Revert2 "[DebugInfo][DWARF] Set is_stmt on first non-line-0 instruction in BB (#105524)"

Reverted due to large .debug_line size regressions for some
configurations; work currently in place to improve the output of this
behaviour in PR #108251.

This patch also modifies two tests that were created or modified after
the original commit landed and are affected by the revert:

  llvm/test/CodeGen/X86/pseudo_cmov_lower2.ll
  llvm/test/DebugInfo/X86/empty-line-info.ll

This reverts commit 5fef40c.

Author: SLTozer

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -2061,8 +2061,10 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
   unsigned LastAsmLine =
       Asm->OutStreamer->getContext().getCurrentDwarfLoc().getLine();
 
-  bool PrevInstInDiffBB = PrevInstBB && PrevInstBB != MI->getParent();
-  if (DL == PrevInstLoc && !PrevInstInDiffBB) {
+  bool PrevInstInSameSection =
+      (!PrevInstBB ||
+       PrevInstBB->getSectionID() == MI->getParent()->getSectionID());
+  if (DL == PrevInstLoc && PrevInstInSameSection) {
     // If we have an ongoing unspecified location, nothing to do here.
     if (!DL)
       return;
@@ -2091,7 +2093,8 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
     //   possibly debug information; we want it to have a source location.
     // - Instruction is at the top of a block; we don't want to inherit the
     //   location from the physically previous (maybe unrelated) block.
-    if (UnknownLocations == Enable || PrevLabel || PrevInstInDiffBB) {
+    if (UnknownLocations == Enable || PrevLabel ||
+        (PrevInstBB && PrevInstBB != MI->getParent())) {
       // Preserve the file and column numbers, if we can, to save space in
       // the encoded line table.
       // Do not update PrevInstLoc, it remembers the last non-0 line.
@@ -2116,11 +2119,9 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
     PrologEndLoc = nullptr;
   }
   // If the line changed, we call that a new statement; unless we went to
-  // line 0 and came back, in which case it is not a new statement. We also
-  // mark is_stmt for the first non-0 line in each BB, in case a predecessor BB
-  // ends with a different line.
+  // line 0 and came back, in which case it is not a new statement.
   unsigned OldLine = PrevInstLoc ? PrevInstLoc.getLine() : LastAsmLine;
-  if (DL.getLine() && (DL.getLine() != OldLine || PrevInstInDiffBB))
+  if (DL.getLine() && DL.getLine() != OldLine)
     Flags |= DWARF2_FLAG_IS_STMT;
 
   const MDNode *Scope = DL.getScope();

llvm/test/CodeGen/Thumb2/pr52817.ll

@@ -24,7 +24,6 @@ define i32 @test(ptr %arg, ptr %arg1, ptr %arg2) #0 !dbg !6 {
 ; CHECK-NEXT:    movs r3, #0
 ; CHECK-NEXT:  LBB0_1: @ %bb3
 ; CHECK-NEXT:    @ =>This Inner Loop Header: Depth=1
-; CHECK-NEXT:    .loc 1 0 0 is_stmt 0 @ :0:0
 ; CHECK-NEXT:    adds r5, r3, #1
 ; CHECK-NEXT:    str.w lr, [r2]
 ; CHECK-NEXT:    cmp.w lr, #0
@@ -37,7 +36,7 @@ define i32 @test(ptr %arg, ptr %arg1, ptr %arg2) #0 !dbg !6 {
 ; CHECK-NEXT:    movne r6, #0
 ; CHECK-NEXT:  Ltmp0:
 ; CHECK-NEXT:    @DEBUG_VALUE: test:this <- [DW_OP_LLVM_arg 0, DW_OP_plus_uconst 135168, DW_OP_LLVM_arg 1, DW_OP_constu 4, DW_OP_mul, DW_OP_plus, DW_OP_plus_uconst 4, DW_OP_stack_value] $r0, $r5
-; CHECK-NEXT:    .loc 1 28 24 prologue_end is_stmt 1 @ test.cpp:28:24
+; CHECK-NEXT:    .loc 1 28 24 prologue_end @ test.cpp:28:24
 ; CHECK-NEXT:    strne.w r6, [r8]
 ; CHECK-NEXT:    moveq r6, #1
 ; CHECK-NEXT:    ldr r4, [r4, #4]

llvm/test/CodeGen/X86/fsafdo_test1.ll

@@ -4,9 +4,9 @@
 ; Check that fs-afdo discriminators are generated.
 ; V01: .loc    1 7 3 is_stmt 0 discriminator 2 # foo.c:7:3
 ; V01: .loc    1 9 5 is_stmt 1 discriminator 2 # foo.c:9:5
-; V0: .loc    1 9 5 is_stmt 1 discriminator 11266 # foo.c:9:5
+; V0: .loc    1 9 5 discriminator 11266 # foo.c:9:5
 ; V0: .loc    1 7 3 is_stmt 1 discriminator 11266 # foo.c:7:3
-; V1: .loc    1 9 5 is_stmt 1 discriminator 514 # foo.c:9:5
+; V1: .loc    1 9 5 discriminator 514 # foo.c:9:5
 ; V1: .loc    1 7 3 is_stmt 1 discriminator 258 # foo.c:7:3
 ; Check that variable __llvm_fs_discriminator__ is generated.
 ; V01: .type   __llvm_fs_discriminator__,@object # @__llvm_fs_discriminator__

llvm/test/CodeGen/X86/fsafdo_test4.ll

@@ -7,8 +7,8 @@
 ; CHECK: .loc    1 0 3 # foo.c:0:3
 ; CHECK: .loc    1 9 5 is_stmt 1 discriminator 2 # foo.c:9:5
 ; CHECK: .loc    1 0 5 is_stmt 0 # :0:5
-; CHECK: .loc    1 9 5 is_stmt 1 discriminator 2 # foo.c:9:5
-; CHECK: .loc    1 0 5 is_stmt 0 # :0:5
+; CHECK: .loc    1 9 5 discriminator 2 # foo.c:9:5
+; CHECK: .loc    1 0 5 # :0:5
 ; CHECK: .loc	   1 7 3 is_stmt 1 discriminator 2 # foo.c:7:3
 ; CHECK: .loc    1 14 3 # foo.c:14:3
 ; Check that variable __llvm_fs_discriminator__ is NOT generated.

llvm/test/CodeGen/X86/pseudo_cmov_lower2.ll

@@ -198,9 +198,6 @@ declare void @llvm.dbg.value(metadata, metadata, metadata)
 ; Like the test for @foo1, but check that the inserted dbg.value does not
 ; affect codegen. The CHECK items below should always be identical to @foo1,
 ; minus the DEBUG_VALUE line and changes in labels..
-; We produce a scope-line source location for the entry block, and then
-; explicitly terminate it in the second block, as there are no other source
-; locations in the function.
 define double @foo1_g(float %p1, double %p2, double %p3) nounwind !dbg !4 {
 ; CHECK-LABEL: foo1_g:
 ; CHECK:       .file   1 "." "test.c"
@@ -211,7 +208,6 @@ define double @foo1_g(float %p1, double %p2, double %p3) nounwind !dbg !4 {
 ; CHECK-NEXT:    movsd {{.*#+}} xmm0 = [1.25E+0,0.0E+0]
 ; CHECK-NEXT:    jae .LBB6_1
 ; CHECK-NEXT:  # %bb.2: # %entry
-; CHECK-NEXT:  .loc    1 0 0 is_stmt 0
 ; CHECK-NEXT:    addsd %xmm2, %xmm0
 ; CHECK-NEXT:    jmp .LBB6_3
 ; CHECK-NEXT:  .LBB6_1:

llvm/test/DebugInfo/MIR/X86/empty-inline.mir

@@ -14,9 +14,7 @@
 # CHECK: Address            Line   Column File   ISA Discriminator OpIndex Flags
 # CHECK-NEXT:                ---
 # CHECK-NEXT:                 25      0      1   0             0         0 is_stmt
-# CHECK-NEXT:                  0      0      1   0             0         0
 # CHECK-NEXT:                 29     28      1   0             0         0 is_stmt prologue_end
-# CHECK-NEXT:                 29     28      1   0             0         0 is_stmt
 # CHECK-NEXT:                 29     28      1   0             0         0 is_stmt end_sequence
 --- |
   source_filename = "t.ll"

llvm/test/DebugInfo/X86/discriminator.ll

@@ -59,4 +59,4 @@ attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "frame-pointer"=
 
 ; CHECK: Address            Line   Column File   ISA Discriminator OpIndex Flags
 ; CHECK: ------------------ ------ ------ ------ --- ------------- ------- -------------
-; CHECK: 0x000000000000000a      2      0      1   0            42       0 is_stmt{{$}}
+; CHECK: 0x000000000000000a      2      0      1   0            42       0 {{$}}

llvm/test/DebugInfo/X86/empty-line-info.ll

@@ -19,9 +19,8 @@ entry:
 }
 
 ;; In a function with no source location, but multiple blocks, there will be
-;; an opening scope-line, but it'll be automagically terminated when we switch
-;; to a new block. Test for this behaviour, and preserve the unconditional
-;; branch by compiling -O0.
+;; an opening scope-line. Test for this behaviour, and preserve the
+;; unconditional branch by compiling -O0.
 
 ; UNOPT-LABEL: bar:
 ; UNOPT-NEXT:   .Lfunc_begin1:
@@ -30,7 +29,6 @@ entry:
 ; UNOPT-NEXT:    movq    %rdi, -8(%rsp)
 ; UNOPT-NEXT:    jmp     .LBB1_1
 ; UNOPT-LABEL: .LBB1_1:
-; UNOPT-NEXT:    .loc    1 0 0 is_stmt 0
 ; UNOPT-NEXT:    movq    -8(%rsp), %rax
 
 define dso_local noundef i32 @bar(ptr nocapture noundef writeonly %baz) local_unnamed_addr !dbg !20 {