expmed: TRUNCATE value1 if needed in store_bit_field_using_insv

PR target/113179.

In `store_bit_field_using_insv`, we just use SUBREG if value_mode
>= op_mode, while in some ports, a sign_extend will be needed,
such as MIPS64:
  If either GPR rs or GPR rt does not contain sign-extended 32-bit
  values (bits 63..31 equal), then the result of the operation is
  UNPREDICTABLE.

The problem happens for the code like:
  struct xx {
        int a:4;
        int b:24;
        int c:3;
        int d:1;
  };

  void xx (struct xx *a, long long b) {
        a->d = b;
  }

In the above code, the hard register contains `b`, may be note well
sign-extended.

gcc/
	PR target/113179
	* expmed.cc(store_bit_field_using_insv): TRUNCATE value1 if
	needed.

gcc/testsuite
	PR target/113179
	* gcc.target/mips/pr113179.c: New tests.

2 files changed, 27 insertions, 3 deletions

diff --git a/gcc/expmed.cc b/gcc/expmed.cc
index 4ec035e..20f3a36 100644
--- a/gcc/expmed.cc
+++ b/gcc/expmed.cc
@@ -704,9 +704,15 @@ store_bit_field_using_insv (const extraction_insn *insv, rtx op0,
 	    }
 	  else
 	    {
-	      tmp = gen_lowpart_if_possible (op_mode, value1);
-	      if (! tmp)
-		tmp = gen_lowpart (op_mode, force_reg (value_mode, value1));
+	      if (targetm.mode_rep_extended (op_mode, value_mode) != UNKNOWN)
+		tmp = simplify_gen_unary (TRUNCATE, op_mode,
+					  value1, value_mode);
+	      else
+		{
+		  tmp = gen_lowpart_if_possible (op_mode, value1);
+		  if (! tmp)
+		    tmp = gen_lowpart (op_mode, force_reg (value_mode, value1));
+		}
 	    }
 	  value1 = tmp;
 	}
diff --git a/gcc/testsuite/gcc.target/mips/pr113179.c b/gcc/testsuite/gcc.target/mips/pr113179.c
new file mode 100644
index 0000000..f32c5a1
--- /dev/null
+++ b/gcc/testsuite/gcc.target/mips/pr113179.c
@@ -0,0 +1,18 @@
+/* Check if the operand of INS is sign-extended on MIPS64.  */
+/* { dg-options "-mips64r2 -mabi=64" } */
+/* { dg-skip-if "code quality test" { *-*-* } { "-O0" } { "" } } */
+
+struct xx {
+        int a:1;
+        int b:24;
+        int c:6;
+        int d:1;
+};
+
+long long xx (struct xx *a, long long b) {
+        a->d = b;
+        return b+1;
+}
+
+/* { dg-final { scan-assembler "\tsll\t\\\$3,\\\$5,0" } } */
+/* { dg-final { scan-assembler "\tdaddiu\t\\\$2,\\\$5,1" } } */