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.
57 lines
2.3 KiB
LLVM
57 lines
2.3 KiB
LLVM
; RUN: llc %s --filetype=obj -o %t
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; RUN: llvm-objdump -d %t | FileCheck %s --check-prefixes=OBJ
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; RUN: llvm-dwarfdump --debug-line %t | FileCheck %s --check-prefixes=DBG
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; RUN: llc %s -o - | FileCheck %s --check-prefixes=ASM
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; OBJ: 1:{{.*}}nop
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;; prologue_end goes on start-of-loop, the call to @g.
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;; Address Line Column File ISA Discriminator OpIndex Flags
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; DBG: 0x0000000000000000 3 0 0 0 0 0 is_stmt
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; DBG: 0x0000000000000001 0 0 0 0 0 0
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; DBG: 0x0000000000000010 5 0 0 0 0 0 is_stmt prologue_end
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; DBG: 0x0000000000000017 5 0 0 0 0 0 is_stmt end_sequence
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; ASM: .loc 0 0 0 is_stmt 0
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; ASM-NEXT: .L{{.*}}:
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; ASM-NEXT: .p2align 4
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;; $ cat test.cpp
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;; void g();
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;; void f() {
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;; [[clang::code_align(16)]]
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;; while (1) { g(); }
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;; }
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target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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define dso_local void @f() local_unnamed_addr !dbg !9 {
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entry:
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br label %while.body, !dbg !12
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while.body: ; preds = %entry, %while.body
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tail call void @g(), !dbg !12
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br label %while.body, !dbg !12, !llvm.loop !13
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}
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declare !dbg !16 void @g() local_unnamed_addr
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!2, !3}
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!llvm.ident = !{!8}
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!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 19.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: LineTablesOnly, splitDebugInlining: false, nameTableKind: None)
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!1 = !DIFile(filename: "test.cpp", 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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!8 = !{!"clang version 19.0.0git"}
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!9 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 3, type: !10, scopeLine: 3, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0)
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!10 = !DISubroutineType(types: !11)
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!11 = !{}
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!12 = !DILocation(line: 5, scope: !9)
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!13 = distinct !{!13, !12, !12, !14, !15}
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!14 = !{!"llvm.loop.mustprogress"}
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!15 = !{!"llvm.loop.align", i32 16}
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!16 = !DISubprogram(name: "g", scope: !1, file: !1, line: 2, type: !10, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized)
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