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.
86 lines
2.7 KiB
LLVM
86 lines
2.7 KiB
LLVM
; RUN: opt -O2 -mtriple=bpf-pc-linux -S -o - %s | FileCheck %s
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;
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; Check position of bpf-preserve-static-offset pass in the pipeline:
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; - preserve.static.offset call is preserved if address is passed as
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; a parameter to an inline-able function;
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; - second bpf-preserve-static-offset pass (after inlining) should introduce
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; getelementptr.and.load call using the preserved marker.
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;
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; Source:
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; #define __ctx __attribute__((preserve_static_offset))
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;
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; struct bar {
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; int aa;
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; int bb;
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; };
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;
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; struct foo {
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; int a;
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; struct bar b;
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; } __ctx;
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;
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; extern void consume(int);
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;
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; static inline void bar(struct bar *p){
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; consume(p->bb);
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; }
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;
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; void quux(struct foo *p) {
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; bar(&p->b);
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; }
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;
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; Compilation flag:
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; clang -cc1 -O2 -triple bpf -S -emit-llvm -disable-llvm-passes -o - \
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; | opt -passes=function(sroa) -S -o -
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%struct.foo = type { i32, %struct.bar }
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%struct.bar = type { i32, i32 }
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; Function Attrs: nounwind
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define dso_local void @quux(ptr noundef %p) #0 {
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entry:
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%0 = call ptr @llvm.preserve.static.offset(ptr %p)
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%b = getelementptr inbounds %struct.foo, ptr %0, i32 0, i32 1
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call void @bar(ptr noundef %b)
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ret void
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}
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; Function Attrs: inlinehint nounwind
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define internal void @bar(ptr noundef %p) #1 {
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entry:
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%bb = getelementptr inbounds %struct.bar, ptr %p, i32 0, i32 1
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%0 = load i32, ptr %bb, align 4, !tbaa !2
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call void @consume(i32 noundef %0)
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ret void
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}
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; CHECK: define dso_local void @quux(ptr nocapture noundef readonly %[[p:.*]])
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; CHECK: %[[bb_i1:.*]] = tail call i32 (ptr, i1, i8, i8, i8, i1, ...)
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; CHECK-SAME: @llvm.bpf.getelementptr.and.load.i32
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; CHECK-SAME: (ptr readonly elementtype(i8) %[[p]],
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; CHECK-SAME: i1 false, i8 0, i8 1, i8 2, i1 true, i64 immarg 8)
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; CHECK-SAME: #[[v2:.*]], !tbaa
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; CHECK-NEXT: tail call void @consume(i32 noundef %[[bb_i1]])
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; CHECK: attributes #[[v2]] = { memory(argmem: read) }
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; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
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declare ptr @llvm.preserve.static.offset(ptr readnone) #2
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declare void @consume(i32 noundef) #3
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attributes #0 = { nounwind "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
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attributes #1 = { inlinehint nounwind "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
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attributes #2 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
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attributes #3 = { "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
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!llvm.module.flags = !{!0}
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!llvm.ident = !{!1}
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!0 = !{i32 1, !"wchar_size", i32 4}
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!1 = !{!"clang"}
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!2 = !{!3, !4, i64 4}
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!3 = !{!"bar", !4, i64 0, !4, i64 4}
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!4 = !{!"int", !5, i64 0}
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!5 = !{!"omnipotent char", !6, i64 0}
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!6 = !{!"Simple C/C++ TBAA"}
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