[llvm] [DebugInfo] Fix line 0 records incorrectly having is_stmt set (PR #166627)

[Jeremy Morse via llvm-commits]

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@@ -2400,8 +2404,11 @@ DwarfDebug::emitInitialLocDirective(const MachineFunction &MF, unsigned CUID) {
   (void)getOrCreateDwarfCompileUnit(SP->getUnit());
   // We'd like to list the prologue as "not statements" but GDB behaves
   // poorly if we do that. Revisit this with caution/GDB (7.5+) testing.
-  ::recordSourceLine(*Asm, SP->getScopeLine(), 0, SP, DWARF2_FLAG_IS_STMT,
-                     CUID, getDwarfVersion(), getUnits());
+  // However, we should not set is_stmt for line 0.
+  unsigned ScopeLine = SP->getScopeLine();
+  unsigned Flags = (ScopeLine != 0) ? DWARF2_FLAG_IS_STMT : 0;
+  ::recordSourceLine(*Asm, ScopeLine, 0, SP, Flags, CUID, getDwarfVersion(),
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jmorse wrote:

Gut instinct, given that the scope line is directly extracted from the subprogram, is that it can't be a legitimate outcome of optimisation: the scope line is a static property of the source code, not of the program under transformation.

https://github.com/llvm/llvm-project/pull/166627