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.
56 lines
2.7 KiB
LLVM
56 lines
2.7 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt -passes='default<O2>' -S < %s | FileCheck %s
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define void @copy(ptr noalias %to, ptr noalias %from) {
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; CHECK-LABEL: @copy(
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; CHECK-NEXT: [[X:%.*]] = load i32, ptr [[FROM:%.*]], align 4
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; CHECK-NEXT: store i32 [[X]], ptr [[TO:%.*]], align 4
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; CHECK-NEXT: ret void
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;
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%x = load i32, ptr %from
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store i32 %x, ptr %to
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ret void
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}
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; Consider that %addr1 = %addr2 + 1, in which case %addr2i and %addr1i are
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; noalias within one iteration, but may alias across iterations.
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define void @pr39282(ptr %addr1, ptr %addr2) {
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; CHECK-LABEL: @pr39282(
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; CHECK-NEXT: start:
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; CHECK-NEXT: tail call void @llvm.experimental.noalias.scope.decl(metadata [[META0:![0-9]+]])
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; CHECK-NEXT: tail call void @llvm.experimental.noalias.scope.decl(metadata [[META3:![0-9]+]])
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; CHECK-NEXT: [[X_I:%.*]] = load i32, ptr [[ADDR1:%.*]], align 4, !alias.scope !3, !noalias !0
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; CHECK-NEXT: store i32 [[X_I]], ptr [[ADDR2:%.*]], align 4, !alias.scope !0, !noalias !3
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; CHECK-NEXT: [[ADDR1I_1:%.*]] = getelementptr inbounds i8, ptr [[ADDR1]], i64 4
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; CHECK-NEXT: [[ADDR2I_1:%.*]] = getelementptr inbounds i8, ptr [[ADDR2]], i64 4
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; CHECK-NEXT: tail call void @llvm.experimental.noalias.scope.decl(metadata [[META5:![0-9]+]])
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; CHECK-NEXT: tail call void @llvm.experimental.noalias.scope.decl(metadata [[META7:![0-9]+]])
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; CHECK-NEXT: [[X_I_1:%.*]] = load i32, ptr [[ADDR1I_1]], align 4, !alias.scope !7, !noalias !5
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; CHECK-NEXT: store i32 [[X_I_1]], ptr [[ADDR2I_1]], align 4, !alias.scope !5, !noalias !7
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; CHECK-NEXT: tail call void @llvm.experimental.noalias.scope.decl(metadata [[META9:![0-9]+]])
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; CHECK-NEXT: tail call void @llvm.experimental.noalias.scope.decl(metadata [[META11:![0-9]+]])
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; CHECK-NEXT: [[X_I_2:%.*]] = load i32, ptr [[ADDR1]], align 4, !alias.scope !11, !noalias !9
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; CHECK-NEXT: store i32 [[X_I_2]], ptr [[ADDR2]], align 4, !alias.scope !9, !noalias !11
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; CHECK-NEXT: tail call void @llvm.experimental.noalias.scope.decl(metadata [[META13:![0-9]+]])
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; CHECK-NEXT: tail call void @llvm.experimental.noalias.scope.decl(metadata [[META15:![0-9]+]])
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; CHECK-NEXT: [[X_I_3:%.*]] = load i32, ptr [[ADDR1I_1]], align 4, !alias.scope !15, !noalias !13
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; CHECK-NEXT: store i32 [[X_I_3]], ptr [[ADDR2I_1]], align 4, !alias.scope !13, !noalias !15
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; CHECK-NEXT: ret void
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;
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start:
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br label %body
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body:
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%i = phi i32 [ 0, %start ], [ %i.next, %body ]
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%j = and i32 %i, 1
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%addr1i = getelementptr inbounds i32, ptr %addr1, i32 %j
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%addr2i = getelementptr inbounds i32, ptr %addr2, i32 %j
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call void @copy(ptr %addr2i, ptr %addr1i)
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%i.next = add i32 %i, 1
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%cmp = icmp slt i32 %i.next, 4
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br i1 %cmp, label %body, label %end
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end:
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ret void
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}
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