[gcc r16-6907] [RISC-V][PR rtl-optimization/121787] Work around bad cfglayout interaction with asm goto

[Jeff Law]

https://gcc.gnu.org/g:63e0c271e984a7f63208f3517c110ccb6b33d8e1

commit r16-6907-g63e0c271e984a7f63208f3517c110ccb6b33d8e1
Author: Jeff Law <jeffrey.law@oss.qualcomm.com>
Date:   Mon Jan 19 15:53:22 2026 -0700

    [RISC-V][PR rtl-optimization/121787] Work around bad cfglayout interaction with asm goto
    
    This is a suggestion from Richi in the PR.
    
    The RISC-V backend calls the loop initialization routines during setup for
    vsetvl insertion/optimization.  Right now that uses LOOPS_NORMAL which allows
    various adjustments to the loop structure.  The interaction between those CFG
    adjustments and asm goto support is putting the CFG into an undesirable state.
    
    There's potentially an issue in the CFG layout bits, but we can punt that out
    by using AVOID_CFG_MODIFICATIONS when calling loop_optimizer_init.  My review
    of the vsetvl code doesn't show any direct need for clean preheaders, latches,
    etc -- the biggest thing it needs is for infinite loops to be connected to the
    exit block which is handled outside of loop_optimizer_init.
    
    So this is a workaround, but enough to get the PR off the regression list.
    
    Waiting for pre-commit CI to do its thing, though it has already passed
    riscv{32,64}-elf for me.  Bootstrap on the Pioneer is in flight.
    
            PR rtl-optimization/121787
    gcc/
            * config/riscv/riscv-vsetvl.cc (pre_vsetvl): Adjust call to
            loop_optimizer_init to avoid making CFG changes.
    
    gcc/testsuite/
            * gcc.target/riscv/pr121787-1.c: New test.
            * gcc.target/riscv/pr121787-2.c: New test.

Diff:
---
 gcc/config/riscv/riscv-vsetvl.cc            |  2 +-
 gcc/testsuite/gcc.target/riscv/pr121787-1.c | 20 ++++++++++++++++++++
 gcc/testsuite/gcc.target/riscv/pr121787-2.c | 20 ++++++++++++++++++++
 3 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/gcc/config/riscv/riscv-vsetvl.cc b/gcc/config/riscv/riscv-vsetvl.cc
index 7b7003ff5fd5..64fa809b8012 100644
--- a/gcc/config/riscv/riscv-vsetvl.cc
+++ b/gcc/config/riscv/riscv-vsetvl.cc
@@ -2422,7 +2422,7 @@ public:
   {
     /* Initialization of RTL_SSA.  */
     calculate_dominance_info (CDI_DOMINATORS);
-    loop_optimizer_init (LOOPS_NORMAL);
+    loop_optimizer_init (AVOID_CFG_MODIFICATIONS);
     /* Create FAKE edges for infinite loops.  */
     connect_infinite_loops_to_exit ();
     df_analyze ();
diff --git a/gcc/testsuite/gcc.target/riscv/pr121787-1.c b/gcc/testsuite/gcc.target/riscv/pr121787-1.c
new file mode 100644
index 000000000000..44a7f2295c7c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/pr121787-1.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64 -O" { target rv64 } } */
+/* { dg-options "-march=rv32gcv -mabi=ilp32 -O" { target rv32 } } */
+
+#include <stdint-gcc.h>
+typedef int a;
+int32_t b, e;
+int32_t **c;
+uint8_t d(int32_t *, int32_t *, uint16_t, const int32_t *, int32_t **);
+uint32_t f() {
+  uint16_t g;
+  d(0, &b, g, &b, c);
+  e = (__attribute__((__vector_size__(sizeof(a)))) a){}[4];
+}
+uint8_t d(int32_t *, int32_t *, uint16_t, const int32_t *, int32_t **) {
+  asm goto("" : : : : i);
+i:
+j:
+  asm goto("" : : : : j);
+}
diff --git a/gcc/testsuite/gcc.target/riscv/pr121787-2.c b/gcc/testsuite/gcc.target/riscv/pr121787-2.c
new file mode 100644
index 000000000000..e25366d70143
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/pr121787-2.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64 -O" { target rv64 } } */
+/* { dg-options "-march=rv32gcv -mabi=ilp32 -O" { target rv32 } } */
+
+#include <stdint-gcc.h>
+typedef int a;
+int32_t b, e;
+int32_t **c;
+uint8_t d(int32_t *, int32_t *, uint16_t, const int32_t *, int32_t **);
+uint32_t f(int a1) {
+  uint16_t g;
+  d(0, &b, g, &b, c);
+  e = (__attribute__((__vector_size__(sizeof(a)*16))) a){}[a1];
+}
+uint8_t d(int32_t *, int32_t *, uint16_t, const int32_t *, int32_t **) {
+  asm goto("#asm1" : : : : i);
+i:
+j:
+  asm goto("#asm2" : : : : j);
+}