90ba33099c
This patch canonicalizes getelementptr instructions with constant indices to use the `i8` source element type. This makes it easier for optimizations to recognize that two GEPs are identical, because they don't need to see past many different ways to express the same offset. This is a first step towards https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699. This is limited to constant GEPs only for now, as they have a clear canonical form, while we're not yet sure how exactly to deal with variable indices. The test llvm/test/Transforms/PhaseOrdering/switch_with_geps.ll gives two representative examples of the kind of optimization improvement we expect from this change. In the first test SimplifyCFG can now realize that all switch branches are actually the same. In the second test it can convert it into simple arithmetic. These are representative of common optimization failures we see in Rust. Fixes https://github.com/llvm/llvm-project/issues/69841.
74 lines
2.5 KiB
C++
74 lines
2.5 KiB
C++
// dynamic_cast
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// Ensure that dynamic casting works normally
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// RUN: %clang_cc1 %s -triple=aarch64-unknown-fuchsia -O3 -S -o - -emit-llvm | FileCheck %s
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// CHECK: define{{.*}} ptr @_Z6upcastP1B(ptr noundef readnone returned %b) local_unnamed_addr
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// CHECK-NEXT: entry:
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// CHECK-NEXT: ret ptr %b
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// CHECK-NEXT: }
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// CHECK: define{{.*}} ptr @_Z8downcastP1A(ptr noundef readonly %a) local_unnamed_addr
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// CHECK-NEXT: entry:
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// CHECK-NEXT: [[isnull:%[0-9]+]] = icmp eq ptr %a, null
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// CHECK-NEXT: br i1 [[isnull]], label %[[dynamic_cast_end:[a-z0-9._]+]], label %[[dynamic_cast_notnull:[a-z0-9._]+]]
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// CHECK: [[dynamic_cast_notnull]]:
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// CHECK-NEXT: [[as_b:%[0-9]+]] = tail call ptr @__dynamic_cast(ptr nonnull %a, ptr nonnull @_ZTI1A, ptr nonnull @_ZTI1B, i64 0)
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// CHECK-NEXT: br label %[[dynamic_cast_end]]
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// CHECK: [[dynamic_cast_end]]:
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// CHECK-NEXT: [[res:%[0-9]+]] = phi ptr [ [[as_b]], %[[dynamic_cast_notnull]] ], [ null, %entry ]
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// CHECK-NEXT: ret ptr [[res]]
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// CHECK-NEXT: }
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// CHECK: declare ptr @__dynamic_cast(ptr, ptr, ptr, i64) local_unnamed_addr
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// CHECK: define{{.*}} ptr @_Z8selfcastP1B(ptr noundef readnone returned %b) local_unnamed_addr
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// CHECK-NEXT: entry
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// CHECK-NEXT: ret ptr %b
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// CHECK-NEXT: }
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// CHECK: define{{.*}} ptr @_Z9void_castP1B(ptr noundef readonly %b) local_unnamed_addr
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// CHECK-NEXT: entry:
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// CHECK-NEXT: [[isnull:%[0-9]+]] = icmp eq ptr %b, null
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// CHECK-NEXT: br i1 [[isnull]], label %[[dynamic_cast_end:[a-z0-9._]+]], label %[[dynamic_cast_notnull:[a-z0-9._]+]]
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// CHECK: [[dynamic_cast_notnull]]:
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// CHECK-DAG: [[vtable:%[a-z0-9]+]] = load ptr, ptr %b, align 8
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// CHECK-DAG: [[offset_ptr:%.+]] = getelementptr inbounds i8, ptr [[vtable]], i64 -8
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// CHECK-DAG: [[offset_to_top:%.+]] = load i32, ptr [[offset_ptr]], align 4
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// CHECK-DAG: [[offset_to_top2:%.+]] = sext i32 [[offset_to_top]] to i64
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// CHECK-DAG: [[casted:%.+]] = getelementptr inbounds i8, ptr %b, i64 [[offset_to_top2]]
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// CHECK-NEXT: br label %[[dynamic_cast_end]]
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// CHECK: [[dynamic_cast_end]]:
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// CHECK-NEXT: [[res:%[0-9]+]] = phi ptr [ [[casted]], %[[dynamic_cast_notnull]] ], [ null, %entry ]
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// CHECK-NEXT: ret ptr [[res]]
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// CHECK-NEXT: }
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class A {
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public:
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virtual void foo();
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};
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class B : public A {
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public:
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void foo() override;
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};
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void A::foo() {}
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void B::foo() {}
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A *upcast(B *b) {
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return dynamic_cast<A *>(b);
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}
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B *downcast(A *a) {
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return dynamic_cast<B *>(a);
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}
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B *selfcast(B *b) {
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return dynamic_cast<B *>(b);
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}
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void *void_cast(B *b) {
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return dynamic_cast<void *>(b);
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}
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