[DWARF] Defer creating declaration DIEs until we prepare call site info

It isn't necessary to create DIEs for all of the declaration subprograms
in a CU's retainedTypes list. We can defer creating these subprograms
until we need to prepare a call site tag that refers to one.

This cleanup was mentioned in passing in D70350.

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -924,13 +924,6 @@ DwarfDebug::getOrCreateDwarfCompileUnit(const DICompileUnit *DIUnit) {
     NewCU.setSection(Asm->getObjFileLowering().getDwarfInfoSection());
   }
 
-  // Create DIEs for function declarations used for call site debug info.
-  // Note: Declaration subprograms imported by LTO are not added to the unit's
-  // list of retained types, so their DIEs are not constructed here.
-  for (auto Scope : DIUnit->getRetainedTypes())
-    if (auto *SP = dyn_cast_or_null<DISubprogram>(Scope))
-      NewCU.getOrCreateSubprogramDIE(SP);
-
   CUMap.insert({DIUnit, &NewCU});
   CUDieMap.insert({&NewCU.getUnitDie(), &NewCU});
   return NewCU;

llvm/test/DebugInfo/MIR/AArch64/dbgcall-site-orr-moves.mir

@@ -159,7 +159,7 @@ body:             |
 ...
 
 # CHECK: DW_TAG_GNU_call_site
-# CHECK-NEXT: DW_AT_abstract_origin (0x0000002a "call_int")
+# CHECK-NEXT: DW_AT_abstract_origin ({{.*}} "call_int")
 #
 # CHECK: DW_TAG_GNU_call_site_parameter
 # CHECK-NEXT: DW_AT_location      (DW_OP_reg0 W0)
@@ -205,7 +205,7 @@ body:             |
 ...
 
 # CHECK: DW_TAG_GNU_call_site
-# CHECK-NEXT: DW_AT_abstract_origin (0x0000003e "call_long")
+# CHECK-NEXT: DW_AT_abstract_origin ({{.*}} "call_long")
 #
 # CHECK: DW_TAG_GNU_call_site_parameter
 # CHECK-NEXT: DW_AT_location      (DW_OP_reg0 W0)
@@ -265,7 +265,7 @@ body:             |
 ...
 
 # CHECK: DW_TAG_GNU_call_site
-# CHECK-NEXT: DW_AT_abstract_origin (0x00000052 "call_int_int")
+# CHECK-NEXT: DW_AT_abstract_origin ({{.*}} "call_int_int")
 #
 # CHECK: DW_TAG_GNU_call_site_parameter
 # FIXME: The DW_AT_location attribute should actually refer to W0! See PR44118.

llvm/test/DebugInfo/MIR/X86/debug-call-site-param.mir

@@ -39,17 +39,11 @@
 # CHECK-GNU-NEXT:      DW_AT_location      (DW_OP_reg8 R8)
 # CHECK-GNU-NEXT:      DW_AT_GNU_call_site_value   (DW_OP_breg14 R14+3)
 
-# CHECK-DWARF5: [[getValue_SP:.*]]: DW_TAG_subprogram
-# CHECK-DWARF5-NEXT: DW_AT_name      ("getVal")
-
-# CHECK-DWARF5: [[foo_SP:.*]]: DW_TAG_subprogram
-# CHECK-DWARF5-NEXT: DW_AT_name      ("foo")
-
 # CHECK-DWARF5: DW_TAG_call_site
-# CHECK-DWARF5:   DW_AT_call_origin ([[getValue_SP]])
-#
+# CHECK-DWARF5:   DW_AT_call_origin ([[getValue_SP:.*]])
+
 # CHECK-DWARF5: DW_TAG_call_site
-# CHECK-DWARF5:   DW_AT_call_origin ([[foo_SP]])
+# CHECK-DWARF5:   DW_AT_call_origin ([[foo_SP:.*]])
 # CHECK-DWARF5:   DW_AT_call_return_pc {{.*}}
 # CHECK-DWARF5-EMPTY:
 # CHECK-DWARF5:         DW_TAG_call_site_parameter
@@ -71,6 +65,12 @@
 # CHECK-DWARF5-NEXT:      DW_AT_location      (DW_OP_reg8 R8)
 # CHECK-DWARF5-NEXT:      DW_AT_call_value   (DW_OP_breg14 R14+3)
 
+# CHECK-DWARF5: [[getValue_SP]]: DW_TAG_subprogram
+# CHECK-DWARF5-NEXT: DW_AT_name      ("getVal")
+
+# CHECK-DWARF5: [[foo_SP]]: DW_TAG_subprogram
+# CHECK-DWARF5-NEXT: DW_AT_name      ("foo")
+
 --- |
   ; ModuleID = 'test.c'
   source_filename = "test.c"

llvm/test/DebugInfo/X86/lto-cross-cu-call-origin-ref.ll

@@ -49,10 +49,6 @@
 ; CHECK: DW_TAG_compile_unit
 ; CHECK:   DW_AT_name ("a.c")
 
-; CHECK: DW_TAG_subprogram
-; CHECK:   DW_AT_name ("func_from_b")
-; CHECK:   DW_AT_declaration (true)
-
 ; CHECK: 0x{{0+}}[[NOINLINE_FUNC_IN_A:.*]]: DW_TAG_subprogram
 ; CHECK:   DW_AT_name ("noinline_func_in_a")
 
@@ -81,14 +77,6 @@
 ; CHECK: DW_TAG_compile_unit
 ; CHECK:   DW_AT_name ("b.c")
 
-; CHECK: DW_TAG_subprogram
-; CHECK:   DW_AT_name ("noinline_func_in_a")
-; CHECK:   DW_AT_declaration (true)
-
-; CHECK: DW_TAG_subprogram
-; CHECK:   DW_AT_name ("always_inline_helper_in_a_that_calls_foo")
-; CHECK:   DW_AT_declaration (true)
-
 ; 3) Validate the cross-CU ref from "call_func_in_b_from_a" in a.c.
 ; CHECK: 0x{{0+}}[[FUNC_FROM_B]]: DW_TAG_subprogram
 ; CHECK:   DW_AT_name ("func_from_b")