[llvm] 795bbb3 - [BPF] fix a bug in BPFMISimplifyPatchable pass with -O0

Thu Jan 30 13:17:52 PST 2020

On 1/30/20 1:13 PM, Tom Stellard wrote:
> On 01/30/2020 08:29 AM, Yonghong Song via llvm-commits wrote:
>>
>> Author: Yonghong Song
>> Date: 2020-01-30T08:28:39-08:00
>> New Revision: 795bbb366266e83d2bea8dc04c19919b52ab3a2a
>>
> 
> Is this something we should backport to the 10.0 branch?

Yes. I actually plan to file a bug (blocking master bug 
https://llvm.org/pr44555) later. I have tested on the 10.0 release 
branch. The patch can
be taken as is and all tests should pass.

Thanks for asking!

> 
> -Tom
> 
>> URL: https://github.com/llvm/llvm-project/commit/795bbb366266e83d2bea8dc04c19919b52ab3a2a
>> DIFF: https://github.com/llvm/llvm-project/commit/795bbb366266e83d2bea8dc04c19919b52ab3a2a.diff
>>
>> LOG: [BPF] fix a bug in BPFMISimplifyPatchable pass with -O0
>>
>> The recommended optimization level for BPF programs
>> is O2 since (1). BPF is running inside the kernel and
>> linux kernel won't work at -O0 level, and (2). Verifier
>> is not able to handle O0 code properly, e.g., potential
>> large stack size and a lot of spills.
>>
>> But we should keep -O0 at least compiling.
>> This patch fixed a bug in BPFMISimplifyPatchable phase
>> where with -O0, a segmentation fault will happen for a
>> simple program like:
>>    int test(int a, int b) { return a + b; }
>>
>> A test case is added to capture such a case.
>>
>> Differential Revision: https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D73681&d=DwICaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=EtUNePv4QI8UexDkXydyw_hN936uo6_EWixV_VuEGe4&s=EVKCtdrIJIRhI5QwTx2u56JGoh7a5oMDpPUFNb9ouPg&e=
>>
>> Added:
>>      llvm/test/CodeGen/BPF/optnone-1.ll
>>
>> Modified:
>>      llvm/lib/Target/BPF/BPFMISimplifyPatchable.cpp
>>
>> Removed:
>>      
>>
>>
>> ################################################################################
>> diff  --git a/llvm/lib/Target/BPF/BPFMISimplifyPatchable.cpp b/llvm/lib/Target/BPF/BPFMISimplifyPatchable.cpp
>> index 5310f0f07b65..29abc9303a62 100644
>> --- a/llvm/lib/Target/BPF/BPFMISimplifyPatchable.cpp
>> +++ b/llvm/lib/Target/BPF/BPFMISimplifyPatchable.cpp
>> @@ -70,9 +70,10 @@ struct BPFMISimplifyPatchable : public MachineFunctionPass {
>>   public:
>>     // Main entry point for this pass.
>>     bool runOnMachineFunction(MachineFunction &MF) override {
>> -    if (!skipFunction(MF.getFunction())) {
>> -      initialize(MF);
>> -    }
>> +    if (skipFunction(MF.getFunction()))
>> +      return false;
>> +
>> +    initialize(MF);
>>       return removeLD();
>>     }
>>   };
>>
>> diff  --git a/llvm/test/CodeGen/BPF/optnone-1.ll b/llvm/test/CodeGen/BPF/optnone-1.ll
>> new file mode 100644
>> index 000000000000..b38e2630ff28
>> --- /dev/null
>> +++ b/llvm/test/CodeGen/BPF/optnone-1.ll
>> @@ -0,0 +1,52 @@
>> +; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
>> +; Source Code:
>> +;   int test(int a, int b) { return a + b; }
>> +; Compilation flag:
>> +;   clang -target bpf -g -S -emit-llvm test.c
>> +
>> +; Function Attrs: noinline nounwind optnone
>> +define dso_local i32 @test(i32 %a, i32 %b) #0 !dbg !7 {
>> +entry:
>> +  %a.addr = alloca i32, align 4
>> +  %b.addr = alloca i32, align 4
>> +  store i32 %a, i32* %a.addr, align 4
>> +  call void @llvm.dbg.declare(metadata i32* %a.addr, metadata !11, metadata !DIExpression()), !dbg !12
>> +  store i32 %b, i32* %b.addr, align 4
>> +  call void @llvm.dbg.declare(metadata i32* %b.addr, metadata !13, metadata !DIExpression()), !dbg !14
>> +  %0 = load i32, i32* %a.addr, align 4, !dbg !15
>> +  %1 = load i32, i32* %b.addr, align 4, !dbg !16
>> +  %add = add nsw i32 %0, %1, !dbg !17
>> +  ret i32 %add, !dbg !18
>> +}
>> +
>> +; CHECK-LABEL: test
>> +
>> +; Function Attrs: nounwind readnone speculatable
>> +declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
>> +
>> +attributes #0 = { noinline nounwind optnone "correctly-rounded-divide-sqrt-fp-math"="false" "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"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
>> +attributes #1 = { nounwind readnone speculatable}
>> +
>> +!llvm.dbg.cu = !{!0}
>> +!llvm.module.flags = !{!3, !4, !5}
>> +!llvm.ident = !{!6}
>> +
>> +!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.0 (https://github.com/llvm/llvm-project.git 7f49dc496682e38335b204bbae371a0ca5057719)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
>> +!1 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/llvm")
>> +!2 = !{}
>> +!3 = !{i32 7, !"Dwarf Version", i32 4}
>> +!4 = !{i32 2, !"Debug Info Version", i32 3}
>> +!5 = !{i32 1, !"wchar_size", i32 4}
>> +!6 = !{!"clang version 11.0.0 (https://github.com/llvm/llvm-project.git 7f49dc496682e38335b204bbae371a0ca5057719)"}
>> +!7 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
>> +!8 = !DISubroutineType(types: !9)
>> +!9 = !{!10, !10, !10}
>> +!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
>> +!11 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 1, type: !10)
>> +!12 = !DILocation(line: 1, column: 14, scope: !7)
>> +!13 = !DILocalVariable(name: "b", arg: 2, scope: !7, file: !1, line: 1, type: !10)
>> +!14 = !DILocation(line: 1, column: 21, scope: !7)
>> +!15 = !DILocation(line: 1, column: 33, scope: !7)
>> +!16 = !DILocation(line: 1, column: 37, scope: !7)
>> +!17 = !DILocation(line: 1, column: 35, scope: !7)
>> +!18 = !DILocation(line: 1, column: 26, scope: !7)
>>
>>
>>          
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>>
> 