LoongArch: Remove undefined behavior from code [PR 106097]

C++2017 and previous standard description:

The value of E1 << E2 is E1 left-shifted E2 bit positions;
vacated bits are zero-filled. If E1 has an unsigned type,
the value of the result is E1×2E2, reduced modulo one more
than the maximum value representable inthe result type.
Otherwise, if E1 has a signed type and non-negative value,
and E1×2E2 is representablein the corresponding unsigned
type of the result type, then that value, converted to the
result type, is the resulting value; otherwise, the behavior
is undefined.

The value of E1 >> E2 is E1 right-shifted E2 bit positions.
If E1 has an unsigned type or if E1 has a signed type and
a non-negative value, the value of the result is the integral
part of the quotient of E1/2E2. If E1 has a signed type and
a negative value, the resulting value is implementation-defined.

gcc/ChangeLog:

	PR target/106097
	* config/loongarch/loongarch.cc (loongarch_build_integer):
	Remove undefined behavior from code.

diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index c8502b0..48d9ccd 100644 (file)
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -160,7 +160,7 @@ enum loongarch_load_imm_method
 struct loongarch_integer_op
 {
   enum rtx_code code;
-  unsigned HOST_WIDE_INT value;
+  HOST_WIDE_INT value;
   enum loongarch_load_imm_method method;
 };
 
@@ -1468,7 +1468,7 @@ loongarch_build_integer (struct loongarch_integer_op *codes,
   unsigned int cost = 0;
 
   /* Get the lower 32 bits of the value.  */
-  HOST_WIDE_INT low_part = TARGET_64BIT ? value << 32 >> 32 : value;
+  HOST_WIDE_INT low_part = (int32_t)value;
 
   if (IMM12_OPERAND (low_part) || IMM12_OPERAND_UNSIGNED (low_part))
     {
@@ -1502,6 +1502,7 @@ loongarch_build_integer (struct loongarch_integer_op *codes,
       bool lu52i[2] = {(value & LU52I_B) == 0, (value & LU52I_B) == LU52I_B};
 
       int sign31 = (value & (1UL << 31)) >> 31;
+      int sign51 = (value & (1UL << 51)) >> 51;
       /* Determine whether the upper 32 bits are sign-extended from the lower
         32 bits. If it is, the instructions to load the high order can be
         ommitted.  */
@@ -1512,12 +1513,12 @@ loongarch_build_integer (struct loongarch_integer_op *codes,
       else if (lu32i[sign31])
        {
          codes[cost].method = METHOD_LU52I;
-         codes[cost].value = (value >> 52) << 52;
+         codes[cost].value = value & LU52I_B;
          return cost + 1;
        }
 
       codes[cost].method = METHOD_LU32I;
-      codes[cost].value = ((value << 12) >> 44) << 32;
+      codes[cost].value = (value & LU32I_B) | (sign51 ? LU52I_B : 0);
       cost++;
 
       /* Determine whether the 52-61 bits are sign-extended from the low order,
@@ -1525,7 +1526,7 @@ loongarch_build_integer (struct loongarch_integer_op *codes,
       if (!lu52i[(value & (1ULL << 51)) >> 51])
        {
          codes[cost].method = METHOD_LU52I;
-         codes[cost].value = (value >> 52) << 52;
+         codes[cost].value = value & LU52I_B;
          cost++;
        }
     }