gentle ping :)
Luke Zhuang
------------------------------------------------------------------
From:Luke Zhuang <[email protected]>
Send Time:Thu, Jun 25, 2026, 13:45
To:"gcc-patches"<[email protected]>
CC:"kito.cheng"<[email protected]>; palmer<[email protected]>;
"rdapp.gcc"<[email protected]>; andrew<[email protected]>;
"jim.wilson.gcc"<[email protected]>;
"juzhe.zhong"<[email protected]>; rdsandiford<[email protected]>;
"jeffrey.law"<[email protected]>;
"zhuangzhi.zz"<[email protected]>; Luke
Zhuang<[email protected]>
Subject:[PATCH v4] RISC-V: Declare TLSDESC clobbers for vector registers and
CSRs per psABI
From: "Luke Zhuang" <[email protected]>
Per the RISC-V psABI, the TLSDESC resolver clobbers a0 and t0 in the
base case. With the new psABI update
(https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/496
<https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/496 >),
when the V extension is enabled, it additionally clobbers all vector
registers and vector CSRs.
This patch updates the clobbering of tlsdesc define_insn: clobbering
not only a0 and t0, but also all V-regs (using 4 x LMUL8 reg
groups covering all 32 physical V-regs), and 4 vector CSRs
(vl/vtype/vxrm/vxstat).
Three new tests are added covering GPR, vector register, and vector
CSR clobber behavior.
gcc/ChangeLog:
* config/riscv/riscv.md (VXSAT_REGNUM): New constant.
(@tlsdesc<mode>): update clobbering.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/tlsdesc_clobber.c: New test.
* gcc.target/riscv/tlsdesc_clobber_v.c: New test.
* gcc.target/riscv/tlsdesc_clobber_v_csr.c: New test.
---
gcc/config/riscv/riscv.md | 11 +++-
.../gcc.target/riscv/tlsdesc_clobber.c | 29 ++++++++++
.../gcc.target/riscv/tlsdesc_clobber_v.c | 56 +++++++++++++++++++
.../gcc.target/riscv/tlsdesc_clobber_v_csr.c | 39 +++++++++++++
4 files changed, 134 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.target/riscv/tlsdesc_clobber.c
create mode 100644 gcc/testsuite/gcc.target/riscv/tlsdesc_clobber_v.c
create mode 100644 gcc/testsuite/gcc.target/riscv/tlsdesc_clobber_v_csr.c
diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
index b90bfe0745a..d3cddacb566 100644
--- a/gcc/config/riscv/riscv.md
+++ b/gcc/config/riscv/riscv.md
@@ -181,6 +181,7 @@
(VTYPE_REGNUM 67)
(VXRM_REGNUM 68)
(FRM_REGNUM 69)
+ (VXSAT_REGNUM 70)
])
(include "predicates.md")
@@ -2478,7 +2479,15 @@
(unspec:P
[(match_operand:P 0 "symbolic_operand" "")]
UNSPEC_TLSDESC))
- (clobber (reg:P T0_REGNUM))]
+ (clobber (reg:P T0_REGNUM))
+ (clobber (reg:RVVM8QI 96))
+ (clobber (reg:RVVM8QI 104))
+ (clobber (reg:RVVM8QI 112))
+ (clobber (reg:RVVM8QI 120))
+ (clobber (reg:SI VL_REGNUM))
+ (clobber (reg:SI VTYPE_REGNUM))
+ (clobber (reg:SI VXRM_REGNUM))
+ (clobber (reg:SI VXSAT_REGNUM))]
"TARGET_TLSDESC"
{
return ".LT%=: auipc\ta0,%%tlsdesc_hi(%0)\;"
diff --git a/gcc/testsuite/gcc.target/riscv/tlsdesc_clobber.c
b/gcc/testsuite/gcc.target/riscv/tlsdesc_clobber.c
new file mode 100644
index 00000000000..6a004d6820f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/tlsdesc_clobber.c
@@ -0,0 +1,29 @@
+/* Verify that the TLSDESC resolver only clobbers a0 and t0 while assuming
+ all other registers as preserved per its custom ABI (no vector case),
+ which is different from a normal call. */
+
+/* { dg-do compile } */
+/* { dg-require-effective-target tls_native } */
+/* { dg-options "-O2 -fpic -mtls-dialect=desc -march=rv64gc -mabi=lp64d" } */
+/* { dg-require-effective-target fpic } */
+
+extern __thread int tls_var;
+
+long
+test_clobber (long a, long b, long c, long d)
+{
+ /* a=a0, b=a1, c=a2, d=a3.
+ TLSDESC clobbers a0 and t0 only, so the compiler must save/restore
+ a0 (by stack or mv or whatever), but should not do the same thing
+ for a1-a3 like a normal call. */
+ tls_var = 1;
+ return a + b + c + d;
+}
+
+/* The TLSDESC call should be present. */
+/* { dg-final { scan-assembler-times {jalr\tt0,} 1 } } */
+
+/* ra/a1-a3 should NOT be moved to s-regs or saved to stack. */
+/* { dg-final { scan-assembler-not {mv\ts[0-9]+,a[0-9]+} } } */
+/* { dg-final { scan-assembler-not {sd\ta[0-9]+,.*\(sp\)} } } */
+/* { dg-final { scan-assembler-not {sd\tra,.*\(sp\)} } } */
diff --git a/gcc/testsuite/gcc.target/riscv/tlsdesc_clobber_v.c
b/gcc/testsuite/gcc.target/riscv/tlsdesc_clobber_v.c
new file mode 100644
index 00000000000..a5fb350f76e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/tlsdesc_clobber_v.c
@@ -0,0 +1,56 @@
+/* Verify that when the V extension is enabled, the TLSDESC resolver clobbers
+ all vector registers per the psABI. The compiler must save/restore any
+ live vector registers across the TLSDESC call. */
+
+/* { dg-do compile } */
+/* { dg-require-effective-target tls_native } */
+/* { dg-options "-O2 -fpic -mtls-dialect=desc -march=rv64gcv -mabi=lp64d" } */
+/* { dg-require-effective-target fpic } */
+
+extern __thread int tls_var;
+
+void
+test_vector_reg_clobber (void)
+{
+ __rvv_int32m1_t v1, v2, v3, v4, v5, v6, v7, v8, v9, v10, v11, v12;
+
+ /* Write two v-regs. */
+ asm volatile ("# def v1" : "=vr"(v1));
+ asm volatile ("# def v2" : "=vr"(v2));
+ asm volatile ("# def v3" : "=vr"(v3));
+ asm volatile ("# def v4" : "=vr"(v4));
+ asm volatile ("# def v5" : "=vr"(v5));
+ asm volatile ("# def v6" : "=vr"(v6));
+ asm volatile ("# def v7" : "=vr"(v7));
+ asm volatile ("# def v8" : "=vr"(v8));
+ asm volatile ("# def v9" : "=vr"(v9));
+ asm volatile ("# def v10" : "=vr"(v10));
+ asm volatile ("# def v11" : "=vr"(v11));
+ asm volatile ("# def v12" : "=vr"(v12));
+
+ /* TLSDESC call — clobbers all vector regs. */
+ asm volatile ("" ::: "memory"); /* Prevent scheduling... */
+ tls_var = 1;
+ asm volatile ("" ::: "memory"); /* Prevent scheduling... */
+
+ /* Read the two v-regs; their live-range spans across the TLSDESC call,
+ so the compiler must emit vector store/load pairs to preserve them. */
+ asm volatile ("# use v1" : : "vr"(v1));
+ asm volatile ("# use v2" : : "vr"(v2));
+ asm volatile ("# use v3" : : "vr"(v3));
+ asm volatile ("# use v4" : : "vr"(v4));
+ asm volatile ("# use v5" : : "vr"(v5));
+ asm volatile ("# use v6" : : "vr"(v6));
+ asm volatile ("# use v7" : : "vr"(v7));
+ asm volatile ("# use v8" : : "vr"(v8));
+ asm volatile ("# use v9" : : "vr"(v9));
+ asm volatile ("# use v10" : : "vr"(v10));
+ asm volatile ("# use v11" : : "vr"(v11));
+ asm volatile ("# use v12" : : "vr"(v12));
+}
+
+/* { dg-final { scan-assembler-times {jalr\tt0,} 1 } } */
+
+/* Vector stores before and loads after the TLSDESC call. */
+/* { dg-final { scan-assembler-times {\tvs[0-9]+r\.v\t} 12 } } */
+/* { dg-final { scan-assembler-times {\tvl[0-9]+re[0-9]+\.v\t} 12 } } */
diff --git a/gcc/testsuite/gcc.target/riscv/tlsdesc_clobber_v_csr.c
b/gcc/testsuite/gcc.target/riscv/tlsdesc_clobber_v_csr.c
new file mode 100644
index 00000000000..ffb9c9a61a4
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/tlsdesc_clobber_v_csr.c
@@ -0,0 +1,39 @@
+/* Verify that when the V extension is enabled, the TLSDESC resolver clobbers
+ vector CSRs (vl, vtype, vxrm, vxsat) per the psABI. The compiler must
+ re-emit a vsetvli after the TLSDESC call to recover the vector status. */
+
+/* { dg-do compile } */
+/* { dg-require-effective-target tls_native } */
+/* { dg-options "-O2 -fpic -mtls-dialect=desc -march=rv64gcv -mabi=lp64d" } */
+/* { dg-require-effective-target fpic } */
+
+typedef int v4si __attribute__ ((vector_size (16)));
+
+extern __thread int tls_var;
+
+void
+test_vector_csr_clobber (v4si *in, v4si *out)
+{
+ v4si vec;
+
+ /* A pair of local load/store whose live-range does not span accross
+ the TLSDESC. It has a special size format so it needs a vsetvli. */
+ vec = *in;
+ *out = vec;
+
+ /* TLSDESC call — clobbers all vector CSRs including vl/vtype. */
+ asm volatile ("" ::: "memory"); /* Prevent scheduling... */
+ tls_var = 1;
+ asm volatile ("" ::: "memory"); /* Prevent scheduling... */
+
+ /* Another pair of local load/store. But since TLSDESC clobbers vl/vtype, we
+ must re-emit a vsetvli here. */
+ vec = *in;
+ *out = vec;
+}
+
+/* { dg-final { scan-assembler-times {jalr\tt0,} 1 } } */
+
+/* Two vsetvli: one before each vector segment. The second is needed because
+ TLSDESC clobbers vl/vtype. */
+/* { dg-final { scan-assembler-times {vsetvli|vsetivli} 2 } } */
--
2.47.1
