[PATCH 4/4] RISC-V: Fix ICE by expansion and register coercion

[Tsukasa OI <research_trasio@irq.a4lg.com>]

From: Tsukasa OI <research_trasio@irq.a4lg.com>

A "prefetch" instruction on RISC-V GCC emits a machine hint instruction
directly when the 'Zicbop' extension is enabled but it could cause an ICE
when the address argument of __builtin_prefetch is an integral constant
(such like 0 [NULL] or some other [but possibly not all] fixed addresses).

This is caused by the fact that the "r" constraint is not actually checked
and something other than a register can be the first argument of the
"prefetch" RTL instruction.

It fixes the problem by changing "prefetch" from a native instruction to
an expansion and coercing the address to a register there.

gcc/ChangeLog:

	* config/riscv/riscv.md (prefetch): Expand to a native prefetch
	instruction instead of emitting a machine instruction directly.
	Coerce the address argument into a register.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/cmo-zicbop-by-common-ice-1.c: New ICE test.
	* gcc.target/riscv/cmo-zicbop-by-common-ice-2.c: Ditto.
---
 gcc/config/riscv/riscv.md                     | 43 ++++++++++++-------
 .../riscv/cmo-zicbop-by-common-ice-1.c        | 13 ++++++
 .../riscv/cmo-zicbop-by-common-ice-2.c        |  7 +++
 3 files changed, 48 insertions(+), 15 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/riscv/cmo-zicbop-by-common-ice-1.c
 create mode 100644 gcc/testsuite/gcc.target/riscv/cmo-zicbop-by-common-ice-2.c

diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
index e67a6d1f1b81..bf232345b1ab 100644
--- a/gcc/config/riscv/riscv.md
+++ b/gcc/config/riscv/riscv.md
@@ -3479,21 +3479,6 @@
   [(set_attr "type" "cbo")]
 )
 
-(define_insn "prefetch"
-  [(prefetch (match_operand 0 "address_operand" "r")
-             (match_operand 1 "imm5_operand" "i")
-             (match_operand 2 "const_int_operand" "n"))]
-  "TARGET_ZICBOP"
-{
-  switch (INTVAL (operands[1]))
-  {
-    case 0: return "prefetch.r\t%a0";
-    case 1: return "prefetch.w\t%a0";
-    default: gcc_unreachable ();
-  }
-}
-  [(set_attr "type" "cbo")])
-
 (define_insn "riscv_prefetch_r_<mode>"
   [(unspec_volatile:X [(match_operand:X 0 "register_operand" "r")]
 		       UNSPECV_PREFETCH_R)]
@@ -3508,6 +3493,34 @@
   "prefetch.w\t0(%0)"
   [(set_attr "type" "cbo")])
 
+(define_expand "prefetch"
+  [(prefetch (match_operand 0 "address_operand" "")
+	     (match_operand 1 "const_int_operand" "")
+	     (match_operand 2 "const_int_operand" ""))]
+  "TARGET_ZICBOP"
+{
+  operands[0] = force_reg (Pmode, operands[0]);
+  switch (INTVAL (operands[1]))
+    {
+    case 0:
+      if (TARGET_64BIT)
+	emit_insn (gen_riscv_prefetch_r_di (operands[0]));
+      else
+	emit_insn (gen_riscv_prefetch_r_si (operands[0]));
+      break;
+    case 1:
+      if (TARGET_64BIT)
+	emit_insn (gen_riscv_prefetch_w_di (operands[0]));
+      else
+	emit_insn (gen_riscv_prefetch_w_si (operands[0]));
+      break;
+    default:
+      gcc_unreachable ();
+    }
+  DONE;
+}
+  [(set_attr "type" "cbo")])
+
 (define_expand "extv<mode>"
   [(set (match_operand:GPR 0 "register_operand" "=r")
 	(sign_extract:GPR (match_operand:GPR 1 "register_operand" "r")
diff --git a/gcc/testsuite/gcc.target/riscv/cmo-zicbop-by-common-ice-1.c b/gcc/testsuite/gcc.target/riscv/cmo-zicbop-by-common-ice-1.c
new file mode 100644
index 000000000000..47e83f29cc5c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/cmo-zicbop-by-common-ice-1.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv32i_zicbop -mabi=ilp32" } */
+
+void foo (void)
+{
+  /* Second argument defaults to zero (read).  */
+  __builtin_prefetch (0);
+  __builtin_prefetch (0, 0);
+  __builtin_prefetch (0, 1);
+}
+
+/* { dg-final { scan-assembler-times "prefetch\\.r" 2 } } */
+/* { dg-final { scan-assembler-times "prefetch\\.w" 1 } } */
diff --git a/gcc/testsuite/gcc.target/riscv/cmo-zicbop-by-common-ice-2.c b/gcc/testsuite/gcc.target/riscv/cmo-zicbop-by-common-ice-2.c
new file mode 100644
index 000000000000..a245b8163c1f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/cmo-zicbop-by-common-ice-2.c
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64i_zicbop -mabi=lp64" } */
+
+#include "cmo-zicbop-by-common-ice-1.c"
+
+/* { dg-final { scan-assembler-times "prefetch\\.r" 2 } } */
+/* { dg-final { scan-assembler-times "prefetch\\.w" 1 } } */
-- 
2.42.0