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.
96 lines
3.5 KiB
LLVM
96 lines
3.5 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 should be preserved long enough to allow
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; introduction of getelementptr.and.load after loops unrolling.
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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 foo {
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; int a;
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; int b[4];
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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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; void bar(struct foo *p){
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; unsigned long i = 0;
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; #pragma clang loop unroll(full)
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; while (i < 2)
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; consume(p->b[i++]);
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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, [4 x i32] }
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; Function Attrs: nounwind
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define dso_local void @bar(ptr noundef %p) #0 {
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entry:
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br label %while.cond
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while.cond: ; preds = %while.body, %entry
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%i.0 = phi i64 [ 0, %entry ], [ %inc, %while.body ]
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%cmp = icmp ult i64 %i.0, 2
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br i1 %cmp, label %while.body, label %while.end
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while.body: ; preds = %while.cond
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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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%inc = add i64 %i.0, 1
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%arrayidx = getelementptr inbounds [4 x i32], ptr %b, i64 0, i64 %i.0
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%1 = load i32, ptr %arrayidx, align 4, !tbaa !2
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call void @consume(i32 noundef %1)
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br label %while.cond, !llvm.loop !6
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while.end: ; preds = %while.cond
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ret void
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}
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; CHECK: define dso_local void @bar(ptr nocapture noundef readonly %[[p:.*]])
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; CHECK: %[[v1:.*]] = 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 4)
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; CHECK-SAME: #[[attrs:.*]], !tbaa
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; CHECK-NEXT: tail call void @consume(i32 noundef %[[v1]])
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; CHECK-NEXT: %[[v2:.*]] = 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: #[[attrs]], !tbaa
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; CHECK-NEXT: tail call void @consume(i32 noundef %[[v2]])
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; CHECK: attributes #[[attrs]] = { memory(argmem: read) }
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; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
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declare void @llvm.lifetime.start.p0(i64 immarg, ptr nocapture) #1
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declare void @consume(i32 noundef) #2
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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) #3
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; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
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declare void @llvm.lifetime.end.p0(i64 immarg, ptr nocapture) #1
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attributes #0 = { nounwind "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
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attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
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attributes #2 = { "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
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attributes #3 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
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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, !3, i64 0}
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!3 = !{!"int", !4, i64 0}
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!4 = !{!"omnipotent char", !5, i64 0}
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!5 = !{!"Simple C/C++ TBAA"}
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!6 = distinct !{!6, !7, !8}
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!7 = !{!"llvm.loop.mustprogress"}
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!8 = !{!"llvm.loop.unroll.full"}
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