly one matched, then we treat that as a successful match (and the
   // instruction will already have been filled in correctly, since the failing
   // matches won't have modified it).
   unsigned NumSuccessfulMatches =
       std::count(std::begin(Match), std::end(Match), Match_Success);
   if (NumSuccessfulMatches == 1) {
+    if (MatchedSize && isParsingInlineAsm() && isParsingIntelSyntax())
+      // MS compatibility -
+      // Fix the rewrite according to the matched memory size
+      // MS inline assembly only
+      for (AsmRewrite &AR : *InstInfo->AsmRewrites)
+        if ((AR.Loc.getPointer() == UnsizedMemOp->StartLoc.getPointer()) &&
+            (AR.Kind == AOK_SizeDirective))
+          AR.Val = MatchedSize;
     // Some instructions need post-processing to, for example, tweak which
     // encoding is selected. Loop on it while changes happen so the individual
     // transformations can chain off each other.
     if (!MatchingInlineAsm)
       while (processInstruction(Inst, Operands))
         ;
     Inst.setLoc(IDLoc);
     if (!MatchingInlineAsm)