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Merged
merged 1 commit into from
Aug 25, 2025
Merged

[TableGen][DecoderEmitter] Remove dead OPC_Fail #155229

merged 1 commit into from
Aug 25, 2025

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s-barannikov
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It can never be reached. It could be reached if we emitted an opcode that could fall outside the outermost scope, but emission of all such opcodes is guarded by !isOutermostScope().

That also means we never add fixups to the outermost scope, so avoid pushing an entry for it onto the stack.

@s-barannikov
[TableGen][DecoderEmitter] Remove dead OPC_Fail
e634ba4 
It can never be reached. It could be reached if we emitted an opcode
that could fall outside the outermost scope, but emission of all such
opcodes is guarded by `!isOutermostScope()`.
@s-barannikov s-barannikov requested a review from jurahul August 25, 2025 10:16
@llvmbot llvmbot added tablegen llvm:mc Machine (object) code labels Aug 25, 2025
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llvmbot commented Aug 25, 2025

@llvm/pr-subscribers-tablegen

Author: Sergei Barannikov (s-barannikov)

Changes

It can never be reached. It could be reached if we emitted an opcode that could fall outside the outermost scope, but emission of all such opcodes is guarded by !isOutermostScope().

That also means we never add fixups to the outermost scope, so avoid pushing an entry for it onto the stack.

Full diff: https://github.com/llvm/llvm-project/pull/155229.diff

12 Files Affected:

  • (modified) llvm/include/llvm/MC/MCDecoderOps.h (-1)
  • (modified) llvm/test/TableGen/FixedLenDecoderEmitter/additional-encoding.td (-1)
  • (modified) llvm/test/TableGen/FixedLenDecoderEmitter/big-filter.td (+1-2)
  • (modified) llvm/test/TableGen/HwModeEncodeDecode.td (+2-2)
  • (modified) llvm/test/TableGen/HwModeEncodeDecode2.td (+8-8)
  • (modified) llvm/test/TableGen/HwModeEncodeDecode3.td (+21-21)
  • (modified) llvm/test/TableGen/VarLenDecoder.td (+2-2)
  • (modified) llvm/test/TableGen/trydecode-emission.td (+2-2)
  • (modified) llvm/test/TableGen/trydecode-emission2.td (+2-2)
  • (modified) llvm/test/TableGen/trydecode-emission3.td (+2-2)
  • (modified) llvm/test/TableGen/trydecode-emission4.td (+2-2)
  • (modified) llvm/utils/TableGen/DecoderEmitter.cpp (+1-16)
diff --git a/llvm/include/llvm/MC/MCDecoderOps.h b/llvm/include/llvm/MC/MCDecoderOps.h
index dea5b6931250f..d2e7cbf27b04b 100644
--- a/llvm/include/llvm/MC/MCDecoderOps.h
+++ b/llvm/include/llvm/MC/MCDecoderOps.h
@@ -30,7 +30,6 @@ enum DecoderOps {
                             //               nts_t NumToSkip)
   OPC_TryDecodeOrFail,      // OPC_TryDecodeOrFail(uleb128 Opcode, uleb128 DIdx)
   OPC_SoftFail,             // OPC_SoftFail(uleb128 PMask, uleb128 NMask)
-  OPC_Fail                  // OPC_Fail()
 };
 
 } // namespace llvm::MCD
diff --git a/llvm/test/TableGen/FixedLenDecoderEmitter/additional-encoding.td b/llvm/test/TableGen/FixedLenDecoderEmitter/additional-encoding.td
index 192cb3c3f5858..503822c37371e 100644
--- a/llvm/test/TableGen/FixedLenDecoderEmitter/additional-encoding.td
+++ b/llvm/test/TableGen/FixedLenDecoderEmitter/additional-encoding.td
@@ -47,7 +47,6 @@ class I<dag out_ops, dag in_ops> : Instruction {
 // CHECK-NEXT: /* 59 */ MCD::OPC_CheckField, 6, 6, 0, 4, 0,          // Skip to: 69
 // CHECK-NEXT: /* 65 */ MCD::OPC_Decode, {{[0-9]+}}, 2, 0,           // Opcode: {{.*}}:NOP
 // CHECK-NEXT: /* 69 */ MCD::OPC_TryDecodeOrFail, {{[0-9]+}}, 2, 1,
-// CHECK-NEXT: /* 73 */ MCD::OPC_Fail,
 
 class SHIFT<bits<2> opc> : I<(outs), (ins ShAmtOp:$shamt)>, EncSHIFT<opc>;
 def SHIFT0 : SHIFT<0>;
diff --git a/llvm/test/TableGen/FixedLenDecoderEmitter/big-filter.td b/llvm/test/TableGen/FixedLenDecoderEmitter/big-filter.td
index e525b4e7219df..7e2cda1bae9ed 100644
--- a/llvm/test/TableGen/FixedLenDecoderEmitter/big-filter.td
+++ b/llvm/test/TableGen/FixedLenDecoderEmitter/big-filter.td
@@ -11,7 +11,7 @@ class I : Instruction {
 
 // Check that a 64-bit filter with all bits set does not confuse DecoderEmitter.
 //
-// CHECK-LABEL: static const uint8_t DecoderTable128[35] = {
+// CHECK-LABEL: static const uint8_t DecoderTable128[34] = {
 // CHECK-NEXT:    MCD::OPC_ExtractField, 0, 64,
 // CHECK-NEXT:    MCD::OPC_FilterValue, 1, 8, 0,
 // CHECK-NEXT:    MCD::OPC_CheckFieldOrFail, 127, 1, 1,
@@ -19,7 +19,6 @@ class I : Instruction {
 // CHECK-NEXT:    MCD::OPC_FilterValueOrFail, 255, 255, 255, 255, 255, 255, 255, 255, 255, 1,
 // CHECK-NEXT:    MCD::OPC_CheckFieldOrFail, 127, 1, 0,
 // CHECK-NEXT:    MCD::OPC_Decode, 186, 2, 0,
-// CHECK-NEXT:    MCD::OPC_Fail,
 // CHECK-NEXT:  };
 
 def I1 : I {
diff --git a/llvm/test/TableGen/HwModeEncodeDecode.td b/llvm/test/TableGen/HwModeEncodeDecode.td
index 991054f8a279f..a5cae61997bc5 100644
--- a/llvm/test/TableGen/HwModeEncodeDecode.td
+++ b/llvm/test/TableGen/HwModeEncodeDecode.td
@@ -70,10 +70,10 @@ def baz : Instruction {
 }
 }
 
-// DECODER-LABEL: DecoderTable_ModeA32[22] =
+// DECODER-LABEL: DecoderTable_ModeA32
 // DECODER-DAG: Opcode: fooTypeEncA:foo
 // DECODER-DAG: Opcode: bar
-// DECODER-LABEL: DecoderTable_ModeB32[30] =
+// DECODER-LABEL: DecoderTable_ModeB32
 // DECODER-DAG: Opcode: fooTypeEncB:foo
 // DECODER-DAG: Opcode: fooTypeEncA:baz
 // DECODER-DAG: Opcode: bar
diff --git a/llvm/test/TableGen/HwModeEncodeDecode2.td b/llvm/test/TableGen/HwModeEncodeDecode2.td
index a62d723837c8f..8e65fcfcb4a1b 100644
--- a/llvm/test/TableGen/HwModeEncodeDecode2.td
+++ b/llvm/test/TableGen/HwModeEncodeDecode2.td
@@ -93,26 +93,26 @@ let OutOperandList = (outs) in {
   }
 }
 
-// DECODER-LABEL: DecoderTable_ModeA32[22] =
+// DECODER-LABEL: DecoderTable_ModeA32
 // DECODER-DAG: Opcode: fooTypeEncA:foo
 // DECODER-DAG: Opcode: bar
-// DECODER-LABEL: DecoderTable_ModeB32[30] =
+// DECODER-LABEL: DecoderTable_ModeB32
 // DECODER-DAG: Opcode: fooTypeEncB:foo
 // DECODER-DAG: Opcode: fooTypeEncA:baz
 // DECODER-DAG: Opcode: bar
-// DECODER-LABEL: DecoderTableAlt_ModeA32[9] =
+// DECODER-LABEL: DecoderTableAlt_ModeA32
 // DECODER-DAG: Opcode: unrelated
-// DECODER-LABEL: DecoderTableAlt_ModeB32[9] =
+// DECODER-LABEL: DecoderTableAlt_ModeB32
 // DECODER-DAG: Opcode: unrelated
 
-// DECODER-SUPPRESS-LABEL: DecoderTable32[9] =
+// DECODER-SUPPRESS-LABEL: DecoderTable32
 // DECODER-SUPPRESS-DAG: Opcode: bar
-// DECODER-SUPPRESS-LABEL: DecoderTable_ModeA32[9] =
+// DECODER-SUPPRESS-LABEL: DecoderTable_ModeA32
 // DECODER-SUPPRESS-DAG: Opcode: fooTypeEncA:foo
 // DECODER-SUPPRESS-NOT: Opcode: bar
-// DECODER-SUPPRESS-LABEL: DecoderTable_ModeB32[22] =
+// DECODER-SUPPRESS-LABEL: DecoderTable_ModeB32
 // DECODER-SUPPRESS-DAG: Opcode: fooTypeEncB:foo
 // DECODER-SUPPRESS-DAG: Opcode: fooTypeEncA:baz
 // DECODER-SUPPRESS-NOT: Opcode: bar
-// DECODER-SUPPRESS-LABEL: DecoderTableAlt32[9] =
+// DECODER-SUPPRESS-LABEL: DecoderTableAlt32
 // DECODER-SUPPRESS-DAG: Opcode: unrelated
diff --git a/llvm/test/TableGen/HwModeEncodeDecode3.td b/llvm/test/TableGen/HwModeEncodeDecode3.td
index a7366949f4017..dbbf866f057e5 100644
--- a/llvm/test/TableGen/HwModeEncodeDecode3.td
+++ b/llvm/test/TableGen/HwModeEncodeDecode3.td
@@ -116,46 +116,46 @@ def unrelated: Instruction {
 // significant duplication of DecoderTables. The four tables ‘DecoderTableAlt32’,
 // ‘DecoderTableAlt_ModeA32’, ‘DecoderTableAlt_ModeB32’ and 'DecoderTable_ModeC32' are
 // exact duplicates and could effectively be merged into one.
-// DECODER-LABEL: DecoderTable32[9] =
+// DECODER-LABEL: DecoderTable32
 // DECODER-DAG: Opcode: bar
-// DECODER-LABEL: DecoderTable64[9] =
+// DECODER-LABEL: DecoderTable64
 // DECODER-DAG: Opcode: fooTypeEncDefault:foo
-// DECODER-LABEL: DecoderTable_ModeA32[22] =
+// DECODER-LABEL: DecoderTable_ModeA32
 // DECODER-DAG: Opcode: fooTypeEncA:foo
 // DECODER-DAG: Opcode: bar
-// DECODER-LABEL: DecoderTable_ModeB32[30] =
+// DECODER-LABEL: DecoderTable_ModeB32
 // DECODER-DAG: Opcode: fooTypeEncB:foo
 // DECODER-DAG: Opcode: fooTypeEncA:baz
 // DECODER-DAG: Opcode: bar
-// DECODER-LABEL: DecoderTable_ModeC32[22] =
+// DECODER-LABEL: DecoderTable_ModeC32
 // DECODER-DAG: Opcode: fooTypeEncC:foo
 // DECODER-DAG: Opcode: bar
-// DECODER-LABEL: DecoderTableAlt32[9] =
+// DECODER-LABEL: DecoderTableAlt32
 // DECODER-DAG: Opcode: unrelated
-// DECODER-LABEL: DecoderTableAlt_ModeA32[9] =
+// DECODER-LABEL: DecoderTableAlt_ModeA32
 // DECODER-DAG: Opcode: unrelated
-// DECODER-LABEL: DecoderTableAlt_ModeB32[9] =
+// DECODER-LABEL: DecoderTableAlt_ModeB32
 // DECODER-DAG: Opcode: unrelated
-// DECODER-LABEL: DecoderTableAlt_ModeC32[9] =
+// DECODER-LABEL: DecoderTableAlt_ModeC32
 // DECODER-DAG: Opcode: unrelated
 
 // Under the 'O1' optimization level, unnecessary duplicate tables will be eliminated,
 // reducing the four ‘Alt’ tables down to just one.
-// DECODER-SUPPRESS-O1-LABEL: DecoderTable32[9] =
+// DECODER-SUPPRESS-O1-LABEL: DecoderTable32
 // DECODER-SUPPRESS-O1-DAG: Opcode: bar
-// DECODER-SUPPRESS-O1-LABEL: DecoderTable64[9] =
+// DECODER-SUPPRESS-O1-LABEL: DecoderTable64
 // DECODER-SUPPRESS-O1-DAG: Opcode: fooTypeEncDefault:foo
-// DECODER-SUPPRESS-O1-LABEL: DecoderTable_ModeA32[22] =
+// DECODER-SUPPRESS-O1-LABEL: DecoderTable_ModeA32
 // DECODER-SUPPRESS-O1-DAG: Opcode: fooTypeEncA:foo
 // DECODER-SUPPRESS-O1-DAG: Opcode: bar
-// DECODER-SUPPRESS-O1-LABEL: DecoderTable_ModeB32[30] =
+// DECODER-SUPPRESS-O1-LABEL: DecoderTable_ModeB32
 // DECODER-SUPPRESS-O1-DAG: Opcode: fooTypeEncB:foo
 // DECODER-SUPPRESS-O1-DAG: Opcode: fooTypeEncA:baz
 // DECODER-SUPPRESS-O1-DAG: Opcode: bar
-// DECODER-SUPPRESS-O1-LABEL: DecoderTable_ModeC32[22] =
+// DECODER-SUPPRESS-O1-LABEL: DecoderTable_ModeC32
 // DECODER-SUPPRESS-O1-DAG: Opcode: fooTypeEncC:foo
 // DECODER-SUPPRESS-O1-DAG: Opcode: bar
-// DECODER-SUPPRESS-O1-LABEL: DecoderTableAlt32[9] =
+// DECODER-SUPPRESS-O1-LABEL: DecoderTableAlt32
 // DECODER-SUPPRESS-O1-DAG: Opcode: unrelated
 
 // Under the 'O2' optimization condition, instructions possessing the 'EncodingByHwMode'
@@ -164,22 +164,22 @@ def unrelated: Instruction {
 // attribute but are within the same DecoderNamespace will be stored in the 'Default' table. This
 // approach will significantly reduce instruction redundancy, but it necessitates users to thoroughly
 // consider the interplay between HwMode and DecoderNamespace for their instructions.
-// DECODER-SUPPRESS-O2-LABEL: DecoderTable32[9] =
+// DECODER-SUPPRESS-O2-LABEL: DecoderTable32
 // DECODER-SUPPRESS-O2-DAG: Opcode: bar
-// DECODER-SUPPRESS-O2-LABEL: DecoderTable64[9] =
+// DECODER-SUPPRESS-O2-LABEL: DecoderTable64
 // DECODER-SUPPRESS-O2-NOT: Opcode: bar
 // DECODER-SUPPRESS-O2-DAG: Opcode: fooTypeEncDefault:foo
-// DECODER-SUPPRESS-O2-LABEL: DecoderTable_ModeA32[9] =
+// DECODER-SUPPRESS-O2-LABEL: DecoderTable_ModeA32
 // DECODER-SUPPRESS-O2-DAG: Opcode: fooTypeEncA:foo
 // DECODER-SUPPRESS-O2-NOT: Opcode: bar
-// DECODER-SUPPRESS-O2-LABEL: DecoderTable_ModeB32[22] =
+// DECODER-SUPPRESS-O2-LABEL: DecoderTable_ModeB32
 // DECODER-SUPPRESS-O2-DAG: Opcode: fooTypeEncB:foo
 // DECODER-SUPPRESS-O2-DAG: Opcode: fooTypeEncA:baz
 // DECODER-SUPPRESS-O2-NOT: Opcode: bar
-// DECODER-SUPPRESS-O2-LABEL: DecoderTable_ModeC32[13] =
+// DECODER-SUPPRESS-O2-LABEL: DecoderTable_ModeC32
 // DECODER-SUPPRESS-O2-DAG: Opcode: fooTypeEncC:foo
 // DECODER-SUPPRESS-O2-NOT: Opcode: bar
-// DECODER-SUPPRESS-O2-LABEL: DecoderTableAlt32[9] =
+// DECODER-SUPPRESS-O2-LABEL: DecoderTableAlt32
 // DECODER-SUPPRESS-O2-DAG: Opcode: unrelated
 
 // For 'bar' and 'unrelated', we didn't assign any HwModes for them,
diff --git a/llvm/test/TableGen/VarLenDecoder.td b/llvm/test/TableGen/VarLenDecoder.td
index 06ff62294a196..769c5895ec3c1 100644
--- a/llvm/test/TableGen/VarLenDecoder.td
+++ b/llvm/test/TableGen/VarLenDecoder.td
@@ -52,14 +52,14 @@ def FOO32 : MyVarInst<MemOp32> {
 // CHECK-SMALL-NEXT: /* 7 */       MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 0, // Opcode: FOO16
 // CHECK-SMALL-NEXT: /* 11 */      MCD::OPC_FilterValueOrFail, 9,
 // CHECK-SMALL-NEXT: /* 13 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: FOO32
-// CHECK-SMALL-NEXT: /* 17 */      MCD::OPC_Fail,
+// CHECK-SMALL-NEXT: };
 
 // CHECK-LARGE:      /* 0 */       MCD::OPC_ExtractField, 3, 5,  // Inst{7-3} ...
 // CHECK-LARGE-NEXT: /* 3 */       MCD::OPC_FilterValue, 8, 4, 0, 0, // Skip to: 12
 // CHECK-LARGE-NEXT: /* 8 */       MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 0, // Opcode: FOO16
 // CHECK-LARGE-NEXT: /* 12 */      MCD::OPC_FilterValueOrFail, 9,
 // CHECK-LARGE-NEXT: /* 14 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: FOO32
-// CHECK-LARGE-NEXT: /* 18 */      MCD::OPC_Fail,
+// CHECK-LARGE-NEXT: };
 
 // Instruction length table
 // CHECK: 27,
diff --git a/llvm/test/TableGen/trydecode-emission.td b/llvm/test/TableGen/trydecode-emission.td
index c3178dd71cf4b..6e47909b8f09a 100644
--- a/llvm/test/TableGen/trydecode-emission.td
+++ b/llvm/test/TableGen/trydecode-emission.td
@@ -39,7 +39,7 @@ def InstB : TestInstruction {
 // CHECK-NEXT: /* 5 */       MCD::OPC_CheckField, 2, 2, 0, 6, 0, // Skip to: 17
 // CHECK-NEXT: /* 11 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 17
 // CHECK-NEXT: /* 17 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA, DecodeIdx: {{[0-9]+}}
-// CHECK-NEXT: /* 21 */      MCD::OPC_Fail,
+// CHECK-NEXT: };
 
 // CHECK: if (!Check(S, DecodeInstB(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
 
@@ -52,7 +52,7 @@ def InstB : TestInstruction {
 // CHECK-LARGE-NEXT: /* 5 */       MCD::OPC_CheckField, 2, 2, 0, 7, 0, 0, // Skip to: 19
 // CHECK-LARGE-NEXT: /* 12 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 19
 // CHECK-LARGE-NEXT: /* 19 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA, DecodeIdx: {{[0-9]+}}
-// CHECK-LARGE-NEXT: /* 23 */      MCD::OPC_Fail,
+// CHECK-LARGE-NEXT: };
 
 // CHECK-LARGE: if (!Check(S, DecodeInstB(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
 
diff --git a/llvm/test/TableGen/trydecode-emission2.td b/llvm/test/TableGen/trydecode-emission2.td
index 4c8a95eff5dd1..826b1715514f9 100644
--- a/llvm/test/TableGen/trydecode-emission2.td
+++ b/llvm/test/TableGen/trydecode-emission2.td
@@ -39,7 +39,7 @@ def InstB : TestInstruction {
 // CHECK-NEXT: /* 16 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 22
 // CHECK-NEXT: /* 22 */      MCD::OPC_CheckFieldOrFail, 3, 2, 0,
 // CHECK-NEXT: /* 26 */      MCD::OPC_TryDecodeOrFail, {{[0-9]+}}, {{[0-9]+}}, 1,
-// CHECK-NEXT: /* 30 */      MCD::OPC_Fail,
+// CHECK-NEXT: };
 
 // CHECK: if (!Check(S, DecodeInstB(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
 // CHECK: if (!Check(S, DecodeInstA(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
@@ -52,7 +52,7 @@ def InstB : TestInstruction {
 // CHECK-LARGE-NEXT: /* 17 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 24
 // CHECK-LARGE-NEXT: /* 24 */      MCD::OPC_CheckFieldOrFail, 3, 2, 0,
 // CHECK-LARGE-NEXT: /* 28 */      MCD::OPC_TryDecodeOrFail, {{[0-9]+}}, {{[0-9]+}}, 1,
-// CHECK-LARGE-NEXT: /* 32 */      MCD::OPC_Fail,
+// CHECK-LARGE-NEXT: };
 
 // CHECK-LARGE: if (!Check(S, DecodeInstB(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
 // CHECK-LARGE: if (!Check(S, DecodeInstA(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
diff --git a/llvm/test/TableGen/trydecode-emission3.td b/llvm/test/TableGen/trydecode-emission3.td
index f262bfab77c3b..039a37ba416f6 100644
--- a/llvm/test/TableGen/trydecode-emission3.td
+++ b/llvm/test/TableGen/trydecode-emission3.td
@@ -40,7 +40,7 @@ def InstB : TestInstruction {
 // CHECK-NEXT: /* 5 */       MCD::OPC_CheckField, 2, 2, 0, 6, 0, // Skip to: 17
 // CHECK-NEXT: /* 11 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 17
 // CHECK-NEXT: /* 17 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA
-// CHECK-NEXT: /* 21 */      MCD::OPC_Fail,
+// CHECK-NEXT: };
 
 // CHECK: if (!Check(S, DecodeInstBOp(MI, tmp, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
 
@@ -49,6 +49,6 @@ def InstB : TestInstruction {
 // CHECK-LARGE-NEXT: /* 5 */       MCD::OPC_CheckField, 2, 2, 0, 7, 0, 0, // Skip to: 19
 // CHECK-LARGE-NEXT: /* 12 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 19
 // CHECK-LARGE-NEXT: /* 19 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA, DecodeIdx: {{[0-9]+}}
-// CHECK-LARGE-NEXT: /* 23 */      MCD::OPC_Fail,
+// CHECK-LARGE-NEXT: };
 
 // CHECK-LARGE: if (!Check(S, DecodeInstBOp(MI, tmp, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
diff --git a/llvm/test/TableGen/trydecode-emission4.td b/llvm/test/TableGen/trydecode-emission4.td
index 2c63229c053a5..d00d17501f16f 100644
--- a/llvm/test/TableGen/trydecode-emission4.td
+++ b/llvm/test/TableGen/trydecode-emission4.td
@@ -38,7 +38,7 @@ def InstB : TestInstruction {
 // CHECK-NEXT: /* 6 */       MCD::OPC_CheckField, 248, 3, 2, 0, 6, 0, // Skip to: 19
 // CHECK-NEXT: /* 13 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 19
 // CHECK-NEXT: /* 19 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA, DecodeIdx: {{[0-9]+}}
-// CHECK-NEXT: /* 23 */      MCD::OPC_Fail,
+// CHECK-NEXT: };
 
 // CHECK: if (!Check(S, DecodeInstB(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
 
@@ -48,7 +48,7 @@ def InstB : TestInstruction {
 // CHECK-LARGE-NEXT: /* 6 */       MCD::OPC_CheckField, 248, 3, 2, 0, 7, 0, 0, // Skip to: 21
 // CHECK-LARGE-NEXT: /* 14 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 21
 // CHECK-LARGE-NEXT: /* 21 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA, DecodeIdx: {{[0-9]+}}
-// CHECK-LARGE-NEXT: /* 25 */      MCD::OPC_Fail,
+// CHECK-LARGE-NEXT: };
 
 // CHECK-LARGE: if (!Check(S, DecodeInstB(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
 
diff --git a/llvm/utils/TableGen/DecoderEmitter.cpp b/llvm/utils/TableGen/DecoderEmitter.cpp
index 4f6eeb3922f9a..34ad78f72db13 100644
--- a/llvm/utils/TableGen/DecoderEmitter.cpp
+++ b/llvm/utils/TableGen/DecoderEmitter.cpp
@@ -312,7 +312,7 @@ struct DecoderTableInfo {
   PredicateSet Predicates;
   DecoderSet Decoders;
 
-  bool isOutermostScope() const { return FixupStack.size() == 1; }
+  bool isOutermostScope() const { return FixupStack.empty(); }
 
   void pushScope() { FixupStack.emplace_back(); }
 
@@ -770,8 +770,6 @@ unsigned DecoderEmitter::emitTable(formatted_raw_ostream &OS,
     uint32_t Index = ((I - Table.begin()) + NumToSkip);
     OS << (InComment ? ", " : "// ");
     OS << "Skip to: " << Index;
-    if (*(I + NumToSkip) == MCD::OPC_Fail)
-      OS << " (Fail)";
   };
 
   unsigned OpcodeMask = 0;
@@ -910,9 +908,6 @@ unsigned DecoderEmitter::emitTable(formatted_raw_ostream &OS,
       OS << '\n';
       break;
     }
-    case MCD::OPC_Fail:
-      OS << "  MCD::OPC_Fail,\n";
-      break;
     }
   }
   OS << "};\n\n";
@@ -2327,10 +2322,6 @@ static DecodeStatus decodeInstruction(const uint8_t DecodeTable[], MCInst &MI,
     })";
   }
   OS << R"(
-    case MCD::OPC_Fail: {
-      LLVM_DEBUG(dbgs() << Loc << ": OPC_Fail\n");
-      return MCDisassembler::Fail;
-    }
     }
   }
   llvm_unreachable("bogosity detected in disassembler state machine!");
@@ -2566,14 +2557,8 @@ namespace {
     // predicates and decoders themselves, however, are shared across all
     // decoders to give more opportunities for uniqueing.
     TableInfo.Table.clear();
-    TableInfo.pushScope();
     FC.emitTableEntries(TableInfo);
-    // Any NumToSkip fixups in the top level scope can resolve to the
-    // OPC_Fail at the end of the table.
     assert(TableInfo.isOutermostScope() && "fixup stack phasing error!");
-    TableInfo.popScope();
-
-    TableInfo.Table.insertOpcode(MCD::OPC_Fail);
 
     // Print the table to the output stream.
     OpcodeMask |= emitTable(OS, TableInfo.Table, DecoderNamespace, HwModeID,

jurahul
jurahul approved these changes Aug 25, 2025
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LGTM. I left the OPC_Fail when I added the OrFail variants in case there was a path in the code that escaped this check (to generate OrFail variant), but yeah, looks like there is none. Thanks for cleaning this up.

@s-barannikov s-barannikov merged commit 2a586a8 into llvm:main Aug 25, 2025
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@s-barannikov s-barannikov deleted the tablegen/decoder/remove-opc-fail branch August 25, 2025 16:15
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llvm:mc Machine (object) code tablegen

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@s-barannikov @llvmbot @jurahul