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[RISCV] Implement Xqci Call Relaxations #201

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Merged
quic-seaswara merged 1 commit into from
Aug 1, 2025
Merged

[RISCV] Implement Xqci Call Relaxations #201

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143 changes: 86 additions & 57 deletions lib/Target/RISCV/RISCVLDBackend.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -222,11 +222,23 @@ void RISCVLDBackend::reportMissedRelaxation(StringRef Name,
recordRelaxationStats(Section, 0, NumBytes);
}

bool RISCVLDBackend::doRelaxationCall(Relocation *reloc, bool DoCompressed) {
bool RISCVLDBackend::doRelaxationCall(Relocation *reloc) {
/* Three similar relaxations can be applied here, in order of preference:
* -- auipc;jalr -> c.j/c.jal (saves 6 bytes)
* -- auipc;jalr -> jal (saves 4 bytes)
* -- auipc;jalr -> qc.e.j/qc.e.jal (saves 2 bytes) (Xqci only)
*/

Fragment *frag = reloc->targetRef()->frag();
RegionFragmentEx *region = llvm::dyn_cast<RegionFragmentEx>(frag);
if (!region)
return true;

Relocator::DWord S = getSymbolValuePLT(*reloc);
Relocator::DWord A = reloc->addend();
Relocator::DWord P = reloc->place(m_Module);
Relocator::DWord X = S + A - P;

uint64_t offset = reloc->targetRef()->offset();

// extract the next instruction
Expand All @@ -238,68 +250,87 @@ bool RISCVLDBackend::doRelaxationCall(Relocation *reloc, bool DoCompressed) {
return false;

unsigned rd = (jalr_instr >> 7) & 0x1fu;
bool canCompress = (rd == 0 || (rd == 1 && config().targets().is32Bits()));

// test if it can fall into 21bits
Relocator::DWord S = getSymbolValuePLT(*reloc);
Relocator::DWord A = reloc->addend();
Relocator::DWord P = reloc->place(m_Module);
Relocator::DWord X = S + A - P;
bool canRelax = config().options().getRISCVRelax() && llvm::isInt<21>(X);
// For `C.J`/`C.JAL`, we have to have C relaxations enabled,
// and be within 12 bits, and have a destination of `x0` or `ra`
bool canRelaxCJ = config().options().getRISCVRelax() &&
config().options().getRISCVRelaxToC() && isInt<12>(X) &&
(rd == 0 || (rd == 1 && config().targets().is32Bits()));

if (!canRelax) {
reportMissedRelaxation("RISCV_CALL", *region, offset, canCompress ? 6 : 4,
reloc->symInfo()->name());
return false;
// For `JAL`, the offset needs to be 21 bits.
bool canRelaxJal = config().options().getRISCVRelax() && llvm::isInt<21>(X);

// For `QC.E.J` and `QC.E.JAL`, we have to have xqci relaxations enabled,
// and be on 32-bit, and the destination must be either `x0` or `ra`.
bool canRelaxXqci = config().options().getRISCVRelax() &&
config().targets().is32Bits() &&
config().options().getRISCVRelaxXqci();
bool canRelaxQcEJ = canRelaxXqci && (rd == 0 || rd == 1);

const char *msgC = (rd == 1) ? "RISCV_CALL_JAL" : "RISCV_CALL_J";
if (canRelaxCJ) {
uint16_t c_j = (rd == 1) ? 0x2001u : 0xa001;

if (m_Module.getPrinter()->isVerbose())
config().raise(Diag::relax_to_compress)
<< msgC
<< llvm::utohexstr(reloc->target(), true, 8) + "," +
llvm::utohexstr(jalr_instr, true, 8)
<< llvm::utohexstr(c_j, true, 4) << reloc->symInfo()->name()
<< region->getOwningSection()->name() << llvm::utohexstr(offset)
<< region->getOwningSection()
->getInputFile()
->getInput()
->decoratedPath();

region->replaceInstruction(offset, reloc, c_j, 2);
reloc->setTargetData(c_j);
reloc->setType(llvm::ELF::R_RISCV_RVC_JUMP);
relaxDeleteBytes("RISCV_CALL_C", *region, offset + 2, 6,
reloc->symInfo()->name());

return true;
}

// Test if we can use C.JAL or C.J.
if (canCompress) {
bool canRelaxToCompressed = config().options().getRISCVRelax() &&
DoCompressed && llvm::isInt<12>(X);
if (canRelaxToCompressed) {
// C.J uses x0 as return register (writes are ignored)
// C.JAL uses x1 as return register (ABI link register)
uint32_t compressed = rd == 1 ? 0x2001 : 0xa001;
const char *msg = rd == 1 ? "RISCV_CALL_JAL" : "RISCV_CALL_J";
if (m_Module.getPrinter()->isVerbose())
config().raise(Diag::relax_to_compress)
<< msg
<< llvm::utohexstr(reloc->target(), true, 8) + "," +
llvm::utohexstr(jalr_instr, true, 8)
<< llvm::utohexstr(compressed, true, 4) << reloc->symInfo()->name()
<< region->getOwningSection()->name() << llvm::utohexstr(offset)
<< region->getOwningSection()
->getInputFile()
->getInput()
->decoratedPath();
if (canRelaxJal) {
// Replace the instruction to JAL
uint32_t jal = 0x6fu | rd << 7;

region->replaceInstruction(offset, reloc, compressed, 2);
// Replace the reloc to R_RISCV_RVC_JUMP
reloc->setType(llvm::ELF::R_RISCV_RVC_JUMP);
reloc->setTargetData(compressed);
// Delete the next instruction
relaxDeleteBytes("RISCV_CALL_C", *region, offset + 2, 6,
reloc->symInfo()->name());
return true;
}
region->replaceInstruction(offset, reloc, jal, 4 /* Replace bytes */);
reloc->setTargetData(jal);
reloc->setType(llvm::ELF::R_RISCV_JAL);
// Delete the next instruction
relaxDeleteBytes("RISCV_CALL", *region, offset + 4, 4,
reloc->symInfo()->name());

// Report missed relaxation as we could still do a `C.J`/`C.JAL`
reportMissedRelaxation("RISCV_CALL_C", *region, offset, 2,
reloc->symInfo()->name());

return true;
}

// Replace the instruction to JAL
uint32_t instr = 0x6fu | rd << 7;
region->replaceInstruction(offset, reloc, instr, 4 /* Replace bytes */);
// Replace the reloc to R_RISCV_JAL
reloc->setType(llvm::ELF::R_RISCV_JAL);
reloc->setTargetData(instr);
// Delete the next instruction
relaxDeleteBytes("RISCV_CALL", *region, offset + 4, 4,
reloc->symInfo()->name());
return true;
if (canRelaxQcEJ) {
uint64_t qc_e_j = (rd == 1) ? 0xc01ful : 0x401ful;
const char *msg =
(rd == 1) ? "R_RISCV_CALL_QC_E_JAL" : "R_RISCV_CALL_QC_E_J";

region->replaceInstruction(offset, reloc, qc_e_j, 6);
reloc->setTargetData(qc_e_j);
reloc->setType(ELF::riscv::internal::R_RISCV_QC_E_CALL_PLT);
relaxDeleteBytes(msg, *region, offset + 6, 2, reloc->symInfo()->name());

reportMissedRelaxation(msg, *region, offset, 4, reloc->symInfo()->name());

return true;
}

reportMissedRelaxation("RISCV_CALL", *region, offset, 6,
reloc->symInfo()->name());
return false;
}

bool RISCVLDBackend::doRelaxationQCCall(Relocation *reloc, bool DoCompressed) {
bool RISCVLDBackend::doRelaxationQCCall(Relocation *reloc) {
// This function performs the relaxation to replace: QC.E.JAL or QC.E.J with
// one of JAL, C.J, or C.JAL.

Expand All @@ -318,6 +349,7 @@ bool RISCVLDBackend::doRelaxationQCCall(Relocation *reloc, bool DoCompressed) {
Relocator::DWord P = reloc->place(m_Module);
Relocator::DWord X = S + A - P;

bool DoCompressed = config().options().getRISCVRelaxToC();
bool canRelaxXqci =
config().targets().is32Bits() && config().options().getRISCVRelaxXqci();
bool canRelax =
Expand Down Expand Up @@ -900,9 +932,6 @@ void RISCVLDBackend::mayBeRelax(int relaxation_pass, bool &pFinished) {
if (m_pGlobalPointer)
GP = m_pGlobalPointer->value();

// Compress
bool DoCompressed = config().options().getRISCVRelaxToC();

// start relocation relaxation
for (auto &input : m_Module.getObjectList()) {
ELFObjectFile *ObjFile = llvm::dyn_cast<ELFObjectFile>(input);
Expand Down Expand Up @@ -934,7 +963,7 @@ void RISCVLDBackend::mayBeRelax(int relaxation_pass, bool &pFinished) {
case llvm::ELF::R_RISCV_CALL:
case llvm::ELF::R_RISCV_CALL_PLT: {
if (nextRelax && relaxation_pass == RELAXATION_CALL)
doRelaxationCall(relocation, DoCompressed);
doRelaxationCall(relocation);
break;
}
case llvm::ELF::R_RISCV_PCREL_HI20:
Expand All @@ -959,7 +988,7 @@ void RISCVLDBackend::mayBeRelax(int relaxation_pass, bool &pFinished) {
}
case ELF::riscv::internal::R_RISCV_QC_E_CALL_PLT: {
if (nextRelax && relaxation_pass == RELAXATION_CALL)
doRelaxationQCCall(relocation, DoCompressed);
doRelaxationQCCall(relocation);
break;
}
case ELF::riscv::internal::R_RISCV_QC_E_32:
Expand Down
4 changes: 2 additions & 2 deletions lib/Target/RISCV/RISCVLDBackend.h
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Original file line number Diff line number Diff line change
Expand Up @@ -197,8 +197,8 @@ class RISCVLDBackend : public GNULDBackend {

bool isGOTReloc(Relocation *reloc) const;

bool doRelaxationCall(Relocation *R, bool DoCompressed);
bool doRelaxationQCCall(Relocation *R, bool DoCompressed);
bool doRelaxationCall(Relocation *R);
bool doRelaxationQCCall(Relocation *R);

bool doRelaxationLui(Relocation *R, Relocation::DWord G);
bool doRelaxationQCLi(Relocation *R, Relocation::DWord G);
Expand Down
2 changes: 1 addition & 1 deletion test/RISCV/standalone/Relaxation/AUIPC_JALR_TO_CJ/AUIPC_JALR_TO_CJ.test
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Expand Up @@ -22,8 +22,8 @@ VERBOSE_RELAX: RISCV_CALL_C : Deleting 6 bytes for symbol 'foo' in section .text
DUMP_RELAX: b011 j 0x{{[0-9a-f]+}} <foo>

## The third jump is never compressed because it's too far
VERBOSE_RELAX: RISCV_CALL_C : Cannot relax 2 bytes for symbol 'foo' in section .text+0xff6 file {{.*}}.o
VERBOSE_RELAX: RISCV_CALL : Deleting 4 bytes for symbol 'foo' in section .text+0xffa file {{.*}}.o
VERBOSE_RELAX: RISCV_CALL_C : Cannot relax 2 bytes for symbol 'foo' in section .text+0xff6 file {{.*}}.o
DUMP_RELAX: 80aff06f j 0x{{[0-9a-f]+}} <foo>

RUN: %link %linkopts %t.o -o %t.2.out --verbose --no-relax 2>&1 | %filecheck %s --check-prefix=VERBOSE_NORELAX
Expand Down
4 changes: 2 additions & 2 deletions test/RISCV/standalone/Relaxation/AUIPC_JALR_TO_JAL/AUIPC_JALR_TO_JAL_RV32.test
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Original file line number Diff line number Diff line change
Expand Up @@ -12,10 +12,10 @@ VERBOSE_RELAX_C: RISCV_CALL_JAL : relaxing instruction 0x00000097,000080e7 to co
VERBOSE_RELAX_C: RISCV_CALL_C : Deleting 6 bytes for symbol 'f' in section .text+0x4 file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL_JAL : relaxing instruction 0x00000097,000080e7 to compressed instruction 0x2001 for symbol f in section .text+0x77A file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL_C : Deleting 6 bytes for symbol 'f' in section .text+0x77c file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL_C : Cannot relax 2 bytes for symbol 'f' in section .text+0x874 file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL : Deleting 4 bytes for symbol 'f' in section .text+0x878 file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL_C : Cannot relax 2 bytes for symbol 'f' in section .text+0xffef0 file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL_C : Cannot relax 2 bytes for symbol 'f' in section .text+0x874 file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL : Deleting 4 bytes for symbol 'f' in section .text+0xffef4 file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL_C : Cannot relax 2 bytes for symbol 'f' in section .text+0xffef0 file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL : Cannot relax 6 bytes for symbol 'f' in section .text+0x1000ec file {{.*}}.o

RUN: %objdump -d %t.1.out 2>&1 | %filecheck %s --check-prefix=DUMP_RELAX_C
Expand Down
18 changes: 10 additions & 8 deletions test/RISCV/standalone/Relaxation/AUIPC_JALR_TO_JAL/AUIPC_JALR_TO_JAL_RV64.test
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ VERBOSE_RELAX_C: RISCV_CALL : Deleting 4 bytes for symbol 'f' in section .text+0
VERBOSE_RELAX_C: RISCV_CALL : Deleting 4 bytes for symbol 'f' in section .text+0x780 file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL : Deleting 4 bytes for symbol 'f' in section .text+0x87c file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL : Deleting 4 bytes for symbol 'f' in section .text+0xffef8 file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL : Cannot relax 4 bytes for symbol 'f' in section .text+0x1000f0 file {{.*}}.o
VERBOSE_RELAX_C: RISCV_CALL : Cannot relax 6 bytes for symbol 'f' in section .text+0x1000f0 file {{.*}}.o
VERBOSE_RELAX_C-NOT: Cannot relax

RUN: %objdump -d %t.1.out 2>&1 | %filecheck %s --check-prefix=DUMP_RELAX_C
Expand All @@ -26,35 +26,37 @@ DUMP_RELAX_C: f10080e7 jalr
RUN: %filecheck %s --input-file=%t.1.map --check-prefix=MAP_RELAX_C
MAP_RELAX_C: # LinkStats Begin
MAP_RELAX_C: # RelaxationBytesDeleted : 16
MAP_RELAX_C: # RelaxationBytesMissed : 4
MAP_RELAX_C: # RelaxationBytesMissed : 14
MAP_RELAX_C: # LinkStats End

MAP_RELAX_C: .text {{.+}}, Alignment: 0x2, Flags: SHF_ALLOC|SHF_EXECINSTR, Type: SHT_PROGBITS
MAP_RELAX_C: # RelaxationBytesDeleted : 16
MAP_RELAX_C: # RelaxationBytesMissed : 4
MAP_RELAX_C: # RelaxationBytesMissed : 14
MAP_RELAX_C: .text {{.+}}.o #SHT_PROGBITS,SHF_ALLOC|SHF_EXECINSTR,2

# Only non-compressed relaxations are enabled.
RUN: %link %linkopts --no-relax-c %t.o -o %t.2.out -MapStyle txt -Map %t.2.map --verbose 2>&1 | %filecheck %s --check-prefix=VERBOSE_RELAX
VERBOSE_RELAX: RISCV_CALL : Cannot relax 4 bytes for symbol 'f' in section .text+0x1000f0 file {{.*}}.o
VERBOSE_RELAX: RISCV_CALL : Cannot relax 6 bytes for symbol 'f' in section .text+0x1000f0 file {{.*}}.o

RUN: %filecheck %s --input-file=%t.2.map --check-prefix=MAP_RELAX
MAP_RELAX: # LinkStats Begin
MAP_RELAX: # RelaxationBytesMissed : 4
MAP_RELAX: # RelaxationBytesDeleted : 16
MAP_RELAX: # RelaxationBytesMissed : 14
MAP_RELAX: # LinkStats End

MAP_RELAX: .text {{.+}}, Alignment: 0x2, Flags: SHF_ALLOC|SHF_EXECINSTR, Type: SHT_PROGBITS
MAP_RELAX: # RelaxationBytesMissed : 4
MAP_RELAX: # RelaxationBytesDeleted : 16
MAP_RELAX: # RelaxationBytesMissed : 14
MAP_RELAX: .text {{.+}}.o #SHT_PROGBITS,SHF_ALLOC|SHF_EXECINSTR,2

### Relaxations are disabled.
RUN: %link %linkopts --no-relax %t.o -o %t.3.out -MapStyle txt -Map %t.3.map

RUN: %filecheck %s --input-file=%t.3.map --check-prefix=MAP_NORELAX
MAP_NORELAX: # LinkStats Begin
MAP_NORELAX: # RelaxationBytesMissed : 20
MAP_NORELAX: # RelaxationBytesMissed : 30
MAP_NORELAX: # LinkStats End

MAP_NORELAX: .text {{.+}}, Alignment: 0x2, Flags: SHF_ALLOC|SHF_EXECINSTR, Type: SHT_PROGBITS
MAP_NORELAX: # RelaxationBytesMissed : 20
MAP_NORELAX: # RelaxationBytesMissed : 30
MAP_NORELAX: .text {{.+}}.o #SHT_PROGBITS,SHF_ALLOC|SHF_EXECINSTR,2
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