[PowerPC][altivec] Correct modulo number of vec_promote on vector char

According to https://www.ibm.com/docs/en/xl-c-and-cpp-linux/16.1.1?topic=functions-vec-promote, the index should be input modulo the number of elements in the vector. When the type is `vector char`, the number of elements should be 16.

Reviewed By: qiucf

Differential Revision: https://reviews.llvm.org/D158484

clang/lib/Headers/altivec.h

@@ -14648,14 +14648,14 @@ static __inline__ void __ATTRS_o_ai vec_stvrxl(vector float __a, int __b,
 static __inline__ vector signed char __ATTRS_o_ai vec_promote(signed char __a,
                                                               int __b) {
   vector signed char __res = (vector signed char)(0);
-  __res[__b & 0x7] = __a;
+  __res[__b & 0xf] = __a;
   return __res;
 }
 
 static __inline__ vector unsigned char __ATTRS_o_ai
 vec_promote(unsigned char __a, int __b) {
   vector unsigned char __res = (vector unsigned char)(0);
-  __res[__b & 0x7] = __a;
+  __res[__b & 0xf] = __a;
   return __res;
 }
 

clang/test/CodeGen/PowerPC/builtins-ppc-vsx.c

@@ -2250,18 +2250,18 @@ res_vull = vec_promote(ull, 0);
 
 res_vsc = vec_promote(asc[0], 8);
 // CHECK: store <16 x i8> zeroinitializer
-// CHECK: [[IDX:%.*]] = and i32 {{.*}}, 7
+// CHECK: [[IDX:%.*]] = and i32 {{.*}}, 15
 // CHECK: insertelement <16 x i8> {{.*}}, i8 {{.*}}, i32 [[IDX]]
 // CHECK-LE: store <16 x i8> zeroinitializer
-// CHECK-LE: [[IDX:%.*]] = and i32 {{.*}}, 7
+// CHECK-LE: [[IDX:%.*]] = and i32 {{.*}}, 15
 // CHECK-LE: insertelement <16 x i8> {{.*}}, i8 {{.*}}, i32 [[IDX]]
 
 res_vuc = vec_promote(auc[0], 8);
 // CHECK: store <16 x i8> zeroinitializer
-// CHECK: [[IDX:%.*]] = and i32 {{.*}}, 7
+// CHECK: [[IDX:%.*]] = and i32 {{.*}}, 15
 // CHECK: insertelement <16 x i8> {{.*}}, i8 {{.*}}, i32 [[IDX]]
 // CHECK-LE: store <16 x i8> zeroinitializer
-// CHECK-LE: [[IDX:%.*]] = and i32 {{.*}}, 7
+// CHECK-LE: [[IDX:%.*]] = and i32 {{.*}}, 15
 // CHECK-LE: insertelement <16 x i8> {{.*}}, i8 {{.*}}, i32 [[IDX]]
 }