[llvm] r223193 - Emit the entry block first and the exit block second, then all the blocks in between afterwards. This is what gcc always does, and some out of tree tools depend on that.
Nick Lewycky
nicholas at mxc.ca
Mon Mar 9 21:38:35 PDT 2015
Justin Bogner wrote:
> Nick Lewycky<nicholas at mxc.ca> writes:
>> Author: nicholas
>> Date: Tue Dec 2 20:45:01 2014
>> New Revision: 223193
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=223193&view=rev
>> Log:
>> Emit the entry block first and the exit block second, then all the
>> blocks in between afterwards. This is what gcc always does, and some
>> out of tree tools depend on that.
>
> Sorry I didn't notice this earlier, but there's something funny going on
> here. This makes llvm-cov choke on a simple hello world, as it assumes
> that "The last block is always reserved for exit block".
>
> Now, if gcc always emits the exit block second, this assumption makes no
> sense, in which case I'll fix up llvm-cov. However, it looks like this
> assumption did make sense back in the gcov-4.2 era, which warns that
> each function "has arcs from exit block" with this change. I'm guessing
> this behaviour changed (from "last" to "second") in some update of the
> format, and that we should not be doing this when emitting a format
> version of "402*".
>
> Do you have any insight into this?
I don't, besides noticing that it comes second instead of last in gcc
4.7. If gcc 4.2 put is last, then we'll need a flag to switch between
the two behaviours.
Nick
>
>> Added:
>> llvm/trunk/test/Transforms/GCOVProfiling/return-block.ll
>> Modified:
>> llvm/trunk/lib/Transforms/Instrumentation/GCOVProfiling.cpp
>>
>> Modified: llvm/trunk/lib/Transforms/Instrumentation/GCOVProfiling.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Instrumentation/GCOVProfiling.cpp?rev=223193&r1=223192&r2=223193&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Instrumentation/GCOVProfiling.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Instrumentation/GCOVProfiling.cpp Tue Dec 2 20:45:01 2014
>> @@ -310,11 +310,15 @@ namespace {
>>
>> Function *F = SP.getFunction();
>> DEBUG(dbgs()<< "Function: "<< getFunctionName(SP)<< "\n");
>> - uint32_t i = 0;
>> - for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
>> +
>> + Function::iterator BB = F->begin(), E = F->end();
>> + Blocks[BB++] = new GCOVBlock(0, os);
>> + ReturnBlock = new GCOVBlock(1, os);
>> +
>> + uint32_t i = 2;
>> + for (; BB != E; ++BB) {
>> Blocks[BB] = new GCOVBlock(i++, os);
>> }
>> - ReturnBlock = new GCOVBlock(i++, os);
>>
>> std::string FunctionNameAndLine;
>> raw_string_ostream FNLOS(FunctionNameAndLine);
>>
>> Added: llvm/trunk/test/Transforms/GCOVProfiling/return-block.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GCOVProfiling/return-block.ll?rev=223193&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/GCOVProfiling/return-block.ll (added)
>> +++ llvm/trunk/test/Transforms/GCOVProfiling/return-block.ll Tue Dec 2 20:45:01 2014
>> @@ -0,0 +1,66 @@
>> +; Inject metadata to set the .gcno file location
>> +; RUN: echo '!19 = metadata !{metadata !"%/T/return-block.ll", metadata !0}'> %t1
>> +; RUN: cat %s %t1> %t2
>> +; RUN: opt -insert-gcov-profiling -disable-output %t2
>> +; RUN: llvm-cov gcov -n -dump return-block.gcno 2>&1 | FileCheck %s
>> +
>> +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
>> +target triple = "x86_64-unknown-linux-gnu"
>> +
>> + at A = common global i32 0, align 4
>> +
>> +; Function Attrs: nounwind uwtable
>> +define void @test() #0 {
>> +entry:
>> + tail call void (...)* @f() #2, !dbg !14
>> + %0 = load i32* @A, align 4, !dbg !15
>> + %tobool = icmp eq i32 %0, 0, !dbg !15
>> + br i1 %tobool, label %if.end, label %if.then, !dbg !15
>> +
>> +if.then: ; preds = %entry
>> + tail call void (...)* @g() #2, !dbg !16
>> + br label %if.end, !dbg !16
>> +
>> +if.end: ; preds = %entry, %if.then
>> + ret void, !dbg !18
>> +}
>> +
>> +declare void @f(...) #1
>> +
>> +declare void @g(...) #1
>> +
>> +attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
>> +attributes #1 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
>> +attributes #2 = { nounwind }
>> +
>> +!llvm.gcov = !{!14}
>> +!llvm.dbg.cu = !{!0}
>> +!llvm.module.flags = !{!11, !12}
>> +!llvm.ident = !{!13}
>> +
>> +!0 = metadata !{metadata !"0x11\0012\00clang version 3.6.0 (trunk 223182)\001\00\000\00\001", metadata !1, metadata !2, metadata !2, metadata !3, metadata !8, metadata !2} ; [ DW_TAG_compile_unit ] [return-block.c] [DW_LANG_C99]
>> +!1 = metadata !{metadata !".../llvm/test/Transforms/GCOVProfiling/return-block.ll", metadata !""}
>> +!2 = metadata !{}
>> +!3 = metadata !{metadata !4}
>> +!4 = metadata !{metadata !"0x2e\00test\00test\00\005\000\001\000\000\000\001\005", metadata !1, metadata !5, metadata !6, null, void ()* @test, null, null, metadata !2} ; [ DW_TAG_subprogram ] [line 5] [def] [test]
>> +!5 = metadata !{metadata !"0x29", metadata !1} ; [ DW_TAG_file_type ] [return-block.c]
>> +!6 = metadata !{metadata !"0x15\00\000\000\000\000\000\000", null, null, null, metadata !7, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
>> +!7 = metadata !{null}
>> +!8 = metadata !{metadata !9}
>> +!9 = metadata !{metadata !"0x34\00A\00A\00\003\000\001", null, metadata !5, metadata !10, i32* @A, null} ; [ DW_TAG_variable ] [A] [line 3] [def]
>> +!10 = metadata !{metadata !"0x24\00int\000\0032\0032\000\000\005", null, null} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
>> +!11 = metadata !{i32 2, metadata !"Dwarf Version", i32 4}
>> +!12 = metadata !{i32 2, metadata !"Debug Info Version", i32 2}
>> +!13 = metadata !{metadata !"clang version 3.6.0 (trunk 223182)"}
>> +!14 = metadata !{i32 6, i32 3, metadata !4, null}
>> +!15 = metadata !{i32 7, i32 7, metadata !4, null}
>> +!16 = metadata !{i32 8, i32 5, metadata !17, null}
>> +!17 = metadata !{metadata !"0xb\007\007\000", metadata !1, metadata !4} ; [ DW_TAG_lexical_block ] [return-block.c]
>> +!18 = metadata !{i32 9, i32 1, metadata !4, null}
>> +
>> +; There should be no destination edges for block 1.
>> +; CHECK: Block : 0 Counter : 0
>> +; CHECK-NEXT: Destination Edges : 2 (0),
>> +; CHECK-NEXT: Block : 1 Counter : 0
>> +; CHECK-NEXT: Source Edges : 4 (0),
>> +; CHECK-NEXT: Block : 2 Counter : 0
>>
>>
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