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Improve vector comparison == != for horizontal reduction

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gingerBill
2022-05-28 13:42:58 +01:00
parent 4db533ff71
commit 618d3bf62f
1 changed files with 28 additions and 9 deletions
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37
src/llvm_backend_expr.cpp
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@@ -2585,16 +2585,35 @@ lbValue lb_emit_comp(lbProcedure *p, TokenKind op_kind, lbValue left, lbValue ri
}
GB_ASSERT_MSG(mask != nullptr, "Unhandled comparison kind %s (%s) %.*s %s (%s)", type_to_string(left.type), type_to_string(base_type(left.type)), LIT(token_strings[op_kind]), type_to_string(right.type), type_to_string(base_type(right.type)));
// TODO(bill): is this a good approach to dealing with comparisons of vectors?
char const *name = "llvm.vector.reduce.umax";
LLVMTypeRef types[1] = {LLVMTypeOf(mask)};
unsigned id = LLVMLookupIntrinsicID(name, gb_strlen(name));
GB_ASSERT_MSG(id != 0, "Unable to find %s.%s", name, LLVMPrintTypeToString(types[0]));
LLVMValueRef ip = LLVMGetIntrinsicDeclaration(p->module->mod, id, types, gb_count_of(types));
/* NOTE(bill, 2022-05-28):
Thanks to Per Vognsen, sign extending <N x i1> to
a vector of the same width as the input vector, bit casting to an integer,
and then comparing against zero is the better option
See: https://lists.llvm.org/pipermail/llvm-dev/2012-September/053046.html
LLVMValueRef args[1] = {};
args[0] = mask;
res.value = LLVMBuildCall(p->builder, ip, args, gb_count_of(args), "");
// Example assuming 128-bit vector
%1 = <4 x float> ...
%2 = <4 x float> ...
%3 = fcmp oeq <4 x float> %1, %2
%4 = sext <4 x i1> %3 to <4 x i32>
%5 = bitcast <4 x i32> %4 to i128
%6 = icmp ne i128 %5, 0
br i1 %6, label %true1, label %false2
This will result in 1 cmpps + 1 ptest + 1 br
(even without SSE4.1, contrary to what the mail list states, because of pmovmskb)
*/
unsigned count = cast(unsigned)get_array_type_count(a);
unsigned elem_sz = cast(unsigned)(type_size_of(elem)*8);
LLVMTypeRef mask_type = LLVMVectorType(LLVMIntTypeInContext(p->module->ctx, elem_sz), count);
mask = LLVMBuildSExtOrBitCast(p->builder, mask, mask_type, "");
LLVMTypeRef mask_int_type = LLVMIntTypeInContext(p->module->ctx, cast(unsigned)(8*type_size_of(a)));
LLVMValueRef mask_int = LLVMBuildBitCast(p->builder, mask, mask_int_type, "");
res.value = LLVMBuildICmp(p->builder, LLVMIntNE, mask_int, LLVMConstNull(LLVMTypeOf(mask_int)), "");
return res;
} else {