[gcc r16-3524] RISC-V: Handle overlap in expand_vec_perm PR121742.

[Robin Dapp via Gcc-cvs]

https://gcc.gnu.org/g:f957d352bd6f240829226405e9be7960071d1b9c

commit r16-3524-gf957d352bd6f240829226405e9be7960071d1b9c
Author: Robin Dapp <rd...@ventanamicro.com>
Date:   Mon Sep 1 11:41:34 2025 +0200

    RISC-V: Handle overlap in expand_vec_perm PR121742.
    
    In a two-source gather we unconditionally overwrite target with the
    first gather's result already.  If op1 == target this clobbers the
    source operand for the second gather.  This patch uses a temporary in
    that case.
    
            PR target/121742
    
    gcc/ChangeLog:
    
            * config/riscv/riscv-v.cc (expand_vec_perm): Use temporary if
            op1 and target overlap.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.target/riscv/rvv/autovec/pr121742.c: New test.

Diff:
---
 gcc/config/riscv/riscv-v.cc                        | 11 +++++---
 .../gcc.target/riscv/rvv/autovec/pr121742.c        | 30 ++++++++++++++++++++++
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/gcc/config/riscv/riscv-v.cc b/gcc/config/riscv/riscv-v.cc
index edfb4ff4ba60..9cbd4803cda2 100644
--- a/gcc/config/riscv/riscv-v.cc
+++ b/gcc/config/riscv/riscv-v.cc
@@ -3313,15 +3313,17 @@ expand_vec_perm (rtx target, rtx op0, rtx op1, rtx sel)
   mask_mode = get_mask_mode (data_mode);
   rtx mask = gen_reg_rtx (mask_mode);
   rtx max_sel = gen_const_vector_dup (sel_mode, nunits);
+  bool overlap = reg_overlap_mentioned_p (target, op1);
+  rtx tmp_target = overlap ? gen_reg_rtx (data_mode) : target;
 
   /* Step 1: generate a mask that should select everything >= nunits into the
    * mask.  */
   expand_vec_cmp (mask, GEU, sel_mod, max_sel);
 
-  /* Step2: gather every op0 values indexed by sel into target,
+  /* Step2: gather every op0 values indexed by sel into TMP_TARGET,
            we don't need to care about the result of the element
            whose index >= nunits.  */
-  emit_vlmax_gather_insn (target, op0, sel_mod);
+  emit_vlmax_gather_insn (tmp_target, op0, sel_mod);
 
   /* Step3: shift the range from (nunits, max_of_mode] to
            [0, max_of_mode - nunits].  */
@@ -3331,7 +3333,10 @@ expand_vec_perm (rtx target, rtx op0, rtx op1, rtx sel)
 
   /* Step4: gather those into the previously masked-out elements
            of target.  */
-  emit_vlmax_masked_gather_mu_insn (target, op1, tmp, mask);
+  emit_vlmax_masked_gather_mu_insn (tmp_target, op1, tmp, mask);
+
+  if (overlap)
+    emit_move_insn (tmp_target, target);
 }
 
 /* Implement TARGET_VECTORIZE_VEC_PERM_CONST for RVV.  */
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr121742.c 
b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr121742.c
new file mode 100644
index 000000000000..08491f8108a1
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/pr121742.c
@@ -0,0 +1,30 @@
+/* { dg-do run } */
+/* { dg-require-effective-target riscv_v_ok } */
+/* { dg-options "-march=rv64gcv -mabi=lp64d -O2" } */
+
+typedef unsigned long uint64_t;
+typedef unsigned int uint32_t;
+typedef unsigned char uint8_t;
+typedef uint8_t a __attribute__((vector_size(4)));
+int b, c;
+
+uint64_t d() {
+  a e = {5, 9, 1, 5};
+  a bla = {0, 0, 0, 0};
+  int *f = &b;
+  uint32_t g = 0;
+  int i = 0;
+  for (; i < 2; i++)
+    for (c = 0; c <= 2; c++) {
+      *f ^= e[3] + 9;
+      e = __builtin_shufflevector(
+          ~__builtin_shufflevector(bla, e, 1, 4, 3, 4), e, 0, 1, 1, 7);
+    }
+  return g;
+}
+
+int main() {
+  int j = d ();
+  if (b != 0)
+    __builtin_abort ();
+}