LoongArch: Warn about right shifts of negative numbers

The GNU Assembler User Guide says that the right shift operator ">>"
in an expression is the same as the C operator.

On LoongArch the assembler directives and instructions do not treat
negative numbers ">>" the same way. The directives treats negative
numbers ">>" as logical right shifts while the instructions treats them
as arithmetic right shifts.

The right shift of negative numbers in the instructions may be changed
from an arithmetic right shift to a logical right shift in the future,
and a warning is issued for this.

diff --git a/gas/config/loongarch-parse.y b/gas/config/loongarch-parse.y
index ac35deee1de86823a6085a093edb2fc143fbcc3b..97055fe42c3dd2961da130ef1c52017b703cfeca 100644 (file)
--- a/gas/config/loongarch-parse.y
+++ b/gas/config/loongarch-parse.y
@@ -225,6 +225,9 @@ emit_bin (int op)
          opr1 = opr1 << opr2;
          break;
        case RIGHT_OP:
+         if (opr1 < 0)
+           as_warn(_("Right shift of negative numbers may be changed "
+                 "from arithmetic right shift to logical right shift!"));
          /* Algorithm right shift.  */
          opr1 = (offsetT)opr1 >> (offsetT)opr2;
          break;

diff --git a/gas/testsuite/gas/loongarch/loongarch.exp b/gas/testsuite/gas/loongarch/loongarch.exp
index 87595b91cceda8734153f995fbd18c61f5911440..0e836f7f217c1f0b389953458ec496f5ef1d70bc 100644 (file)
--- a/gas/testsuite/gas/loongarch/loongarch.exp
+++ b/gas/testsuite/gas/loongarch/loongarch.exp
@@ -36,5 +36,6 @@ if [istarget loongarch*-*-*] {
   if [istarget loongarch64-*-*] {
     run_list_test "illegal-operand"
     run_list_test "pseudo_op_option_fail"
+    run_list_test "negative_right_shift"
   }
 }

diff --git a/gas/testsuite/gas/loongarch/negative_right_shift.d b/gas/testsuite/gas/loongarch/negative_right_shift.d
new file mode 100644 (file)
index 0000000..4237710
--- /dev/null
+++ b/gas/testsuite/gas/loongarch/negative_right_shift.d
@@ -0,0 +1,40 @@
+#as:
+#objdump: -d
+#skip: loongarch32-*-*
+#warning_output: negative_right_shift.l
+
+.*:     file format .*
+
+
+Disassembly of section \.text:
+
+0+ <directives>:
+   0:  03400000        nop
+   4:  00000001        \.word          0x00000001
+   8:  00000001        \.word          0x00000001
+
+0+c <insns>:
+   c:  02bff9ac        addi.w          \$t0, \$t1, -2
+  10:  02fff9ac        addi.d          \$t0, \$t1, -2
+  14:  13fff9ac        addu16i.d       \$t0, \$t1, -2
+  18:  15ffffcc        lu12i.w         \$t0, -2
+  1c:  17ffffcc        lu32i.d         \$t0, -2
+  20:  033ff9ac        lu52i.d         \$t0, \$t1, -2
+  24:  023ff9ac        slti            \$t0, \$t1, -2
+  28:  027ff9ac        sltui           \$t0, \$t1, -2
+  2c:  19ffffcc        pcaddi          \$t0, -2
+  30:  1dffffcc        pcaddu12i       \$t0, -2
+  34:  1fffffcc        pcaddu18i       \$t0, -2
+  38:  1bffffcc        pcalau12i       \$t0, -2
+  3c:  02bffdac        addi.w          \$t0, \$t1, -1
+  40:  02fffdac        addi.d          \$t0, \$t1, -1
+  44:  13fffdac        addu16i.d       \$t0, \$t1, -1
+  48:  15ffffec        lu12i.w         \$t0, -1
+  4c:  17ffffec        lu32i.d         \$t0, -1
+  50:  033ffdac        lu52i.d         \$t0, \$t1, -1
+  54:  023ffdac        slti            \$t0, \$t1, -1
+  58:  027ffdac        sltui           \$t0, \$t1, -1
+  5c:  19ffffec        pcaddi          \$t0, -1
+  60:  1dffffec        pcaddu12i       \$t0, -1
+  64:  1fffffec        pcaddu18i       \$t0, -1
+  68:  1bffffec        pcalau12i       \$t0, -1

diff --git a/gas/testsuite/gas/loongarch/negative_right_shift.l b/gas/testsuite/gas/loongarch/negative_right_shift.l
new file mode 100644 (file)
index 0000000..6edb2a5
--- /dev/null
+++ b/gas/testsuite/gas/loongarch/negative_right_shift.l
@@ -0,0 +1,13 @@
+.*: Assembler messages:
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!
+.*: Warning: Right shift of negative numbers may be changed from arithmetic right shift to logical right shift!

diff --git a/gas/testsuite/gas/loongarch/negative_right_shift.s b/gas/testsuite/gas/loongarch/negative_right_shift.s
new file mode 100644 (file)
index 0000000..c6a8a1e
--- /dev/null
+++ b/gas/testsuite/gas/loongarch/negative_right_shift.s
@@ -0,0 +1,32 @@
+directives:
+.align   -1>>62
+.word    -1>>63
+.4byte   -1>>63
+
+insns:
+addi.w   $t0, $t1, -1<<1
+addi.d   $t0, $t1, -1<<1
+addu16i.d $t0, $t1, -1<<1
+lu12i.w          $t0, -1<<1
+lu32i.d          $t0, -1<<1
+lu52i.d          $t0, $t1, -1<<1
+slti     $t0, $t1, -1<<1
+sltui    $t0, $t1, -1<<1
+pcaddi   $t0, -1<<1
+pcaddu12i $t0, -1<<1
+pcaddu18i $t0, -1<<1
+pcalau12i $t0, -1<<1
+
+# warn
+addi.w   $t0, $t1, -1>>63
+addi.d   $t0, $t1, -1>>63
+addu16i.d $t0, $t1, -1>>63
+lu12i.w          $t0, -1>>63
+lu32i.d          $t0, -1>>63
+lu52i.d          $t0, $t1, -1>>63
+slti     $t0, $t1, -1>>63
+sltui    $t0, $t1, -1>>63
+pcaddi   $t0, -1>>63
+pcaddu12i $t0, -1>>63
+pcaddu18i $t0, -1>>63
+pcalau12i $t0, -1>>63