RISC-V: Optimize switch with sign-extended index.

	gcc/
	* expr.c (do_tablejump): When converting index to Pmode, if we have a
	sign extended promoted subreg, and the range does not have the sign bit
	set, then do a sign extend.

	* config/riscv/riscv.c (riscv_extend_comparands): In unsigned QImode
	test, check for sign extended subreg and/or constant operands, and
	do a sign extend in that case.

	gcc/testsuite/
	* gcc.target/riscv/switch-qi.c: New.
	* gcc.target/riscv/switch-si.c: New.

From-SVN: r260340

gcc/ChangeLog

+2018-05-17  Jim Wilson  <jimw@sifive.com>
+
+	* expr.c (do_tablejump): When converting index to Pmode, if we have a
+	sign extended promoted subreg, and the range does not have the sign bit
+	set, then do a sign extend.
+
+	* config/riscv/riscv.c (riscv_extend_comparands): In unsigned QImode
+	test, check for sign extended subreg and/or constant operands, and
+	do a sign extend in that case.
+
 2018-05-17  Steve Ellcey  <sellcey@cavium.com>
 
 	* config/aarch64/thunderx2t99.md (thunderx2t99_ls_both): Delete.

gcc/config/riscv/riscv.c

@@ -2002,8 +2002,18 @@ riscv_extend_comparands (rtx_code code, rtx *op0, rtx *op1)
   /* Comparisons consider all XLEN bits, so extend sub-XLEN values.  */
   if (GET_MODE_SIZE (word_mode) > GET_MODE_SIZE (GET_MODE (*op0)))
     {
-      /* It is more profitable to zero-extend QImode values.  */
-      if (unsigned_condition (code) == code && GET_MODE (*op0) == QImode)
+      /* It is more profitable to zero-extend QImode values.  But not if the
+	 first operand has already been sign-extended, and the second one is
+	 is a constant or has already been sign-extended also.  */
+      if (unsigned_condition (code) == code
+	  && (GET_MODE (*op0) == QImode
+	      && ! (GET_CODE (*op0) == SUBREG
+		    && SUBREG_PROMOTED_VAR_P (*op0)
+		    && SUBREG_PROMOTED_SIGNED_P (*op0)
+		    && (CONST_INT_P (*op1)
+			|| (GET_CODE (*op1) == SUBREG
+			    && SUBREG_PROMOTED_VAR_P (*op1)
+			    && SUBREG_PROMOTED_SIGNED_P (*op1))))))
 	{
 	  *op0 = gen_rtx_ZERO_EXTEND (word_mode, *op0);
 	  if (CONST_INT_P (*op1))

gcc/expr.c

@@ -11782,11 +11782,26 @@ do_tablejump (rtx index, machine_mode mode, rtx range, rtx table_label,
     emit_cmp_and_jump_insns (index, range, GTU, NULL_RTX, mode, 1,
 			     default_label, default_probability);
 
-
   /* If index is in range, it must fit in Pmode.
      Convert to Pmode so we can index with it.  */
   if (mode != Pmode)
-    index = convert_to_mode (Pmode, index, 1);
+    {
+      unsigned int width;
+
+      /* We know the value of INDEX is between 0 and RANGE.  If we have a
+	 sign-extended subreg, and RANGE does not have the sign bit set, then
+	 we have a value that is valid for both sign and zero extension.  In
+	 this case, we get better code if we sign extend.  */
+      if (GET_CODE (index) == SUBREG
+	  && SUBREG_PROMOTED_VAR_P (index)
+	  && SUBREG_PROMOTED_SIGNED_P (index)
+	  && ((width = GET_MODE_PRECISION (as_a <scalar_int_mode> (mode)))
+	      <= HOST_BITS_PER_WIDE_INT)
+	  && ! (UINTVAL (range) & (HOST_WIDE_INT_1U << (width - 1))))
+	index = convert_to_mode (Pmode, index, 0);
+      else
+	index = convert_to_mode (Pmode, index, 1);
+    }
 
   /* Don't let a MEM slip through, because then INDEX that comes
      out of PIC_CASE_VECTOR_ADDRESS won't be a valid address,

gcc/testsuite/ChangeLog

+2018-05-17  Jim Wilson  <jimw@sifive.com>
+
+	* gcc.target/riscv/switch-qi.c: New.
+	* gcc.target/riscv/switch-si.c: New.
+
 2018-05-17  Pat Haugen  <pthaugen@us.ibm.com>
 
 	PR target/85698

gcc/testsuite/gcc.target/riscv/switch-qi.c

+/* { dg-do compile { target { riscv64*-*-* } } } */
+/* { dg-options "-march=rv64gc -mabi=lp64 -O2" } */
+
+/* Test for riscv_extend_comparands patch.  */
+extern void asdf(int);
+void foo(signed char x) {
+  switch (x) {
+  case 0: asdf(10); break;
+  case 1: asdf(11); break;
+  case 2: asdf(12); break;
+  case 3: asdf(13); break;
+  case 4: asdf(14); break;
+  }
+}
+/* { dg-final { scan-assembler-not "andi" } } */

gcc/testsuite/gcc.target/riscv/switch-si.c

+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+/* Test for do_tablejump patch.  */
+extern void asdf(int);
+void foo(int x) {
+  switch (x) {
+  case 0: asdf(10); break;
+  case 1: asdf(11); break;
+  case 2: asdf(12); break;
+  case 3: asdf(13); break;
+  case 4: asdf(14); break;
+  }
+}
+/* { dg-final { scan-assembler-not "srli" } } */