RISC-V: Suppress cross CC sibcall optimization from vector

In general, tail call optimization requires that the callee's saved
registers are a superset of the caller's.

The Standard Vector Calling Convention Variant (assembler: .variant_cc)
requires that a function with this calling convention preserves vector
registers v1-v7 and v24-v31 across calls (i.e. callee-saved).  However,
the same set of registers are (function-local) temporary registers
(i.e. caller-saved) on the normal (non-vector) calling convention.

Even if a function with this calling convention variant calls another
function with a non-vector calling convention, those vector registers
are correctly clobbered -- except when the sibling (tail) call
optimization occurs as it violates the general rule mentioned above.

If this happens, following function body:

1.  Save v1-v7 and v24-v31 for clobbering
2.  Call another function with a non-vector calling convention
    (which may destroy v1-v7 and/or v24-v31)
3.  Restore v1-v7 and v24-v31
4.  Return.

may be incorrectly optimized into the following sequence:

1.  Save v1-v7 and v24-v31 for clobbering
2.  Restore v1-v7 and v24-v31 (?!)
3.  Jump to another function with a non-vector calling convention
    (which may destroy v1-v7 and/or v24-v31).

This commit suppresses cross CC sibling call optimization from
the vector calling convention variant.

gcc/ChangeLog:

	* config/riscv/riscv.cc (riscv_function_ok_for_sibcall):
	Suppress cross calling convention sibcall optimization from
	the vector calling convention variant.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall.c: New test.
	* gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall-indirect-1.c: Ditto.
	* gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall-indirect-2.c: Ditto.

4 files changed, 84 insertions, 0 deletions

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 17eb45a..b931036 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -11994,6 +11994,12 @@ riscv_function_ok_for_sibcall (tree decl ATTRIBUTE_UNUSED,
   if (cfun->machine->interrupt_handler_p)
     return false;
 
+  /* Don't use sibcall if a non-vector CC function is being called
+     from a vector CC function.  */
+  if ((riscv_cc) crtl->abi->id () == RISCV_CC_V
+      && (riscv_cc) expr_callee_abi (exp).id () != RISCV_CC_V)
+    return false;
+
   /* Don't use sibcalls in the large model, because a sibcall instruction
      expanding and a epilogue expanding both use RISCV_PROLOGUE_TEMP
      register.  */
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall-indirect-1.c b/gcc/testsuite/gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall-indirect-1.c
new file mode 100644
index 0000000..54ff106
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall-indirect-1.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64d -O2" } */
+
+void __attribute__((riscv_vector_cc))
+f_try_sibcall_v2v_indirect (void __attribute__((riscv_vector_cc))
+			    (*func) (void))
+{
+  func ();
+}
+
+/* { dg-final { scan-assembler-times "\\.variant_cc\tf_try_sibcall_v2v_indirect\n" 1 } } */
+/* { dg-final { scan-assembler-times "\tjr\ta0\n" 1 } } */
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall-indirect-2.c b/gcc/testsuite/gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall-indirect-2.c
new file mode 100644
index 0000000..121ac0f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall-indirect-2.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64d -O2" } */
+
+void __attribute__((riscv_vector_cc))
+f_try_sibcall_v2n_indirect (void (*func) (void))
+{
+  func ();
+}
+
+/* { dg-final { scan-assembler-times "\\.variant_cc\tf_try_sibcall_v2n_indirect\n" 1 } } */
+/* { dg-final { scan-assembler-times "\tjalr\ta0\n" 1 } } */
+/* { dg-final { scan-assembler-times "\tjr\tra\n" 1 } } */
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall.c b/gcc/testsuite/gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall.c
new file mode 100644
index 0000000..ccfc38777
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/base/abi-call-variant_cc-sibcall.c
@@ -0,0 +1,54 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv -mabi=lp64d -O2" } */
+
+void f_ext_n2n (void);
+void f_ext_v2n (void);
+void __attribute__((riscv_vector_cc)) f_ext_n2v (void);
+void __attribute__((riscv_vector_cc)) f_ext_v2v (void);
+
+/* { dg-final { scan-assembler-times "\\.variant_cc\tf_ext_n2n\n" 0 } } */
+/* { dg-final { scan-assembler-times "\\.variant_cc\tf_ext_v2n\n" 0 } } */
+/* { dg-final { scan-assembler-times "\\.variant_cc\tf_ext_n2v\n" 1 } } */
+/* { dg-final { scan-assembler-times "\\.variant_cc\tf_ext_v2v\n" 1 } } */
+
+void
+f_try_sibcall_n2n (void)
+{
+  f_ext_n2n ();
+}
+
+/* { dg-final { scan-assembler-times "\\.variant_cc\tf_try_sibcall_n2n\n" 0 } } */
+/* { dg-final { scan-assembler-times "\ttail\tf_ext_n2n\n" 1 } } */
+/* { dg-final { scan-assembler-times "\tcall\tf_ext_n2n\n" 0 } } */
+
+void
+f_try_sibcall_n2v (void)
+{
+  f_ext_n2v ();
+}
+
+/* { dg-final { scan-assembler-times "\\.variant_cc\tf_try_sibcall_n2v\n" 0 } } */
+/* { dg-final { scan-assembler-times "\ttail\tf_ext_n2v\n" 1 } } */
+/* { dg-final { scan-assembler-times "\tcall\tf_ext_n2v\n" 0 } } */
+
+void __attribute__((riscv_vector_cc))
+f_try_sibcall_v2n (void)
+{
+  /* Vector to normal: sibling call optimization shall be
+     suppressed to preserve caller's registers: v1-v7 and v24-v31.  */
+  f_ext_v2n ();
+}
+
+/* { dg-final { scan-assembler-times "\\.variant_cc\tf_try_sibcall_v2n\n" 1 } } */
+/* { dg-final { scan-assembler-times "\ttail\tf_ext_v2n\n" 0 } } */
+/* { dg-final { scan-assembler-times "\tcall\tf_ext_v2n\n" 1 } } */
+
+void __attribute__((riscv_vector_cc))
+f_try_sibcall_v2v (void)
+{
+  f_ext_v2v ();
+}
+
+/* { dg-final { scan-assembler-times "\\.variant_cc\tf_try_sibcall_v2v\n" 1 } } */
+/* { dg-final { scan-assembler-times "\ttail\tf_ext_v2v\n" 1 } } */
+/* { dg-final { scan-assembler-times "\tcall\tf_ext_v2v\n" 0 } } */