Revert "Make emitted egal code more loopy (JuliaLang#54121)" (JuliaLang#57453)

This reverts a portion of commit
50833c8.

This algorithm is not able to handle simple cases where there is any
internal padding, such as the example of:
```
struct LotsBytes
    a::Int8
    b::NTuple{256,Int}
    c::Int
end
```

Unfortunately fixing it is a bit of a large project right now, so
reverting now to fix correctness while working on that.

Fixes JuliaLang#55513 (indirectly, by removing broken code) Maybe reopens JuliaLang#54109,
although the latency issue it proposes to fix doesn't occur on master
even with this revert (just the mediocre looking IR result output
returns)

Author: vtjnash

Compiler/test/codegen.jl

@@ -889,57 +889,6 @@ ex54166 = Union{Missing, Int64}[missing -2; missing -2];
 dims54166 = (1,2)
 @test (minimum(ex54166; dims=dims54166)[1] === missing)
 
-# #54109 - Excessive LLVM time for egal
-struct DefaultOr54109{T}
-    x::T
-    default::Bool
-end
-
-@eval struct Torture1_54109
-    $((Expr(:(::), Symbol("x$i"), DefaultOr54109{Float64}) for i = 1:897)...)
-end
-Torture1_54109() = Torture1_54109((DefaultOr54109(1.0, false) for i = 1:897)...)
-
-@eval struct Torture2_54109
-    $((Expr(:(::), Symbol("x$i"), DefaultOr54109{Float64}) for i = 1:400)...)
-    $((Expr(:(::), Symbol("x$(i+400)"), DefaultOr54109{Int16}) for i = 1:400)...)
-end
-Torture2_54109() = Torture2_54109((DefaultOr54109(1.0, false) for i = 1:400)..., (DefaultOr54109(Int16(1), false) for i = 1:400)...)
-
-@noinline egal_any54109(x, @nospecialize(y::Any)) = x === Base.compilerbarrier(:type, y)
-
-let ir1 = get_llvm(egal_any54109, Tuple{Torture1_54109, Any}),
-    ir2 = get_llvm(egal_any54109, Tuple{Torture2_54109, Any})
-
-    # We can't really do timing on CI, so instead, let's look at the length of
-    # the optimized IR. The original version had tens of thousands of lines and
-    # was slower, so just check here that we only have < 500 lines. If somebody,
-    # implements a better comparison that's larger than that, just re-benchmark
-    # this and adjust the threshold.
-
-    @test count(==('\n'), ir1) < 500
-    @test count(==('\n'), ir2) < 500
-end
-
-## Regression test for egal of a struct of this size without padding, but with
-## non-bitsegal, to make sure that it doesn't accidentally go down the accelerated
-## path.
-@eval struct BigStructAnyInt
-    $((Expr(:(::), Symbol("x$i"), Pair{Any, Int}) for i = 1:33)...)
-end
-BigStructAnyInt() = BigStructAnyInt((Union{Base.inferencebarrier(Float64), Int}=>i for i = 1:33)...)
-@test egal_any54109(BigStructAnyInt(), BigStructAnyInt())
-
-## For completeness, also test correctness, since we don't have a lot of
-## large-struct tests.
-
-# The two allocations of the same struct will likely have different padding,
-# we want to make sure we find them egal anyway - a naive memcmp would
-# accidentally look at it.
-@test egal_any54109(Torture1_54109(), Torture1_54109())
-@test egal_any54109(Torture2_54109(), Torture2_54109())
-@test !egal_any54109(Torture1_54109(), Torture1_54109((DefaultOr54109(2.0, false) for i = 1:897)...))
-
 bar54599() = Base.inferencebarrier(true) ? (Base.PkgId(Main),1) : nothing
 
 function foo54599()

src/codegen.cpp

@@ -3616,61 +3616,6 @@ static Value *emit_bitsunion_compare(jl_codectx_t &ctx, const jl_cgval_t &arg1,
     return phi;
 }
 
-struct egal_desc {
-    size_t offset;
-    size_t nrepeats;
-    size_t data_bytes;
-    size_t padding_bytes;
-};
-
-template <typename callback>
-static size_t emit_masked_bits_compare(callback &emit_desc, jl_datatype_t *aty, egal_desc &current_desc)
-{
-    // Memcmp, but with masked padding
-    size_t data_bytes = 0;
-    size_t padding_bytes = 0;
-    size_t nfields = jl_datatype_nfields(aty);
-    size_t total_size = jl_datatype_size(aty);
-    assert(aty->layout->flags.isbitsegal);
-    for (size_t i = 0; i < nfields; ++i) {
-        size_t offset = jl_field_offset(aty, i);
-        size_t fend = i == nfields - 1 ? total_size : jl_field_offset(aty, i + 1);
-        size_t fsz = jl_field_size(aty, i);
-        jl_datatype_t *fty = (jl_datatype_t*)jl_field_type(aty, i);
-        assert(jl_is_datatype(fty)); // union fields should never reach here
-        assert(fty->layout->flags.isbitsegal);
-        if (jl_field_isptr(aty, i) || !fty->layout->flags.haspadding) {
-            // The field has no internal padding
-            data_bytes += fsz;
-            if (offset + fsz == fend) {
-                // The field has no padding after. Merge this into the current
-                // comparison range and go to next field.
-            } else {
-                padding_bytes = fend - offset - fsz;
-                // Found padding. Either merge this into the current comparison
-                // range, or emit the old one and start a new one.
-                if (current_desc.data_bytes == data_bytes &&
-                        current_desc.padding_bytes == padding_bytes) {
-                    // Same as the previous range, just note that down, so we
-                    // emit this as a loop.
-                    current_desc.nrepeats += 1;
-                } else {
-                    if (current_desc.nrepeats != 0)
-                        emit_desc(current_desc);
-                    current_desc.nrepeats = 1;
-                    current_desc.data_bytes = data_bytes;
-                    current_desc.padding_bytes = padding_bytes;
-                }
-                data_bytes = 0;
-            }
-        } else {
-            // The field may have internal padding. Recurse this.
-            data_bytes += emit_masked_bits_compare(emit_desc, fty, current_desc);
-        }
-    }
-    return data_bytes;
-}
-
 static Value *emit_bits_compare(jl_codectx_t &ctx, jl_cgval_t arg1, jl_cgval_t arg2)
 {
     ++EmittedBitsCompares;
@@ -3747,92 +3692,6 @@ static Value *emit_bits_compare(jl_codectx_t &ctx, jl_cgval_t arg1, jl_cgval_t a
             }
             return ctx.builder.CreateICmpEQ(answer, ConstantInt::get(getInt32Ty(ctx.builder.getContext()), 0));
         }
-        else if (sz > 512 && jl_struct_try_layout(sty) && sty->layout->flags.isbitsegal) {
-            Value *varg1 = arg1.inline_roots.empty() && arg1.ispointer() ? data_pointer(ctx, arg1) :
-                value_to_pointer(ctx, arg1).V;
-            Value *varg2 = arg2.inline_roots.empty() && arg2.ispointer() ? data_pointer(ctx, arg2) :
-                value_to_pointer(ctx, arg2).V;
-            varg1 = emit_pointer_from_objref(ctx, varg1);
-            varg2 = emit_pointer_from_objref(ctx, varg2);
-
-            // See above for why we want to do this
-            SmallVector<Value*, 0> gc_uses;
-            gc_uses.append(get_gc_roots_for(ctx, arg1));
-            gc_uses.append(get_gc_roots_for(ctx, arg2));
-            OperandBundleDef OpBundle("jl_roots", gc_uses);
-
-            Value *answer = nullptr;
-            auto emit_desc = [&](egal_desc desc) {
-                Value *ptr1 = varg1;
-                Value *ptr2 = varg2;
-                if (desc.offset != 0) {
-                    ptr1 = emit_ptrgep(ctx, ptr1, desc.offset);
-                    ptr2 = emit_ptrgep(ctx, ptr2, desc.offset);
-                }
-
-                Value *new_ptr1 = ptr1;
-                Value *endptr1 = nullptr;
-                BasicBlock *postBB = nullptr;
-                BasicBlock *loopBB = nullptr;
-                PHINode *answerphi = nullptr;
-                if (desc.nrepeats != 1) {
-                    // Set up loop
-                    endptr1 = emit_ptrgep(ctx, ptr1, desc.nrepeats * (desc.data_bytes + desc.padding_bytes));;
-
-                    BasicBlock *currBB = ctx.builder.GetInsertBlock();
-                    loopBB = BasicBlock::Create(ctx.builder.getContext(), "egal_loop", ctx.f);
-                    postBB = BasicBlock::Create(ctx.builder.getContext(), "post", ctx.f);
-                    ctx.builder.CreateBr(loopBB);
-
-                    ctx.builder.SetInsertPoint(loopBB);
-                    Type *TInt1 = getInt1Ty(ctx.builder.getContext());
-                    answerphi = ctx.builder.CreatePHI(TInt1, 2);
-                    answerphi->addIncoming(answer ? answer : ConstantInt::get(TInt1, 1), currBB);
-                    answer = answerphi;
-
-                    PHINode *itr1 = ctx.builder.CreatePHI(ptr1->getType(), 2);
-                    PHINode *itr2 = ctx.builder.CreatePHI(ptr2->getType(), 2);
-
-                    new_ptr1 = emit_ptrgep(ctx, itr1, desc.data_bytes + desc.padding_bytes);
-                    itr1->addIncoming(ptr1, currBB);
-                    itr1->addIncoming(new_ptr1, loopBB);
-
-                    Value *new_ptr2 = emit_ptrgep(ctx, itr2, desc.data_bytes + desc.padding_bytes);
-                    itr2->addIncoming(ptr2, currBB);
-                    itr2->addIncoming(new_ptr2, loopBB);
-
-                    ptr1 = itr1;
-                    ptr2 = itr2;
-                }
-
-                // Emit memcmp. TODO: LLVM has a pass to expand this for additional
-                // performance.
-                Value *this_answer = ctx.builder.CreateCall(prepare_call(memcmp_func),
-                    { ptr1,
-                      ptr2,
-                      ConstantInt::get(ctx.types().T_size, desc.data_bytes) },
-                    ArrayRef<OperandBundleDef>(&OpBundle, gc_uses.empty() ? 0 : 1));
-                this_answer = ctx.builder.CreateICmpEQ(this_answer, ConstantInt::get(getInt32Ty(ctx.builder.getContext()), 0));
-                answer = answer ? ctx.builder.CreateAnd(answer, this_answer) : this_answer;
-                if (endptr1) {
-                    answerphi->addIncoming(answer, loopBB);
-                    Value *loopend = ctx.builder.CreateICmpEQ(new_ptr1, endptr1);
-                    ctx.builder.CreateCondBr(loopend, postBB, loopBB);
-                    ctx.builder.SetInsertPoint(postBB);
-                }
-            };
-            egal_desc current_desc = {0};
-            size_t trailing_data_bytes = emit_masked_bits_compare(emit_desc, sty, current_desc);
-            assert(current_desc.nrepeats != 0);
-            emit_desc(current_desc);
-            if (trailing_data_bytes != 0) {
-                current_desc.nrepeats = 1;
-                current_desc.data_bytes = trailing_data_bytes;
-                current_desc.padding_bytes = 0;
-                emit_desc(current_desc);
-            }
-            return answer;
-        }
         else {
             jl_svec_t *types = sty->types;
             Value *answer = ConstantInt::get(getInt1Ty(ctx.builder.getContext()), 1);