[llvm] Revert "[LLVM][TableGen] Parameterize NumToSkip in DecoderEmitter" (PR #136017)
Rahul Joshi via llvm-commits
llvm-commits at lists.llvm.org
Wed Apr 16 13:16:15 PDT 2025
https://github.com/jurahul created https://github.com/llvm/llvm-project/pull/136017
Reverts llvm/llvm-project#135882
Causing assert failures for AArch64 backend
>From 24b0bd6a97ed115c7530f0538eed9b9ef2b581f9 Mon Sep 17 00:00:00 2001
From: Rahul Joshi <rjoshi at nvidia.com>
Date: Wed, 16 Apr 2025 13:15:51 -0700
Subject: [PATCH] Revert "[LLVM][TableGen] Parameterize NumToSkip in
DecoderEmitter (#135882)"
This reverts commit 598ec8ce2d1e5e20b45c56de8972f58a0caeb697.
---
llvm/lib/Target/AArch64/CMakeLists.txt | 2 +-
llvm/test/TableGen/VarLenDecoder.td | 4 +-
llvm/test/TableGen/trydecode-emission.td | 10 +-
llvm/test/TableGen/trydecode-emission2.td | 16 +--
llvm/test/TableGen/trydecode-emission3.td | 2 +-
llvm/test/TableGen/trydecode-emission4.td | 2 +-
llvm/utils/TableGen/DecoderEmitter.cpp | 115 ++++++++++------------
7 files changed, 68 insertions(+), 83 deletions(-)
diff --git a/llvm/lib/Target/AArch64/CMakeLists.txt b/llvm/lib/Target/AArch64/CMakeLists.txt
index ba1d1605ec104..2300e479bc110 100644
--- a/llvm/lib/Target/AArch64/CMakeLists.txt
+++ b/llvm/lib/Target/AArch64/CMakeLists.txt
@@ -7,7 +7,7 @@ tablegen(LLVM AArch64GenAsmWriter.inc -gen-asm-writer)
tablegen(LLVM AArch64GenAsmWriter1.inc -gen-asm-writer -asmwriternum=1)
tablegen(LLVM AArch64GenCallingConv.inc -gen-callingconv)
tablegen(LLVM AArch64GenDAGISel.inc -gen-dag-isel)
-tablegen(LLVM AArch64GenDisassemblerTables.inc -gen-disassembler --num-to-skip-size=3)
+tablegen(LLVM AArch64GenDisassemblerTables.inc -gen-disassembler)
tablegen(LLVM AArch64GenFastISel.inc -gen-fast-isel)
tablegen(LLVM AArch64GenGlobalISel.inc -gen-global-isel)
tablegen(LLVM AArch64GenO0PreLegalizeGICombiner.inc -gen-global-isel-combiner
diff --git a/llvm/test/TableGen/VarLenDecoder.td b/llvm/test/TableGen/VarLenDecoder.td
index b77702ff7c5c1..5cf0bf8911859 100644
--- a/llvm/test/TableGen/VarLenDecoder.td
+++ b/llvm/test/TableGen/VarLenDecoder.td
@@ -47,9 +47,9 @@ def FOO32 : MyVarInst<MemOp32> {
}
// CHECK: MCD::OPC_ExtractField, 3, 5, // Inst{7-3} ...
-// CHECK-NEXT: MCD::OPC_FilterValue, 8, 4, 0, // Skip to: 11
+// CHECK-NEXT: MCD::OPC_FilterValue, 8, 4, 0, 0, // Skip to: 12
// CHECK-NEXT: MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 0, // Opcode: FOO16
-// CHECK-NEXT: MCD::OPC_FilterValue, 9, 4, 0, // Skip to: 19
+// CHECK-NEXT: MCD::OPC_FilterValue, 9, 4, 0, 0, // Skip to: 21
// CHECK-NEXT: MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: FOO32
// CHECK-NEXT: MCD::OPC_Fail,
diff --git a/llvm/test/TableGen/trydecode-emission.td b/llvm/test/TableGen/trydecode-emission.td
index 2b4239f4fbe65..20d2446eeac7f 100644
--- a/llvm/test/TableGen/trydecode-emission.td
+++ b/llvm/test/TableGen/trydecode-emission.td
@@ -34,10 +34,10 @@ def InstB : TestInstruction {
}
// CHECK: /* 0 */ MCD::OPC_ExtractField, 4, 4, // Inst{7-4} ...
-// CHECK-NEXT: /* 3 */ MCD::OPC_FilterValue, 0, 16, 0, // Skip to: 23
-// CHECK-NEXT: /* 7 */ MCD::OPC_CheckField, 2, 2, 0, 6, 0, // Skip to: 19
-// CHECK-NEXT: /* 13 */ MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, skip to: 19
-// CHECK-NEXT: /* 19 */ MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA
-// CHECK-NEXT: /* 23 */ MCD::OPC_Fail,
+// CHECK-NEXT: /* 3 */ MCD::OPC_FilterValue, 0, 18, 0, 0, // Skip to: 26
+// CHECK-NEXT: /* 8 */ MCD::OPC_CheckField, 2, 2, 0, 7, 0, 0, // Skip to: 22
+// CHECK-NEXT: /* 15 */ MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, skip to: 22
+// CHECK-NEXT: /* 22 */ MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA
+// CHECK-NEXT: /* 26 */ MCD::OPC_Fail,
// CHECK: 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 7d30474058f73..0584034e41233 100644
--- a/llvm/test/TableGen/trydecode-emission2.td
+++ b/llvm/test/TableGen/trydecode-emission2.td
@@ -31,14 +31,14 @@ def InstB : TestInstruction {
}
// CHECK: /* 0 */ MCD::OPC_ExtractField, 2, 1, // Inst{2} ...
-// CHECK-NEXT: /* 3 */ MCD::OPC_FilterValue, 0, 31, 0, // Skip to: 38
-// CHECK-NEXT: /* 7 */ MCD::OPC_ExtractField, 5, 3, // Inst{7-5} ...
-// CHECK-NEXT: /* 10 */ MCD::OPC_FilterValue, 0, 24, 0, // Skip to: 38
-// CHECK-NEXT: /* 14 */ MCD::OPC_CheckField, 0, 2, 3, 6, 0, // Skip to: 26
-// CHECK-NEXT: /* 20 */ MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, skip to: 26
-// CHECK-NEXT: /* 26 */ MCD::OPC_CheckField, 3, 2, 0, 6, 0, // Skip to: 38
-// CHECK-NEXT: /* 32 */ MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 1, 0, 0, // Opcode: InstA, skip to: 38
-// CHECK-NEXT: /* 38 */ MCD::OPC_Fail,
+// CHECK-NEXT: /* 3 */ MCD::OPC_FilterValue, 0, 36, 0, 0, // Skip to: 44
+// CHECK-NEXT: /* 8 */ MCD::OPC_ExtractField, 5, 3, // Inst{7-5} ...
+// CHECK-NEXT: /* 11 */ MCD::OPC_FilterValue, 0, 28, 0, 0, // Skip to: 44
+// CHECK-NEXT: /* 16 */ MCD::OPC_CheckField, 0, 2, 3, 7, 0, 0, // Skip to: 30
+// CHECK-NEXT: /* 23 */ MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, skip to: 30
+// CHECK-NEXT: /* 30 */ MCD::OPC_CheckField, 3, 2, 0, 7, 0, 0, // Skip to: 44
+// CHECK-NEXT: /* 37 */ MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 1, 0, 0, 0, // Opcode: InstA, skip to: 44
+// CHECK-NEXT: /* 44 */ MCD::OPC_Fail,
// 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; }
diff --git a/llvm/test/TableGen/trydecode-emission3.td b/llvm/test/TableGen/trydecode-emission3.td
index 0abbe62fe337e..4c5be7e1af229 100644
--- a/llvm/test/TableGen/trydecode-emission3.td
+++ b/llvm/test/TableGen/trydecode-emission3.td
@@ -1,4 +1,4 @@
- // RUN: llvm-tblgen -gen-disassembler --num-to-skip-size=3 -I %p/../../include %s | FileCheck %s
+// RUN: llvm-tblgen -gen-disassembler -I %p/../../include %s | FileCheck %s
include "llvm/Target/Target.td"
diff --git a/llvm/test/TableGen/trydecode-emission4.td b/llvm/test/TableGen/trydecode-emission4.td
index 413e4a0d1275a..1e51ba5e40768 100644
--- a/llvm/test/TableGen/trydecode-emission4.td
+++ b/llvm/test/TableGen/trydecode-emission4.td
@@ -1,4 +1,4 @@
-// RUN: llvm-tblgen -gen-disassembler --num-to-skip-size=3 -I %p/../../include %s | FileCheck %s
+// RUN: llvm-tblgen -gen-disassembler -I %p/../../include %s | FileCheck %s
// Test for OPC_ExtractField/OPC_CheckField with start bit > 255.
// These large start values may arise for architectures with long instruction
diff --git a/llvm/utils/TableGen/DecoderEmitter.cpp b/llvm/utils/TableGen/DecoderEmitter.cpp
index 0735702abf339..9c6015cc24576 100644
--- a/llvm/utils/TableGen/DecoderEmitter.cpp
+++ b/llvm/utils/TableGen/DecoderEmitter.cpp
@@ -32,10 +32,8 @@
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
-#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/FormattedStream.h"
#include "llvm/Support/LEB128.h"
-#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/TableGen/Error.h"
#include "llvm/TableGen/Record.h"
@@ -78,12 +76,6 @@ static cl::opt<SuppressLevel> DecoderEmitterSuppressDuplicates(
"significantly reducing Table Duplications")),
cl::init(SUPPRESSION_DISABLE), cl::cat(DisassemblerEmitterCat));
-static cl::opt<uint32_t>
- NumToSkipSizeInBytes("num-to-skip-size",
- cl::desc("number of bytes to use for num-to-skip "
- "entries in the decoder table (2 or 3)"),
- cl::init(2), cl::cat(DisassemblerEmitterCat));
-
STATISTIC(NumEncodings, "Number of encodings considered");
STATISTIC(NumEncodingsLackingDisasm,
"Number of encodings without disassembler info");
@@ -138,29 +130,10 @@ struct DecoderTable : public std::vector<uint8_t> {
// in the table for patching.
size_t insertNumToSkip() {
size_t Size = size();
- insert(end(), NumToSkipSizeInBytes, 0);
+ insert(end(), 3, 0);
return Size;
}
-
- void patchNumToSkip(size_t FixupIdx, uint32_t DestIdx) {
- // Calculate the distance from the byte following the fixup entry byte
- // to the destination. The Target is calculated from after the
- // `NumToSkipSizeInBytes`-byte NumToSkip entry itself, so subtract
- // `NumToSkipSizeInBytes` from the displacement here to account for that.
- assert(DestIdx > FixupIdx + NumToSkipSizeInBytes &&
- "Expecting a forward jump in the decoding table");
- uint32_t Delta = DestIdx - FixupIdx - NumToSkipSizeInBytes;
- if (!isUIntN(8 * NumToSkipSizeInBytes, Delta))
- PrintFatalError(
- "disassembler decoding table too large, try --num-to-skip-size=3");
-
- (*this)[FixupIdx] = static_cast<uint8_t>(Delta);
- (*this)[FixupIdx + 1] = static_cast<uint8_t>(Delta >> 8);
- if (NumToSkipSizeInBytes == 3)
- (*this)[FixupIdx + 2] = static_cast<uint8_t>(Delta >> 16);
- }
};
-
struct DecoderTableInfo {
DecoderTable Table;
FixupScopeList FixupStack;
@@ -717,8 +690,19 @@ static void resolveTableFixups(DecoderTable &Table, const FixupList &Fixups,
uint32_t DestIdx) {
// Any NumToSkip fixups in the current scope can resolve to the
// current location.
- for (uint32_t FixupIdx : Fixups)
- Table.patchNumToSkip(FixupIdx, DestIdx);
+ for (uint32_t FixupIdx : reverse(Fixups)) {
+ // Calculate the distance from the byte following the fixup entry byte
+ // to the destination. The Target is calculated from after the 24-bit
+ // NumToSkip entry itself, so subtract three from the displacement here
+ // to account for that.
+ uint32_t Delta = DestIdx - FixupIdx - 3;
+ // Our NumToSkip entries are 24-bits. Make sure our table isn't too
+ // big.
+ assert(isUInt<24>(Delta));
+ Table[FixupIdx] = (uint8_t)Delta;
+ Table[FixupIdx + 1] = (uint8_t)(Delta >> 8);
+ Table[FixupIdx + 2] = (uint8_t)(Delta >> 16);
+ }
}
// Emit table entries to decode instructions given a segment or segments
@@ -775,9 +759,15 @@ void Filter::emitTableEntry(DecoderTableInfo &TableInfo) const {
Delegate->emitTableEntries(TableInfo);
// Now that we've emitted the body of the handler, update the NumToSkip
- // of the filter itself to be able to skip forward when false.
- if (PrevFilter)
- Table.patchNumToSkip(PrevFilter, Table.size());
+ // of the filter itself to be able to skip forward when false. Subtract
+ // three as to account for the width of the NumToSkip field itself.
+ if (PrevFilter) {
+ uint32_t NumToSkip = Table.size() - PrevFilter - 3;
+ assert(isUInt<24>(NumToSkip) && "disassembler decoding table too large!");
+ Table[PrevFilter] = (uint8_t)NumToSkip;
+ Table[PrevFilter + 1] = (uint8_t)(NumToSkip >> 8);
+ Table[PrevFilter + 2] = (uint8_t)(NumToSkip >> 16);
+ }
}
// If there is no fallthrough, then the final filter should get fixed
@@ -824,8 +814,7 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
OS << (unsigned)*I++ << ", ";
};
- // Emit `NumToSkipSizeInBytes`-byte numtoskip value to OS, returning the
- // NumToSkip value.
+ // Emit 24-bit numtoskip value to OS, returning the NumToSkip value.
auto emitNumToSkip = [](DecoderTable::const_iterator &I,
formatted_raw_ostream &OS) {
uint8_t Byte = *I++;
@@ -834,11 +823,9 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
Byte = *I++;
OS << (unsigned)Byte << ", ";
NumToSkip |= Byte << 8;
- if (NumToSkipSizeInBytes == 3) {
- Byte = *I++;
- OS << (unsigned)(Byte) << ", ";
- NumToSkip |= Byte << 16;
- }
+ Byte = *I++;
+ OS << (unsigned)(Byte) << ", ";
+ NumToSkip |= Byte << 16;
return NumToSkip;
};
@@ -880,7 +867,7 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
// The filter value is ULEB128 encoded.
emitULEB128(I, OS);
- // numtoskip value.
+ // 24-bit numtoskip value.
uint32_t NumToSkip = emitNumToSkip(I, OS);
OS << "// Skip to: " << ((I - Table.begin()) + NumToSkip) << "\n";
break;
@@ -896,7 +883,7 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
// ULEB128 encoded field value.
emitULEB128(I, OS);
- // numtoskip value.
+ // 24-bit numtoskip value.
uint32_t NumToSkip = emitNumToSkip(I, OS);
OS << "// Skip to: " << ((I - Table.begin()) + NumToSkip) << "\n";
break;
@@ -906,7 +893,7 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
OS << Indent << "MCD::OPC_CheckPredicate, ";
emitULEB128(I, OS);
- // numtoskip value.
+ // 24-bit numtoskip value.
uint32_t NumToSkip = emitNumToSkip(I, OS);
OS << "// Skip to: " << ((I - Table.begin()) + NumToSkip) << "\n";
break;
@@ -938,7 +925,7 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
// Fallthrough for OPC_TryDecode.
- // numtoskip value.
+ // 24-bit numtoskip value.
uint32_t NumToSkip = emitNumToSkip(I, OS);
OS << "// Opcode: " << NumberedEncodings[EncodingID]
@@ -1424,9 +1411,9 @@ void FilterChooser::emitSingletonTableEntry(DecoderTableInfo &TableInfo,
TableInfo.Table.push_back(NumBits);
TableInfo.Table.insertULEB128(Ilnd.FieldVal);
- // Allocate space in the table for fixup (NumToSkipSizeInBytes) so all
- // our relative position calculations work OK even before we fully
- // resolve the real value here.
+ // The fixup is always 24-bits, so go ahead and allocate the space
+ // in the table so all our relative position calculations work OK even
+ // before we fully resolve the real value here.
// Push location for NumToSkip backpatching.
TableInfo.FixupStack.back().push_back(TableInfo.Table.insertNumToSkip());
@@ -2170,18 +2157,7 @@ insertBits(InsnType &field, uint64_t bits, unsigned startBit, unsigned numBits)
// decodeInstruction().
static void emitDecodeInstruction(formatted_raw_ostream &OS,
bool IsVarLenInst) {
- OS << formatv("\nconstexpr unsigned NumToSkipSizeInBytes = {};\n",
- NumToSkipSizeInBytes);
-
OS << R"(
-inline unsigned decodeNumToSkip(const uint8_t *&Ptr) {
- unsigned NumToSkip = *Ptr++;
- NumToSkip |= (*Ptr++) << 8;
- if constexpr (NumToSkipSizeInBytes == 3)
- NumToSkip |= (*Ptr++) << 16;
- return NumToSkip;
-}
-
template <typename InsnType>
static DecodeStatus decodeInstruction(const uint8_t DecodeTable[], MCInst &MI,
InsnType insn, uint64_t Address,
@@ -2219,7 +2195,10 @@ static DecodeStatus decodeInstruction(const uint8_t DecodeTable[], MCInst &MI,
// Decode the field value.
uint64_t Val = decodeULEB128AndIncUnsafe(++Ptr);
bool Failed = Val != CurFieldValue;
- unsigned NumToSkip = decodeNumToSkip(Ptr);
+ // NumToSkip is a plain 24-bit integer.
+ unsigned NumToSkip = *Ptr++;
+ NumToSkip |= (*Ptr++) << 8;
+ NumToSkip |= (*Ptr++) << 16;
// Perform the filter operation.
if (Failed)
@@ -2243,7 +2222,10 @@ static DecodeStatus decodeInstruction(const uint8_t DecodeTable[], MCInst &MI,
uint64_t ExpectedValue = decodeULEB128(++Ptr, &PtrLen);
Ptr += PtrLen;
bool Failed = ExpectedValue != FieldValue;
- unsigned NumToSkip = decodeNumToSkip(Ptr);
+ // NumToSkip is a plain 24-bit integer.
+ unsigned NumToSkip = *Ptr++;
+ NumToSkip |= (*Ptr++) << 8;
+ NumToSkip |= (*Ptr++) << 16;
// If the actual and expected values don't match, skip.
if (Failed)
@@ -2258,7 +2240,10 @@ static DecodeStatus decodeInstruction(const uint8_t DecodeTable[], MCInst &MI,
case MCD::OPC_CheckPredicate: {
// Decode the Predicate Index value.
unsigned PIdx = decodeULEB128AndIncUnsafe(++Ptr);
- unsigned NumToSkip = decodeNumToSkip(Ptr);
+ // NumToSkip is a plain 24-bit integer.
+ unsigned NumToSkip = *Ptr++;
+ NumToSkip |= (*Ptr++) << 8;
+ NumToSkip |= (*Ptr++) << 16;
// Check the predicate.
bool Failed = !checkDecoderPredicate(PIdx, Bits);
if (Failed)
@@ -2293,7 +2278,10 @@ static DecodeStatus decodeInstruction(const uint8_t DecodeTable[], MCInst &MI,
// Decode the Opcode value.
unsigned Opc = decodeULEB128AndIncUnsafe(++Ptr);
unsigned DecodeIdx = decodeULEB128AndIncUnsafe(Ptr);
- unsigned NumToSkip = decodeNumToSkip(Ptr);
+ // NumToSkip is a plain 24-bit integer.
+ unsigned NumToSkip = *Ptr++;
+ NumToSkip |= (*Ptr++) << 8;
+ NumToSkip |= (*Ptr++) << 16;
// Perform the decode operation.
MCInst TmpMI;
@@ -2418,9 +2406,6 @@ handleHwModesUnrelatedEncodings(const CodeGenInstruction *Instr,
// Emits disassembler code for instruction decoding.
void DecoderEmitter::run(raw_ostream &o) {
- if (NumToSkipSizeInBytes != 2 && NumToSkipSizeInBytes != 3)
- PrintFatalError("Invalid value for num-to-skip-size, must be 2 or 3");
-
formatted_raw_ostream OS(o);
OS << R"(
#include "llvm/MC/MCInst.h"
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