ddf1864ace
Add an IR phase right before main module optimization.
This is to modify IR to restrict certain downward optimizations
in order to generate verifier friendly code.
> prevent certain instcombine optimizations, handling both
in-block/cross-block instcombines.
> avoid speculative code motion if the variable used in
condition is also used in the later blocks.
Internally, a bpf IR builtin
result = __builtin_bpf_passthrough(seq_num, result)
is used to enforce ordering. This builtin is only used
during target independent IR optimizations and it will
be removed at the beginning of target dependent IR
optimizations.
For example, removing the following workaround,
--- a/tools/testing/selftests/bpf/progs/test_sysctl_loop1.c
+++ b/tools/testing/selftests/bpf/progs/test_sysctl_loop1.c
@@ -47,7 +47,7 @@ int sysctl_tcp_mem(struct bpf_sysctl *ctx)
/* a workaround to prevent compiler from generating
* codes verifier cannot handle yet.
*/
- volatile int ret;
+ int ret;
this patch is able to generate code which passed the verifier.
To disable optimization, users need to use "opt" command like below:
clang -target bpf -O2 -S -emit-llvm -Xclang -disable-llvm-passes test.c
// disable icmp serialization
opt -O2 -bpf-disable-serialize-icmp test.ll | llvm-dis > t.ll
// disable avoid-speculation
opt -O2 -bpf-disable-avoid-speculation test.ll | llvm-dis > t.ll
llc t.ll
Differential Revision: https://reviews.llvm.org/D85570
85 lines
3.3 KiB
LLVM
85 lines
3.3 KiB
LLVM
; RUN: opt -O2 -mtriple=bpf-pc-linux %s | llvm-dis > %t1
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; RUN: llc %t1 -o - | FileCheck -check-prefixes=CHECK-COMMON,CHECK %s
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; RUN: opt -O2 -mtriple=bpf-pc-linux -bpf-disable-avoid-speculation %s | llvm-dis > %t1
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; RUN: llc %t1 -o - | FileCheck -check-prefixes=CHECK-COMMON,CHECK-DISABLE %s
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;
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; Source:
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; unsigned long foo();
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; void *test(void *p) {
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; unsigned long ret = foo();
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; if (ret <= 7)
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; p += ret;
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; return p;
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; }
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; Compilation flag:
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; clang -target bpf -O2 -S -emit-llvm -Xclang -disable-llvm-passes test.c
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; Function Attrs: nounwind
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define dso_local i8* @test(i8* %p) #0 {
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entry:
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%p.addr = alloca i8*, align 8
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%ret = alloca i64, align 8
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store i8* %p, i8** %p.addr, align 8, !tbaa !2
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%0 = bitcast i64* %ret to i8*
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call void @llvm.lifetime.start.p0i8(i64 8, i8* %0) #3
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%call = call i64 bitcast (i64 (...)* @foo to i64 ()*)()
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store i64 %call, i64* %ret, align 8, !tbaa !6
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%1 = load i64, i64* %ret, align 8, !tbaa !6
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%cmp = icmp ule i64 %1, 7
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br i1 %cmp, label %if.then, label %if.end
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if.then: ; preds = %entry
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%2 = load i64, i64* %ret, align 8, !tbaa !6
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%3 = load i8*, i8** %p.addr, align 8, !tbaa !2
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%add.ptr = getelementptr i8, i8* %3, i64 %2
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store i8* %add.ptr, i8** %p.addr, align 8, !tbaa !2
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br label %if.end
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if.end: ; preds = %if.then, %entry
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%4 = load i8*, i8** %p.addr, align 8, !tbaa !2
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%5 = bitcast i64* %ret to i8*
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call void @llvm.lifetime.end.p0i8(i64 8, i8* %5) #3
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ret i8* %4
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}
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; CHECK-COMMON: [[REG6:r[0-9]+]] = r1
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; CHECK-COMMON: call foo
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; CHECK: if r0 > 7 goto [[LABEL:.*]]
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; CHECK: [[REG6]] += r0
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; CHECK: [[LABEL]]:
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; CHECK: r0 = [[REG6]]
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; CHECK-DISABLE: r0 = [[REG6]]
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; CHECK-DISABLE: r0 += [[REG1:r[0-9]+]]
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; CHECK-DISABLE: [[REG2:r[0-9]+]] = 8
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; CHECK-DISABLE: if [[REG2]] > [[REG1]] goto [[LABEL:.*]]
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; CHECK-DISABLE: r0 = [[REG6]]
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; CHECK-DISABLE: [[LABEL]]:
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; CHECK-COMMON: exit
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; Function Attrs: argmemonly nounwind willreturn
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declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1
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declare dso_local i64 @foo(...) #2
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; Function Attrs: argmemonly nounwind willreturn
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declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1
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attributes #0 = { nounwind "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
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attributes #1 = { argmemonly nounwind willreturn }
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attributes #2 = { "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
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attributes #3 = { nounwind }
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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 version 12.0.0 (https://github.com/llvm/llvm-project.git ca9c5433a6c31e372092fcd8bfd0e4fddd7e8784)"}
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!2 = !{!3, !3, i64 0}
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!3 = !{!"any pointer", !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 = !{!7, !7, i64 0}
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!7 = !{!"long", !4, i64 0}
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