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c03bf16516
Commit a0841dfe8594 ("[BPF] Fix a bug in peephole optimization")
fixed a bug in peephole optimization. Recursion is introduced
to handle COPY and PHI instructions.
Unfortunately, multiple PHI instructions may form a cycle
and this will cause infinite recursion, eventual segfault.
For Commit a0841dfe8594, I indeed tried a few loops to ensure
that I won't see the recursion, but I did not try with
complex control flows, which, as demonstrated with the test case
in this patch, may introduce PHI cycles.
This patch fixed the issue by introducing a set to remember
visited PHI instructions. This way, cycles can be properly
detected and handled.
Differential Revision: https://reviews.llvm.org/D70586
53 lines
1.6 KiB
LLVM
53 lines
1.6 KiB
LLVM
; RUN: llc -O2 -march=bpfel -mcpu=v2 -mattr=+alu32 < %s | FileCheck %s
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;
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; For the below example, two phi node in the loop may depend on
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; each other. So implementation must handle recursion properly.
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;
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; int test(unsigned long a, unsigned long b, unsigned long c) {
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; int val = 0;
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;
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; #pragma clang loop unroll(disable)
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; for (long i = 0; i < 100; i++) {
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; if (a > b)
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; val = 1;
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; a += b;
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; if (b > c)
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; val = 1;
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; b += c;
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; }
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;
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; return val == 0 ? 1 : 0;
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; }
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define dso_local i32 @test(i64 %a, i64 %b, i64 %c) local_unnamed_addr {
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entry:
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br label %for.body
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for.cond.cleanup: ; preds = %for.body
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%cmp6 = icmp eq i32 %val.2, 0
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%cond = zext i1 %cmp6 to i32
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ret i32 %cond
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for.body: ; preds = %for.body, %entry
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%i.018 = phi i64 [ 0, %entry ], [ %inc, %for.body ]
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%val.017 = phi i32 [ 0, %entry ], [ %val.2, %for.body ]
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%a.addr.016 = phi i64 [ %a, %entry ], [ %add, %for.body ]
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%b.addr.015 = phi i64 [ %b, %entry ], [ %add5, %for.body ]
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%cmp1 = icmp ugt i64 %a.addr.016, %b.addr.015
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%add = add i64 %a.addr.016, %b.addr.015
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%cmp2 = icmp ugt i64 %b.addr.015, %c
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%0 = or i1 %cmp2, %cmp1
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%val.2 = select i1 %0, i32 1, i32 %val.017
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%add5 = add i64 %b.addr.015, %c
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%inc = add nuw nsw i64 %i.018, 1
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%exitcond = icmp eq i64 %inc, 100
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br i1 %exitcond, label %for.cond.cleanup, label %for.body, !llvm.loop !2
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}
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; CHECK: [[VAL:r[0-9]+]] <<= 32
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; CHECK: [[VAL]] >>= 32
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; CHECK: if [[VAL]] == 0 goto
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!2 = distinct !{!2, !3}
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!3 = !{!"llvm.loop.unroll.disable"}
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