compiler_rt: add __negsi2, __negdi2, __negti2

- use negXi2.zig to prevent confusion with negXf2.zig
- used for size optimized builds and machines without carry instruction
- tests: special cases 0, -INT_MIN
  * use divTrunc range and shift with constant offsets

See #1290

Author: Jan Philipp Hafer

CMakeLists.txt

@@ -498,6 +498,7 @@ set(ZIG_STAGE2_SOURCES
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/muloti4.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/multi3.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/negXf2.zig"
+    "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/negXi2.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/os_version_check.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/parity.zig"
     "${CMAKE_SOURCE_DIR}/lib/std/special/compiler_rt/popcount.zig"

lib/std/special/compiler_rt.zig

@@ -382,6 +382,12 @@ comptime {
         }
 
         // Integral arithmetic
+        const __negsi2 = @import("compiler_rt/negXi2.zig").__negsi2;
+        @export(__negsi2, .{ .name = "__negsi2", .linkage = linkage });
+        const __negdi2 = @import("compiler_rt/negXi2.zig").__negdi2;
+        @export(__negdi2, .{ .name = "__negdi2", .linkage = linkage });
+        const __negti2 = @import("compiler_rt/negXi2.zig").__negti2;
+        @export(__negti2, .{ .name = "__negti2", .linkage = linkage });
         const __mulsi3 = @import("compiler_rt/int.zig").__mulsi3;
         @export(__mulsi3, .{ .name = "__mulsi3", .linkage = linkage });
         const __muldi3 = @import("compiler_rt/muldi3.zig").__muldi3;

lib/std/special/compiler_rt/negXi2.zig

@@ -0,0 +1,33 @@
+const std = @import("std");
+const builtin = @import("builtin");
+
+// neg - negate (the number)
+// - negXi2_generic for unoptimized little and big endian
+
+// sfffffff = 2^31-1
+// two's complement inverting bits and add 1 would result in -INT_MIN == 0
+// => -INT_MIN = -2^31 forbidden
+
+// * size optimized builds
+// * machines that dont support carry operations
+
+fn negXi2_generic(comptime T: type) fn (a: T) callconv(.C) T {
+    return struct {
+        fn f(a: T) callconv(.C) T {
+            @setRuntimeSafety(builtin.is_test);
+            return -a;
+        }
+    }.f;
+}
+
+pub const __negsi2 = negXi2_generic(i32);
+
+pub const __negdi2 = negXi2_generic(i64);
+
+pub const __negti2 = negXi2_generic(i128);
+
+test {
+    _ = @import("negsi2_test.zig");
+    _ = @import("negdi2_test.zig");
+    _ = @import("negti2_test.zig");
+}