[RISCV] Enable GP relaxation for Linux#201265
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We have supported GP relaxation in https://reviews.llvm.org/D143673 for a long time, but we made it disabled by default. This PR enables it in Clang driver when targeting Linux. (Please remind me if I missed the context why we disabled it on Linux).
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@llvm/pr-subscribers-clang @llvm/pr-subscribers-clang-driver Author: Pengcheng Wang (wangpc-pp) ChangesWe have supported GP relaxation in https://reviews.llvm.org/D143673 This PR enables it in Clang driver when targeting Linux. (Please remind me if I missed the context why we disabled it on Linux). Full diff: https://github.com/llvm/llvm-project/pull/201265.diff 4 Files Affected:
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 132d9128a795b..d52076c037b76 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -812,6 +812,7 @@ RISC-V Support
- Tenstorrent Ascalon D8 was renamed to Ascalon X. Use `tt-ascalon-x` with `-mcpu` or `-mtune`.
- Intrinsics were added for the 'Zvabd` (RISC-V Integer Vector Absolute Difference) extension.
- Intrinsics were added for the 'Zvzip` (Reordering Structured Data in Vector Registers) extension.
+- GP relaxation was enabled by default on Linux.
CUDA/HIP Language Changes
^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
index 131dd725c7289..5be5045ea6252 100644
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -343,6 +343,16 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
CmdArgs.push_back("--no-relax");
}
+ // Default-enable LLD's --relax-gp for RISC-V on Linux when LLD is used and
+ // linker relaxation is not disabled by -mno-relax.
+ if (Triple.isRISCV() && Triple.isOSLinux()) {
+ bool IsLLD = false;
+ ToolChain.GetLinkerPath(&IsLLD);
+ if (IsLLD &&
+ Args.hasFlag(options::OPT_mrelax, options::OPT_mno_relax, true))
+ CmdArgs.push_back("--relax-gp");
+ }
+
const bool IsShared = Args.hasArg(options::OPT_shared);
if (IsShared)
CmdArgs.push_back("-shared");
diff --git a/clang/test/Driver/riscv32-toolchain.c b/clang/test/Driver/riscv32-toolchain.c
index 04acf1e7edbe0..272e55c19df97 100644
--- a/clang/test/Driver/riscv32-toolchain.c
+++ b/clang/test/Driver/riscv32-toolchain.c
@@ -247,6 +247,31 @@
// RUN: | FileCheck -check-prefix=CHECK-RV32-GNU-RELAX %s
// CHECK-RV32-GNU-RELAX-NOT: "--no-relax"
+/// Check that "--relax-gp" is forwarded to LLD for RISC-V on Linux by default.
+// RUN: %clang -### %s -fuse-ld=lld -B%S/Inputs/lld -no-pie \
+// RUN: --target=riscv32-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=ilp32 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV32-LLD-RELAXGP %s
+// CHECK-RV32-LLD-RELAXGP: "--relax-gp"
+
+/// Check that "--relax-gp" is NOT forwarded to GNU ld for RISC-V on Linux.
+// RUN: env "PATH=" %clang -### %s -fuse-ld=ld -no-pie \
+// RUN: --target=riscv32-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=ilp32 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV32-GNU-NO-RELAXGP %s
+// CHECK-RV32-GNU-NO-RELAXGP-NOT: "--relax-gp"
+
+/// Check that "--relax-gp" is NOT forwarded to LLD when -mno-relax is set.
+// RUN: %clang -### %s -fuse-ld=lld -B%S/Inputs/lld -no-pie -mno-relax \
+// RUN: --target=riscv32-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=ilp32 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV32-LLD-NORELAX-NOGP %s
+// CHECK-RV32-LLD-NORELAX-NOGP: "--no-relax"
+// CHECK-RV32-LLD-NORELAX-NOGP-NOT: "--relax-gp"
+
/// Check that "-static -pie" is forwarded to linker when "-static-pie" is used
// RUN: %clang -static-pie -### %s -fuse-ld= \
// RUN: --target=riscv32-unknown-elf -rtlib=platform --unwindlib=platform \
diff --git a/clang/test/Driver/riscv64-toolchain.c b/clang/test/Driver/riscv64-toolchain.c
index 378f3d9db7bad..6820b1a34806d 100644
--- a/clang/test/Driver/riscv64-toolchain.c
+++ b/clang/test/Driver/riscv64-toolchain.c
@@ -203,6 +203,31 @@
// RUN: | FileCheck -check-prefix=CHECK-RV64-GNU-RELAX %s
// CHECK-RV64-GNU-RELAX-NOT: "--no-relax"
+/// Check that "--relax-gp" is forwarded to LLD for RISC-V on Linux by default.
+// RUN: %clang -### %s -fuse-ld=lld -B%S/Inputs/lld -no-pie \
+// RUN: --target=riscv64-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=lp64 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV64-LLD-RELAXGP %s
+// CHECK-RV64-LLD-RELAXGP: "--relax-gp"
+
+/// Check that "--relax-gp" is NOT forwarded to GNU ld for RISC-V on Linux.
+// RUN: env "PATH=" %clang -### %s -fuse-ld=ld -no-pie \
+// RUN: --target=riscv64-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=lp64 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV64-GNU-NO-RELAXGP %s
+// CHECK-RV64-GNU-NO-RELAXGP-NOT: "--relax-gp"
+
+/// Check that "--relax-gp" is NOT forwarded to LLD when -mno-relax is set.
+// RUN: %clang -### %s -fuse-ld=lld -B%S/Inputs/lld -no-pie -mno-relax \
+// RUN: --target=riscv64-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=lp64 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV64-LLD-NORELAX-NOGP %s
+// CHECK-RV64-LLD-NORELAX-NOGP: "--no-relax"
+// CHECK-RV64-LLD-NORELAX-NOGP-NOT: "--relax-gp"
+
/// Check that "-static -pie" is forwarded to linker when "-static-pie" is used
// RUN: %clang -static-pie -### %s -fuse-ld= \
// RUN: --target=riscv64-unknown-elf -rtlib=platform --unwindlib=platform \
|
|
@llvm/pr-subscribers-backend-risc-v Author: Pengcheng Wang (wangpc-pp) ChangesWe have supported GP relaxation in https://reviews.llvm.org/D143673 This PR enables it in Clang driver when targeting Linux. (Please remind me if I missed the context why we disabled it on Linux). Full diff: https://github.com/llvm/llvm-project/pull/201265.diff 4 Files Affected:
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 132d9128a795b..d52076c037b76 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -812,6 +812,7 @@ RISC-V Support
- Tenstorrent Ascalon D8 was renamed to Ascalon X. Use `tt-ascalon-x` with `-mcpu` or `-mtune`.
- Intrinsics were added for the 'Zvabd` (RISC-V Integer Vector Absolute Difference) extension.
- Intrinsics were added for the 'Zvzip` (Reordering Structured Data in Vector Registers) extension.
+- GP relaxation was enabled by default on Linux.
CUDA/HIP Language Changes
^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
index 131dd725c7289..5be5045ea6252 100644
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -343,6 +343,16 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
CmdArgs.push_back("--no-relax");
}
+ // Default-enable LLD's --relax-gp for RISC-V on Linux when LLD is used and
+ // linker relaxation is not disabled by -mno-relax.
+ if (Triple.isRISCV() && Triple.isOSLinux()) {
+ bool IsLLD = false;
+ ToolChain.GetLinkerPath(&IsLLD);
+ if (IsLLD &&
+ Args.hasFlag(options::OPT_mrelax, options::OPT_mno_relax, true))
+ CmdArgs.push_back("--relax-gp");
+ }
+
const bool IsShared = Args.hasArg(options::OPT_shared);
if (IsShared)
CmdArgs.push_back("-shared");
diff --git a/clang/test/Driver/riscv32-toolchain.c b/clang/test/Driver/riscv32-toolchain.c
index 04acf1e7edbe0..272e55c19df97 100644
--- a/clang/test/Driver/riscv32-toolchain.c
+++ b/clang/test/Driver/riscv32-toolchain.c
@@ -247,6 +247,31 @@
// RUN: | FileCheck -check-prefix=CHECK-RV32-GNU-RELAX %s
// CHECK-RV32-GNU-RELAX-NOT: "--no-relax"
+/// Check that "--relax-gp" is forwarded to LLD for RISC-V on Linux by default.
+// RUN: %clang -### %s -fuse-ld=lld -B%S/Inputs/lld -no-pie \
+// RUN: --target=riscv32-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=ilp32 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV32-LLD-RELAXGP %s
+// CHECK-RV32-LLD-RELAXGP: "--relax-gp"
+
+/// Check that "--relax-gp" is NOT forwarded to GNU ld for RISC-V on Linux.
+// RUN: env "PATH=" %clang -### %s -fuse-ld=ld -no-pie \
+// RUN: --target=riscv32-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=ilp32 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV32-GNU-NO-RELAXGP %s
+// CHECK-RV32-GNU-NO-RELAXGP-NOT: "--relax-gp"
+
+/// Check that "--relax-gp" is NOT forwarded to LLD when -mno-relax is set.
+// RUN: %clang -### %s -fuse-ld=lld -B%S/Inputs/lld -no-pie -mno-relax \
+// RUN: --target=riscv32-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=ilp32 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV32-LLD-NORELAX-NOGP %s
+// CHECK-RV32-LLD-NORELAX-NOGP: "--no-relax"
+// CHECK-RV32-LLD-NORELAX-NOGP-NOT: "--relax-gp"
+
/// Check that "-static -pie" is forwarded to linker when "-static-pie" is used
// RUN: %clang -static-pie -### %s -fuse-ld= \
// RUN: --target=riscv32-unknown-elf -rtlib=platform --unwindlib=platform \
diff --git a/clang/test/Driver/riscv64-toolchain.c b/clang/test/Driver/riscv64-toolchain.c
index 378f3d9db7bad..6820b1a34806d 100644
--- a/clang/test/Driver/riscv64-toolchain.c
+++ b/clang/test/Driver/riscv64-toolchain.c
@@ -203,6 +203,31 @@
// RUN: | FileCheck -check-prefix=CHECK-RV64-GNU-RELAX %s
// CHECK-RV64-GNU-RELAX-NOT: "--no-relax"
+/// Check that "--relax-gp" is forwarded to LLD for RISC-V on Linux by default.
+// RUN: %clang -### %s -fuse-ld=lld -B%S/Inputs/lld -no-pie \
+// RUN: --target=riscv64-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=lp64 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV64-LLD-RELAXGP %s
+// CHECK-RV64-LLD-RELAXGP: "--relax-gp"
+
+/// Check that "--relax-gp" is NOT forwarded to GNU ld for RISC-V on Linux.
+// RUN: env "PATH=" %clang -### %s -fuse-ld=ld -no-pie \
+// RUN: --target=riscv64-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=lp64 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV64-GNU-NO-RELAXGP %s
+// CHECK-RV64-GNU-NO-RELAXGP-NOT: "--relax-gp"
+
+/// Check that "--relax-gp" is NOT forwarded to LLD when -mno-relax is set.
+// RUN: %clang -### %s -fuse-ld=lld -B%S/Inputs/lld -no-pie -mno-relax \
+// RUN: --target=riscv64-unknown-linux-gnu --rtlib=platform --unwindlib=platform -mabi=lp64 \
+// RUN: --gcc-toolchain=%S/Inputs/multilib_riscv_linux_sdk \
+// RUN: --sysroot=%S/Inputs/multilib_riscv_linux_sdk/sysroot 2>&1 \
+// RUN: | FileCheck -check-prefix=CHECK-RV64-LLD-NORELAX-NOGP %s
+// CHECK-RV64-LLD-NORELAX-NOGP: "--no-relax"
+// CHECK-RV64-LLD-NORELAX-NOGP-NOT: "--relax-gp"
+
/// Check that "-static -pie" is forwarded to linker when "-static-pie" is used
// RUN: %clang -static-pie -### %s -fuse-ld= \
// RUN: --target=riscv64-unknown-elf -rtlib=platform --unwindlib=platform \
|
lenary
reviewed
Jun 3, 2026
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| // Default-enable LLD's --relax-gp for RISC-V on Linux when LLD is used and | ||
| // linker relaxation is not disabled by -mno-relax. | ||
| if (Triple.isRISCV() && Triple.isOSLinux()) { | ||
| bool IsLLD = false; | ||
| ToolChain.GetLinkerPath(&IsLLD); | ||
| if (IsLLD && | ||
| Args.hasFlag(options::OPT_mrelax, options::OPT_mno_relax, true)) | ||
| CmdArgs.push_back("--relax-gp"); | ||
| } |
Member
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Do we know in the driver if the intention is to create a shared library? If so, we should not pass --relax-gp, I don't think.
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I don't know if we can just check if -static/-shared exists.
Member
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Passing the gp relax flag and sending it to -shared shouldn't cause any problems, since the linker mainly checks whether the __global_pointer$ symbol is defined and whether relocation is supported.
So I would incline just pass without checking it's -shared/-static/-fPIE/&$%^$^, that may just complicate the condition here.
Contributor
|
The GP relaxation in lld only works for medlow without PIC. Linux defaults to PIE usually doesn't it? |
Contributor
Author
Get it. Does the gcc in OS distros also default to PIE? |
Member
That depend on distro, but most distro are default to PIE. Single command to check: |
Contributor
Author
|
Should I proceed with this? TBH, GP relaxation doesn't make too many differences to code size and performance. I am just trying to fill the gap between Clang/LLD and GCC/Binutils. |
Member
I prefer no. Note that |
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We have supported GP relaxation in https://reviews.llvm.org/D143673
for a long time, but we made it disabled by default.
This PR enables it in Clang driver when targeting Linux.
(Please remind me if I missed the context why we disabled it on Linux).