Merge pull request #24416 from JuliaLang/yyc/codegen/alloc

Improve allocation optimization with gc_preserve intrinsics

src/llvm-alloc-opt.cpp

@@ -606,13 +606,24 @@ void AllocOpt::replaceUsesWith(Instruction *orig_inst, Instruction *new_inst,
                 call->eraseFromParent();
                 return;
             }
+            // Also remove the preserve intrinsics so that it can be better optimized.
+            if (gc_preserve_begin && gc_preserve_begin == call->getCalledFunction()) {
+                while (!call->use_empty()) {
+                    auto end = cast<Instruction>(*call->user_begin());
+                    // gc_preserve_end returns void.
+                    assert(end->use_empty());
+                    end->eraseFromParent();
+                }
+                call->eraseFromParent();
+                return;
+            }
             if (auto intrinsic = dyn_cast<IntrinsicInst>(call)) {
                 if (Intrinsic::ID ID = intrinsic->getIntrinsicID()) {
                     replaceIntrinsicUseWith(intrinsic, ID, orig_i, new_i);
                     return;
                 }
             }
-            // remove from operand bundle or arguments for gc_perserve_begin
+            // remove from operand bundle
             Type *orig_t = orig_i->getType();
             user->replaceUsesOfWith(orig_i, ConstantPointerNull::get(cast<PointerType>(orig_t)));
         }

test/llvmpasses/alloc-opt2.jl

@@ -0,0 +1,57 @@
+# RUN: julia --startup-file=no %s | opt -load libjulia.so -AllocOpt -S - | FileCheck %s
+
+isz = sizeof(UInt) == 8 ? "i64" : "i32"
+
+println("""
+%jl_value_t = type opaque
+@tag = external addrspace(10) global %jl_value_t
+""")
+
+# Test that the gc_preserve intrinsics are deleted directly.
+
+# CHECK-LABEL: @preserve_branches
+# CHECK: alloca i64
+# CHECK: call %jl_value_t*** @julia.ptls_states()
+# CHECK: L1:
+# CHECK-NEXT: call void @llvm.lifetime.start{{.*}}(i64 8,
+# CHECK-NEXT: @external_function()
+# CHECK-NEXT: br i1 %b2, label %L2, label %L3
+
+# CHECK: L2:
+# CHECK-NOT: call void @llvm.lifetime.end{{.*}}(i64 8,
+# CHECK: @external_function()
+# CHECK-NEXT: br label %L3
+
+# CHECK: L3:
+# CHECK-NEXT: call void @llvm.lifetime.end{{.*}}(i64 8,
+println("""
+define void @preserve_branches(i8* %fptr, i1 %b, i1 %b2) {
+  %ptls = call %jl_value_t*** @julia.ptls_states()
+  %ptls_i8 = bitcast %jl_value_t*** %ptls to i8*
+  br i1 %b, label %L1, label %L3
+
+L1:
+  %v = call noalias %jl_value_t addrspace(10)* @julia.gc_alloc_obj(i8* %ptls_i8, $isz 8, %jl_value_t addrspace(10)* @tag)
+  %tok = call token (...) @llvm.julia.gc_preserve_begin(%jl_value_t addrspace(10)* %v)
+  call void @external_function()
+  br i1 %b2, label %L2, label %L3
+
+L2:
+  call void @external_function()
+  br label %L3
+
+L3:
+  ret void
+}
+""")
+# CHECK-LABEL: }
+
+println("""
+declare void @external_function()
+declare %jl_value_t*** @julia.ptls_states()
+declare noalias %jl_value_t addrspace(10)* @julia.gc_alloc_obj(i8*, $isz, %jl_value_t addrspace(10)*)
+declare i64 @julia.pointer_from_objref(%jl_value_t addrspace(11)*)
+declare void @llvm.memcpy.p11i8.p0i8.i64(i8 addrspace(11)* nocapture writeonly, i8* nocapture readonly, i64, i32, i1)
+declare token @llvm.julia.gc_preserve_begin(...)
+declare void @llvm.julia.gc_preserve_end(token)
+""")