b468ed494a
In 39b2979a4 Pavel has kindly refined the implementation of a test in such a way that it doesn't trip up over this patch -- the test wishes to stimulate LLDBs presentation of line0 locations, rather than wanting to always step on line-zero on entry to artificial_location.c. As that's what was tripping up this change, reapply. Original commit message follows. [DWARF] Emit a worst-case prologue_end flag for pathological inputs (#107849) prologue_end usually indicates where the end of the function-initialization lies, and is where debuggers usually choose to put the initial breakpoint for a function. Our current algorithm piggy-backs it on the first available source-location: which doesn't necessarily have anything to do with the start of the function. To avoid this in heavily-optimised code that lacks many useful source locations, pick a worst-case "if all else fails" prologue_end location, of the first instruction that appears to do meaningful computation. It'll be given the function-scope line number, which should run-on from the start of the function anyway. This means if your code is completely inverted by the optimiser, you can at least put a breakpoint at the _start_ like you expect, even if it's difficult to then step through. This patch also attempts to preserve some good behaviour we have without optimisations -- at O0, if the prologue immediately falls into a loop body without any computation happening, then prologue_end lands at the start of that loop. This is desirable; but does mean we need to do more work to detect and support those situations.
69 lines
2.8 KiB
LLVM
69 lines
2.8 KiB
LLVM
; RUN: llc -O2 %s -o - -mtriple=x86_64-unknown-linux-gnu | FileCheck %s --check-prefix=OPTS
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; RUN: llc -O0 %s -o - -mtriple=x86_64-unknown-linux-gnu | FileCheck %s --check-prefix=UNOPT
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;; Test that, even though there are no source locations attached to the foo
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;; function, we still give it the start-of-function source location of the
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;; definition line. Otherwise, this function would have no entry in the
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;; line table at all.
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; OPTS-LABEL: foo:
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; OPTS-NEXT: .Lfunc_begin0:
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; OPTS-NEXT: .file 0 "." "foobar.c"
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; OPTS-NEXT: .cfi_startproc
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; OPTS-NEXT: # %bb.0:
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; OPTS-NEXT: .loc 0 1 0 prologue_end
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; OPTS-LABEL: bar:
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define dso_local noundef i32 @foo(ptr nocapture noundef writeonly %bar) local_unnamed_addr !dbg !10 {
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entry:
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store i32 0, ptr %bar, align 4
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ret i32 0
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}
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;; In a function with no source location, but multiple blocks, there will be
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;; an opening scope-line. Test for this behaviour, and preserve the
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;; unconditional branch by compiling -O0.
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; UNOPT-LABEL: bar:
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; UNOPT-NEXT: .Lfunc_begin1:
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; UNOPT-NEXT: .cfi_startproc
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; UNOPT-LABEL: %bb.0:
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; UNOPT-NEXT: .loc 0 11 0 prologue_end
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; UNOPT-NEXT: movq %rdi, -8(%rsp)
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; UNOPT-NEXT: jmp .LBB1_1
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; UNOPT-LABEL: .LBB1_1:
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; UNOPT-NEXT: movq -8(%rsp), %rax
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define dso_local noundef i32 @bar(ptr nocapture noundef writeonly %baz) local_unnamed_addr !dbg !20 {
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entry:
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br label %bb1
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bb1:
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store i32 0, ptr %baz, align 4
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ret i32 0
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}
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!2, !3}
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!llvm.ident = !{!9}
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!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
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!1 = !DIFile(filename: "foobar.c", directory: ".")
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!2 = !{i32 7, !"Dwarf Version", i32 5}
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!3 = !{i32 2, !"Debug Info Version", i32 3}
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!9 = !{!"clang"}
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!10 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 1, type: !11, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
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!11 = !DISubroutineType(types: !12)
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!12 = !{!13, !14}
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!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!14 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
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!15 = !{!16}
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!16 = !DILocalVariable(name: "bar", arg: 1, scope: !10, file: !1, line: 1, type: !14)
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!17 = !DILocation(line: 0, scope: !10)
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!18 = !DILocation(line: 2, column: 8, scope: !10)
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!20 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 11, type: !11, scopeLine: 11, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !25)
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!25 = !{!26}
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!26 = !DILocalVariable(name: "bar", arg: 1, scope: !20, file: !1, line: 11, type: !14)
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!27 = !DILocation(line: 0, scope: !20)
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!28 = !DILocation(line: 12, column: 8, scope: !20)
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