[PowerPC][altivec] Optimize codegen of vec_promote

According to https://www.ibm.com/docs/en/xl-c-and-cpp-linux/16.1.1?topic=functions-vec-promote, elements not specified by the input index argument are undefined. So that we don't need to set these elements to be zeros.

Reviewed By: nemanjai, #powerpc

Differential Revision: https://reviews.llvm.org/D158487

clang/lib/Headers/altivec.h

@@ -14647,67 +14647,86 @@ 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);
+  const vector signed char __zero = (vector signed char)0;
+  vector signed char __res =
+      __builtin_shufflevector(__zero, __zero, -1, -1, -1, -1, -1, -1, -1, -1,
+                              -1, -1, -1, -1, -1, -1, -1, -1);
   __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);
+  const vector unsigned char __zero = (vector unsigned char)(0);
+  vector unsigned char __res =
+      __builtin_shufflevector(__zero, __zero, -1, -1, -1, -1, -1, -1, -1, -1,
+                              -1, -1, -1, -1, -1, -1, -1, -1);
   __res[__b & 0xf] = __a;
   return __res;
 }
 
 static __inline__ vector short __ATTRS_o_ai vec_promote(short __a, int __b) {
-  vector short __res = (vector short)(0);
+  const vector short __zero = (vector short)(0);
+  vector short __res =
+      __builtin_shufflevector(__zero, __zero, -1, -1, -1, -1, -1, -1, -1, -1);
   __res[__b & 0x7] = __a;
   return __res;
 }
 
 static __inline__ vector unsigned short __ATTRS_o_ai
 vec_promote(unsigned short __a, int __b) {
-  vector unsigned short __res = (vector unsigned short)(0);
+  const vector unsigned short __zero = (vector unsigned short)(0);
+  vector unsigned short __res =
+      __builtin_shufflevector(__zero, __zero, -1, -1, -1, -1, -1, -1, -1, -1);
   __res[__b & 0x7] = __a;
   return __res;
 }
 
 static __inline__ vector int __ATTRS_o_ai vec_promote(int __a, int __b) {
-  vector int __res = (vector int)(0);
+  const vector int __zero = (vector int)(0);
+  vector int __res = __builtin_shufflevector(__zero, __zero, -1, -1, -1, -1);
   __res[__b & 0x3] = __a;
   return __res;
 }
 
 static __inline__ vector unsigned int __ATTRS_o_ai vec_promote(unsigned int __a,
                                                                int __b) {
-  vector unsigned int __res = (vector unsigned int)(0);
+  const vector unsigned int __zero = (vector unsigned int)(0);
+  vector unsigned int __res =
+      __builtin_shufflevector(__zero, __zero, -1, -1, -1, -1);
   __res[__b & 0x3] = __a;
   return __res;
 }
 
 static __inline__ vector float __ATTRS_o_ai vec_promote(float __a, int __b) {
-  vector float __res = (vector float)(0);
+  const vector float __zero = (vector float)(0);
+  vector float __res = __builtin_shufflevector(__zero, __zero, -1, -1, -1, -1);
   __res[__b & 0x3] = __a;
   return __res;
 }
 
 #ifdef __VSX__
 static __inline__ vector double __ATTRS_o_ai vec_promote(double __a, int __b) {
-  vector double __res = (vector double)(0);
+  const vector double __zero = (vector double)(0);
+  vector double __res = __builtin_shufflevector(__zero, __zero, -1, -1);
   __res[__b & 0x1] = __a;
   return __res;
 }
 
 static __inline__ vector signed long long __ATTRS_o_ai
 vec_promote(signed long long __a, int __b) {
-  vector signed long long __res = (vector signed long long)(0);
+  const vector signed long long __zero = (vector signed long long)(0);
+  vector signed long long __res =
+      __builtin_shufflevector(__zero, __zero, -1, -1);
   __res[__b & 0x1] = __a;
   return __res;
 }
 
 static __inline__ vector unsigned long long __ATTRS_o_ai
 vec_promote(unsigned long long __a, int __b) {
-  vector unsigned long long __res = (vector unsigned long long)(0);
+  const vector unsigned long long __zero = (vector unsigned long long)(0);
+  vector unsigned long long __res =
+      __builtin_shufflevector(__zero, __zero, -1, -1);
   __res[__b & 0x1] = __a;
   return __res;
 }

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

@@ -2232,35 +2232,45 @@ res_vuc = vec_xxsldwi(vuc, vuc, 1);
 
 res_vd = vec_promote(d, 0);
 // CHECK: store <2 x double> zeroinitializer
+// CHECK: store <2 x double> poison
 // CHECK: insertelement <2 x double>
 // CHECK-LE: store <2 x double> zeroinitializer
+// CHECK-LE: store <2 x double> poison
 // CHECK-LE: insertelement <2 x double>
 
 res_vsll = vec_promote(sll, 0);
 // CHECK: store <2 x i64> zeroinitializer
+// CHECK: store <2 x i64> poison
 // CHECK: insertelement <2 x i64>
 // CHECK-LE: store <2 x i64> zeroinitializer
+// CHECK-LE: store <2 x i64> poison
 // CHECK-LE: insertelement <2 x i64>
 
 res_vull = vec_promote(ull, 0);
 // CHECK: store <2 x i64> zeroinitializer
+// CHECK: store <2 x i64> poison
 // CHECK: insertelement <2 x i64>
 // CHECK-LE: store <2 x i64> zeroinitializer
+// CHECK-LE: store <2 x i64> poison
 // CHECK-LE: insertelement <2 x i64>
 
 res_vsc = vec_promote(asc[0], 8);
 // CHECK: store <16 x i8> zeroinitializer
+// CHECK: store <16 x i8> poison
 // CHECK: [[IDX:%.*]] = and i32 {{.*}}, 15
 // CHECK: insertelement <16 x i8> {{.*}}, i8 {{.*}}, i32 [[IDX]]
 // CHECK-LE: store <16 x i8> zeroinitializer
+// CHECK-LE: store <16 x i8> poison
 // 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: store <16 x i8> poison
 // CHECK: [[IDX:%.*]] = and i32 {{.*}}, 15
 // CHECK: insertelement <16 x i8> {{.*}}, i8 {{.*}}, i32 [[IDX]]
 // CHECK-LE: store <16 x i8> zeroinitializer
+// CHECK-LE: store <16 x i8> poison
 // CHECK-LE: [[IDX:%.*]] = and i32 {{.*}}, 15
 // CHECK-LE: insertelement <16 x i8> {{.*}}, i8 {{.*}}, i32 [[IDX]]
 }