[ARM][MC] Add GNU Alias for ldrexd, ldaexd, stlexd, and strexd instructions (#86507)

These aliases were supported previously there was a regression at some point.

This adds back the alternate forms and tidies up this section of code a little.

See #83436 (comment) for the initial report regarding this change.

Author: AlfieRichardsArm

llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp

@@ -6865,8 +6865,9 @@ static void applyMnemonicAliases(StringRef &Mnemonic,
                                  const FeatureBitset &Features,
                                  unsigned VariantID);
 
-// The GNU assembler has aliases of ldrd and strd with the second register
-// omitted. We don't have a way to do that in tablegen, so fix it up here.
+// The GNU assembler has aliases of ldrd, strd, ldrexd, strexd, ldaexd, and
+// stlexd with the second register omitted. We don't have a way to do that in
+// tablegen, so fix it up here.
 //
 // We have to be careful to not emit an invalid Rt2 here, because the rest of
 // the assembly parser could then generate confusing diagnostics refering to
@@ -6876,13 +6877,19 @@ static void applyMnemonicAliases(StringRef &Mnemonic,
 void ARMAsmParser::fixupGNULDRDAlias(StringRef Mnemonic,
                                      OperandVector &Operands,
                                      unsigned MnemonicOpsEndInd) {
-  if (Mnemonic != "ldrd" && Mnemonic != "strd")
+  if (Mnemonic != "ldrd" && Mnemonic != "strd" && Mnemonic != "ldrexd" &&
+      Mnemonic != "strexd" && Mnemonic != "ldaexd" && Mnemonic != "stlexd")
     return;
-  if (Operands.size() < MnemonicOpsEndInd + 2)
+
+  unsigned IdX = Mnemonic == "strexd" || Mnemonic == "stlexd"
+                     ? MnemonicOpsEndInd + 1
+                     : MnemonicOpsEndInd;
+
+  if (Operands.size() < IdX + 2)
     return;
 
-  ARMOperand &Op2 = static_cast<ARMOperand &>(*Operands[MnemonicOpsEndInd]);
-  ARMOperand &Op3 = static_cast<ARMOperand &>(*Operands[MnemonicOpsEndInd + 1]);
+  ARMOperand &Op2 = static_cast<ARMOperand &>(*Operands[IdX]);
+  ARMOperand &Op3 = static_cast<ARMOperand &>(*Operands[IdX + 1]);
 
   if (!Op2.isReg())
     return;
@@ -6907,7 +6914,7 @@ void ARMAsmParser::fixupGNULDRDAlias(StringRef Mnemonic,
     return;
 
   Operands.insert(
-      Operands.begin() + MnemonicOpsEndInd + 1,
+      Operands.begin() + IdX + 1,
       ARMOperand::CreateReg(PairedReg, Op2.getStartLoc(), Op2.getEndLoc()));
 }
 
@@ -7336,47 +7343,53 @@ bool ARMAsmParser::ParseInstruction(ParseInstructionInfo &Info, StringRef Name,
       static_cast<ARMOperand &>(*Operands[MnemonicOpsEndInd]).isImm())
     removeCondCode(Operands, MnemonicOpsEndInd);
 
+  // GNU Assembler extension (compatibility).
+  fixupGNULDRDAlias(Mnemonic, Operands, MnemonicOpsEndInd);
+
   // Adjust operands of ldrexd/strexd to MCK_GPRPair.
   // ldrexd/strexd require even/odd GPR pair. To enforce this constraint,
   // a single GPRPair reg operand is used in the .td file to replace the two
   // GPRs. However, when parsing from asm, the two GRPs cannot be
   // automatically
   // expressed as a GPRPair, so we have to manually merge them.
   // FIXME: We would really like to be able to tablegen'erate this.
-  if (!isThumb() && Operands.size() > MnemonicOpsEndInd + 1 &&
+  bool IsLoad = (Mnemonic == "ldrexd" || Mnemonic == "ldaexd");
+  if (!isThumb() && Operands.size() > MnemonicOpsEndInd + 1 + (!IsLoad) &&
       (Mnemonic == "ldrexd" || Mnemonic == "strexd" || Mnemonic == "ldaexd" ||
        Mnemonic == "stlexd")) {
-    bool isLoad = (Mnemonic == "ldrexd" || Mnemonic == "ldaexd");
-    unsigned Idx = isLoad ? MnemonicOpsEndInd : MnemonicOpsEndInd + 1;
+    unsigned Idx = IsLoad ? MnemonicOpsEndInd : MnemonicOpsEndInd + 1;
     ARMOperand &Op1 = static_cast<ARMOperand &>(*Operands[Idx]);
     ARMOperand &Op2 = static_cast<ARMOperand &>(*Operands[Idx + 1]);
 
     const MCRegisterClass &MRC = MRI->getRegClass(ARM::GPRRegClassID);
-    // Adjust only if Op1 and Op2 are GPRs.
-    if (Op1.isReg() && Op2.isReg() && MRC.contains(Op1.getReg()) &&
-        MRC.contains(Op2.getReg())) {
+    // Adjust only if Op1 is a GPR.
+    if (Op1.isReg() && MRC.contains(Op1.getReg())) {
       unsigned Reg1 = Op1.getReg();
-      unsigned Reg2 = Op2.getReg();
       unsigned Rt = MRI->getEncodingValue(Reg1);
+      unsigned Reg2 = Op2.getReg();
       unsigned Rt2 = MRI->getEncodingValue(Reg2);
-
-      // Rt2 must be Rt + 1 and Rt must be even.
-      if (Rt + 1 != Rt2 || (Rt & 1)) {
+      // Rt2 must be Rt + 1.
+      if (Rt + 1 != Rt2)
         return Error(Op2.getStartLoc(),
-                     isLoad ? "destination operands must be sequential"
+                     IsLoad ? "destination operands must be sequential"
                             : "source operands must be sequential");
-      }
+
+      // Rt must be even
+      if (Rt & 1)
+        return Error(
+            Op1.getStartLoc(),
+            IsLoad ? "destination operands must start start at an even register"
+                   : "source operands must start start at an even register");
+
       unsigned NewReg = MRI->getMatchingSuperReg(
           Reg1, ARM::gsub_0, &(MRI->getRegClass(ARM::GPRPairRegClassID)));
+
       Operands[Idx] =
           ARMOperand::CreateReg(NewReg, Op1.getStartLoc(), Op2.getEndLoc());
       Operands.erase(Operands.begin() + Idx + 1);
     }
   }
 
-  // GNU Assembler extension (compatibility).
-  fixupGNULDRDAlias(Mnemonic, Operands, MnemonicOpsEndInd);
-
   // FIXME: As said above, this is all a pretty gross hack.  This instruction
   // does not fit with other "subs" and tblgen.
   // Adjust operands of B9.3.19 SUBS PC, LR, #imm (Thumb2) system instruction

llvm/test/MC/ARM/basic-arm-instructions.s

@@ -1202,6 +1202,10 @@ Lforward:
 @ CHECK: ldrex	r1, [r7]                @ encoding: [0x9f,0x1f,0x97,0xe1]
 @ CHECK: ldrexd	r6, r7, [r8]            @ encoding: [0x9f,0x6f,0xb8,0xe1]
 
+@ GNU alias
+        ldrexd  r6, [r8]
+@ CHECK: ldrexd	r6, r7, [r8]            @ encoding: [0x9f,0x6f,0xb8,0xe1]
+
 @------------------------------------------------------------------------------
 @ LDRHT
 @------------------------------------------------------------------------------
@@ -2904,6 +2908,10 @@ Lforward:
 @ CHECK: strex	r2, r1, [r7]            @ encoding: [0x91,0x2f,0x87,0xe1]
 @ CHECK: strexd	r6, r2, r3, [r8]        @ encoding: [0x92,0x6f,0xa8,0xe1]
 
+@ GNU alias
+        strexd  r6, r2, [r8]
+@ CHECK: strexd	r6, r2, r3, [r8]        @ encoding: [0x92,0x6f,0xa8,0xe1]
+
 @------------------------------------------------------------------------------
 @ STR
 @------------------------------------------------------------------------------

llvm/test/MC/ARM/load-store-acquire-release-v8-thumb.s

@@ -14,6 +14,10 @@
 @ CHECK-V7: error: instruction requires: acquire/release
 @ CHECK-V7: error: instruction requires: acquire/release
 
+@ GNU alias
+        ldaexd  r6, [r8]
+@ CHECK:  ldaexd	r6, r7, [r8]            @ encoding: [0xd8,0xe8,0xff,0x67]
+
         stlexb  r1, r3, [r4]
         stlexh  r4, r2, [r5]
         stlex  r2, r1, [r7]
@@ -27,6 +31,10 @@
 @ CHECK-V7: error: instruction requires: acquire/release
 @ CHECK-V7: error: instruction requires: acquire/release
 
+@ GNU alias
+        stlexd  r6, r2, [r8]
+@ CHECK: stlexd r6, r2, r3, [r8]        @ encoding: [0xc8,0xe8,0xf6,0x23]
+
          lda r5, [r6]
          ldab r5, [r6]
          ldah r12, [r9]

llvm/test/MC/ARM/load-store-acquire-release-v8.s

@@ -1,4 +1,5 @@
-@ RUN: llvm-mc -triple=armv8 -show-encoding < %s | FileCheck %s
+@ RUN: not llvm-mc -triple=armv8 -show-encoding < %s 2> %t | FileCheck %s
+@ RUN: FileCheck %s < %t --check-prefix=CHECK-ERROR
 @ RUN: not llvm-mc -triple=armv7 -show-encoding < %s 2>&1 | FileCheck %s --check-prefix=CHECK-V7
         ldaexb  r3, [r4]
         ldaexh  r2, [r5]
@@ -14,6 +15,13 @@
 @ CHECK-V7: instruction requires: acquire/release
 @ CHECK-V7: instruction requires: acquire/release
 
+        ldaexd  r2, r4, [r8]
+@ CHECK-ERROR: error: destination operands must be sequential
+
+@ GNU alias
+        ldaexd  r6, [r8]
+@ CHECK:  ldaexd	r6, r7, [r8]            @ encoding: [0x9f,0x6e,0xb8,0xe1]
+
         stlexb  r1, r3, [r4]
         stlexh  r4, r2, [r5]
         stlex  r2, r1, [r7]
@@ -27,6 +35,13 @@
 @ CHECK-V7: instruction requires: acquire/release
 @ CHECK-V7: instruction requires: acquire/release
 
+        stlexd  r6, r2, r4, [r8]
+@ CHECK-ERROR: error: source operands must be sequential
+
+@ GNU alias
+        stlexd  r6, r2, [r8]
+@ CHECK: stlexd r6, r2, r3, [r8]        @ encoding: [0x92,0x6e,0xa8,0xe1]
+
          lda r5, [r6]
          ldab r5, [r6]
          ldah r12, [r9]