[PowerPC] Handle __builtin_xxpermdi the same way as GCC does

[nemanjai]

Summary

The codegen for this builtin was initially implemented to match GCC. However, due to interest from users GCC changed behaviour to account for the big endian bias of the instruction and correct it. This patch brings the handling inline with GCC.

[lu-zero]

Looks good, thank you!

[efriedma]

lib/CodeGen/CGBuiltin.cpp

10833–10834

Please fix the comment.

[nemanjai]

lib/CodeGen/CGBuiltin.cpp

10833–10834

Ah yes. Good catch. Thanks Eli. I'll fix up the comment on the commit.

[sfertile]

lib/CodeGen/CGBuiltin.cpp

10834–10838

There is an extra ;on each line.

lib/CodeGen/CGBuiltin.cpp

Value *CodeGenFunction::EmitPPCBuiltinExpr(unsigned BuiltinID,
 
   case PPC::BI__builtin_vsx_xxpermdi: {
     ConstantInt *ArgCI = dyn_cast<ConstantInt>(Ops[2]);
     assert(ArgCI && "Third arg must be constant integer!");
 
     unsigned Index = ArgCI->getZExtValue();
     Ops[0] = Builder.CreateBitCast(Ops[0], llvm::VectorType::get(Int64Ty, 2));
     Ops[1] = Builder.CreateBitCast(Ops[1], llvm::VectorType::get(Int64Ty, 2));
 
-    // Element zero comes from the first input vector and element one comes from
-    // the second. The element indices within each vector are numbered in big
-    // endian order so the shuffle mask must be adjusted for this on little
-    // endian platforms (i.e. index is complemented and source vector reversed).
-    unsigned ElemIdx0;
-    unsigned ElemIdx1;
-    if (getTarget().isLittleEndian()) {
-      ElemIdx0 = (~Index & 1) + 2;
-      ElemIdx1 = (~Index & 2) >> 1;
-    } else { // BigEndian
-      ElemIdx0 = (Index & 2) >> 1;
-      ElemIdx1 = 2 + (Index & 1);
-    }
+    // Account for endianness by treating this as just a shuffle. So we use the
+    // same indices for both LE and BE in order to produce expected results in
+    // both cases.
+    unsigned ElemIdx0 = (Index & 2) >> 1;;
+    unsigned ElemIdx1 = 2 + (Index & 1);;
 
     Constant *ShuffleElts[2] = {ConstantInt::get(Int32Ty, ElemIdx0),
                                 ConstantInt::get(Int32Ty, ElemIdx1)};
     Constant *ShuffleMask = llvm::ConstantVector::get(ShuffleElts);
 
     Value *ShuffleCall =
         Builder.CreateShuffleVector(Ops[0], Ops[1], ShuffleMask);
     QualType BIRetType = E->getType();

test/CodeGen/builtins-ppc-vsx.c

 // CHECK-LE: fsub <4 x float> <float -0.000000e+00, float -0.000000e+00, float -0.000000e+00, float -0.000000e+00>, {{%[0-9]+}}
 
   res_vd = vec_neg(vd);
 // CHECK: fsub <2 x double> <double -0.000000e+00, double -0.000000e+00>, {{%[0-9]+}}
 // CHECK-LE: fsub <2 x double> <double -0.000000e+00, double -0.000000e+00>, {{%[0-9]+}}
 
 res_vd = vec_xxpermdi(vd, vd, 0);
 // CHECK: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 2>
-// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 3, i32 1>
+// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 2>
 
 res_vf = vec_xxpermdi(vf, vf, 1);
 // CHECK: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 3>
-// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 2, i32 1>
+// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 3>
 
 res_vsll = vec_xxpermdi(vsll, vsll, 2);
 // CHECK: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 1, i32 2>
-// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 3, i32 0>
+// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 1, i32 2>
 
 res_vull = vec_xxpermdi(vull, vull, 3);
 // CHECK: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 1, i32 3>
-// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 2, i32 0>
+// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 1, i32 3>
 
 res_vsi = vec_xxpermdi(vsi, vsi, 0);
 // CHECK: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 2>
-// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 3, i32 1>
+// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 2>
 
 res_vui = vec_xxpermdi(vui, vui, 1);
 // CHECK: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 3>
-// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 2, i32 1>
+// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 3>
 
 res_vss = vec_xxpermdi(vss, vss, 2);
 // CHECK: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 1, i32 2>
-// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 3, i32 0>
+// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 1, i32 2>
 
 res_vus = vec_xxpermdi(vus, vus, 3);
 // CHECK: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 1, i32 3>
-// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 2, i32 0>
+// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 1, i32 3>
 
 res_vsc = vec_xxpermdi(vsc, vsc, 0);
 // CHECK: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 2>
-// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 3, i32 1>
+// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 2>
 
 res_vuc = vec_xxpermdi(vuc, vuc, 1);
 // CHECK: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 3>
-// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 2, i32 1>
+// CHECK-LE: shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 3>
 
 res_vd = vec_xxsldwi(vd, vd, 0);
 // CHECK: shufflevector <4 x i32> %{{[0-9]+}}, <4 x i32> %{{[0-9]+}}, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 // CHECK-LE: shufflevector <4 x i32> %{{[0-9]+}}, <4 x i32> %{{[0-9]+}}, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 
 res_vf = vec_xxsldwi(vf, vf, 1);
 // CHECK: shufflevector <4 x i32> %{{[0-9]+}}, <4 x i32> %{{[0-9]+}}, <4 x i32> <i32 1, i32 2, i32 3, i32 4>
 // CHECK-LE: shufflevector <4 x i32> %{{[0-9]+}}, <4 x i32> %{{[0-9]+}}, <4 x i32> <i32 7, i32 0, i32 1, i32 2>

 // CHECK-LABEL: xxpermdi_should_not_assert
 // CHECK:  bitcast <4 x i32> %{{[0-9]+}} to <2 x i64>
 // CHECK-NEXT:  bitcast <4 x i32> %{{[0-9]+}} to <2 x i64>
 // CHECK-NEXT:  shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 2>
 // CHECK-NEXT:  bitcast <2 x i64> %{{[0-9]+}} to <4 x i32>
 
 // CHECK-LE:  bitcast <4 x i32> %{{[0-9]+}} to <2 x i64>
 // CHECK-LE-NEXT:  bitcast <4 x i32> %{{[0-9]+}} to <2 x i64>
-// CHECK-LE-NEXT:  shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 3, i32 1>
+// CHECK-LE-NEXT:  shufflevector <2 x i64> %{{[0-9]+}}, <2 x i64> %{{[0-9]+}}, <2 x i32> <i32 0, i32 2>
 // CHECK-LE-NEXT:  bitcast <2 x i64> %{{[0-9]+}} to <4 x i32>
 }
 
 vector double xxsldwi_should_not_assert(vector double a, vector double b) {
   return vec_xxsldwi(a, b, 0);
 // CHECK-LABEL: xxsldwi_should_not_assert
 // CHECK:  bitcast <2 x double> %{{[0-9]+}} to <4 x i32>
 // CHECK-NEXT:  bitcast <2 x double> %{{[0-9]+}} to <4 x i32>
 // CHECK-NEXT:  shufflevector <4 x i32> %{{[0-9]+}}, <4 x i32> %{{[0-9]+}}, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 // CHECK-NEXT:  bitcast <4 x i32> %{{[0-9]+}} to <2 x double>
 
 // CHECK-LE:  bitcast <2 x double> %{{[0-9]+}} to <4 x i32>
 // CHECK-NEXT-LE:  bitcast <2 x double> %{{[0-9]+}} to <4 x i32>
 // CHECK-NEXT-LE:  shufflevector <4 x i32> %{{[0-9]+}}, <4 x i32> %{{[0-9]+}}, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 // CHECK-NEXT-LE:  bitcast <4 x i32> %{{[0-9]+}} to <2 x double>
 }