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.
75 lines
2.3 KiB
LLVM
75 lines
2.3 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt < %s -passes=instcombine -S | FileCheck %s
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; Memcpy is copying known-undef, and is thus removable
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define void @test(ptr %dest) {
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; CHECK-LABEL: @test(
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; CHECK-NEXT: ret void
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;
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%a = alloca [7 x i8]
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call void @llvm.memcpy.p0.p0.i64(ptr %dest, ptr %a, i64 7, i1 false)
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ret void
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}
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; Some non-undef elements
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define void @test2(ptr %dest) {
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; CHECK-LABEL: @test2(
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; CHECK-NEXT: [[A:%.*]] = alloca [7 x i8], align 1
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; CHECK-NEXT: store i8 0, ptr [[A]], align 1
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; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 1 dereferenceable(7) [[DEST:%.*]], ptr noundef nonnull align 1 dereferenceable(7) [[A]], i64 7, i1 false)
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; CHECK-NEXT: ret void
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;
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%a = alloca [7 x i8]
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store i8 0, ptr %a
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call void @llvm.memcpy.p0.p0.i64(ptr %dest, ptr %a, i64 7, i1 false)
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ret void
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}
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; Volatile write is still required
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define void @test3(ptr %dest) {
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; CHECK-LABEL: @test3(
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; CHECK-NEXT: [[A:%.*]] = alloca [7 x i8], align 1
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; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr [[DEST:%.*]], ptr [[A]], i64 7, i1 true)
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; CHECK-NEXT: ret void
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;
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%a = alloca [7 x i8]
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call void @llvm.memcpy.p0.p0.i64(ptr %dest, ptr %a, i64 7, i1 true)
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ret void
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}
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define void @test4(ptr %dest) {
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; CHECK-LABEL: @test4(
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; CHECK-NEXT: ret void
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;
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%a = alloca [7 x i8]
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call void @llvm.memcpy.p0.p0.i64(ptr %dest, ptr %a, i64 7, i1 false)
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ret void
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}
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define void @test5(ptr %dest) {
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; CHECK-LABEL: @test5(
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; CHECK-NEXT: ret void
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;
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%a = alloca [7 x i8]
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%p2 = getelementptr i32, ptr %a, i32 1
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call void @llvm.memcpy.p0.p0.i64(ptr %dest, ptr %p2, i64 3, i1 false)
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ret void
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}
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define void @test6(ptr %dest) {
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; CHECK-LABEL: @test6(
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; CHECK-NEXT: [[A:%.*]] = alloca [7 x i8], align 1
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; CHECK-NEXT: [[P2:%.*]] = getelementptr inbounds i8, ptr [[A]], i64 2
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; CHECK-NEXT: store i16 42, ptr [[P2]], align 2
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; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 1 dereferenceable(7) [[DEST:%.*]], ptr noundef nonnull align 1 dereferenceable(7) [[P2]], i64 7, i1 false)
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; CHECK-NEXT: ret void
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;
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%a = alloca [7 x i8]
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%p2 = getelementptr i16, ptr %a, i32 1
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store i16 42, ptr %p2
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call void @llvm.memcpy.p0.p0.i64(ptr %dest, ptr %p2, i64 7, i1 false)
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ret void
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}
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declare void @llvm.memcpy.p0.p0.i64(ptr, ptr, i64, i1)
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