Make `simd_shuffle` act closer to `swizzle`

1 files changed, 11 insertions, 3 deletions

diff --git a/src/llvm_backend_proc.cpp b/src/llvm_backend_proc.cpp
index 7a86427d4..2bffa111c 100644
--- a/src/llvm_backend_proc.cpp
+++ b/src/llvm_backend_proc.cpp
@@ -1282,15 +1282,23 @@ lbValue lb_build_builtin_simd_proc(lbProcedure *p, Ast *expr, TypeAndValue const
 	case BuiltinProc_simd_shuffle:
 		{
 			arg1 = lb_build_expr(p, ce->args[1]);
-			arg2 = lb_build_expr(p, ce->args[2]);
 
 			Type *vt = arg0.type;
 			GB_ASSERT(vt->kind == Type_SimdVector);
 
-			LLVMValueRef mask = arg2.value;
 
+			i64 mask_count = ce->args.count-2;
 			i64 max_count = vt->SimdVector.count*2;
-			LLVMValueRef max_mask = llvm_splat_int(max_count, lb_type(m, arg2.type->SimdVector.elem), max_count-1);
+
+			LLVMValueRef *values = gb_alloc_array(temporary_allocator(), LLVMValueRef, mask_count);
+			for (isize i = 0; i < max_count; i++) {
+				lbValue idx = lb_build_expr(p, ce->args[i+2]);
+				GB_ASSERT(LLVMIsConstant(idx.value));
+				values[i] = idx.value;
+			}
+			LLVMValueRef mask = LLVMConstVector(values, cast(unsigned)mask_count);
+
+			LLVMValueRef max_mask = llvm_splat_int(mask_count, lb_type(m, t_u32), max_count-1);
 			mask = LLVMBuildAnd(p->builder, mask, max_mask, "");
 
 			res.value = LLVMBuildShuffleVector(p->builder, arg0.value, arg1.value, mask, "");