DebugInfo: Don't lose unreferenced non-trivial by-value parameters

A FastISel optimization was causing us to emit no information for such
parameters & when they go missing we end up emitting a different
function type. By avoiding that shortcut we not only get types correct
(very important) but also location information (handy) - even if it's
only live at the start of a function & may be clobbered later.

Reviewed/discussion by Evan Cheng & Dan Gohman.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184604 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/FastISel.cpp

@@ -97,14 +97,12 @@ bool FastISel::LowerArguments() {
   if (!FastLowerArguments())
     return false;
 
-  // Enter non-dead arguments into ValueMap for uses in non-entry BBs.
+  // Enter arguments into ValueMap for uses in non-entry BBs.
   for (Function::const_arg_iterator I = FuncInfo.Fn->arg_begin(),
          E = FuncInfo.Fn->arg_end(); I != E; ++I) {
-    if (!I->use_empty()) {
+    DenseMap<const Value *, unsigned>::iterator VI = LocalValueMap.find(I);
-      DenseMap<const Value *, unsigned>::iterator VI = LocalValueMap.find(I);
+    assert(VI != LocalValueMap.end() && "Missed an argument?");
-      assert(VI != LocalValueMap.end() && "Missed an argument?");
+    FuncInfo.ValueMap[I] = VI->second;
-      FuncInfo.ValueMap[I] = VI->second;
-    }
   }
   return true;
 }

lib/Target/ARM/ARMFastISel.cpp

@@ -3030,8 +3030,6 @@ bool ARMFastISel::FastLowerArguments() {
   Idx = 0;
   for (Function::const_arg_iterator I = F->arg_begin(), E = F->arg_end();
        I != E; ++I, ++Idx) {
-    if (I->use_empty())
-      continue;
     unsigned SrcReg = GPRArgRegs[Idx];
     unsigned DstReg = FuncInfo.MF->addLiveIn(SrcReg, RC);
     // FIXME: Unfortunately it's necessary to emit a copy from the livein copy.

lib/Target/X86/X86FastISel.cpp

@@ -1732,8 +1732,6 @@ bool X86FastISel::FastLowerArguments() {
   const TargetRegisterClass *RC64 = TLI.getRegClassFor(MVT::i64);
   for (Function::const_arg_iterator I = F->arg_begin(), E = F->arg_end();
        I != E; ++I, ++Idx) {
-    if (I->use_empty())
-      continue;
     bool is32Bit = TLI.getValueType(I->getType()) == MVT::i32;
     const TargetRegisterClass *RC = is32Bit ? RC32 : RC64;
     unsigned SrcReg = is32Bit ? GPR32ArgRegs[Idx] : GPR64ArgRegs[Idx];

test/CodeGen/ARM/fast-isel-call.ll

@@ -92,7 +92,7 @@ declare signext i8 @t7();
 declare zeroext i8 @t8();
 declare zeroext i1 @t9();
 
-define i32 @t10(i32 %argc, i8** nocapture %argv) {
+define i32 @t10() {
 entry:
 ; ARM: @t10
 ; ARM: movw [[R0:l?r[0-9]*]], #0

test/DebugInfo/arguments.ll

@@ -0,0 +1,71 @@
+; REQUIRES: object-emission
+
+; RUN: llc -O0 -filetype=obj < %s > %t
+; RUN: llvm-dwarfdump %t | FileCheck %s
+
+; IR generated from clang -g with the following source:
+; struct foo {
+;   foo(const foo&);
+;   int i;
+; };
+;
+; void func(foo f, foo g) {
+;   f.i++;
+; }
+
+; CHECK: debug_info contents
+; CHECK: DW_TAG_subprogram
+; CHECK-NEXT: DW_AT_MIPS_linkage_name{{.*}}"_Z4func3fooS_"
+; CHECK-NOT: NULL
+; CHECK: DW_TAG_formal_parameter
+; CHECK-NEXT: DW_AT_name{{.*}}"f"
+; CHECK-NOT: NULL
+; CHECK: DW_TAG_formal_parameter
+; CHECK-NEXT: DW_AT_name{{.*}}"g"
+
+%struct.foo = type { i32 }
+
+; Function Attrs: nounwind uwtable
+define void @_Z4func3fooS_(%struct.foo* %f, %struct.foo* %g) #0 {
+entry:
+  call void @llvm.dbg.declare(metadata !{%struct.foo* %f}, metadata !19), !dbg !20
+  call void @llvm.dbg.declare(metadata !{%struct.foo* %g}, metadata !21), !dbg !20
+  %i = getelementptr inbounds %struct.foo* %f, i32 0, i32 0, !dbg !22
+  %0 = load i32* %i, align 4, !dbg !22
+  %inc = add nsw i32 %0, 1, !dbg !22
+  store i32 %inc, i32* %i, align 4, !dbg !22
+  ret void, !dbg !23
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.declare(metadata, metadata) #1
+
+attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"="true" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone }
+
+!llvm.dbg.cu = !{!0}
+
+!0 = metadata !{i32 786449, metadata !1, i32 4, metadata !"clang version 3.4 ", i1 false, metadata !"", i32 0, metadata !2, metadata !2, metadata !3, metadata !2, metadata !2, metadata !""} ; [ DW_TAG_compile_unit ] [/usr/local/google/home/blaikie/dev/scratch/scratch.cpp] [DW_LANG_C_plus_plus]
+!1 = metadata !{metadata !"scratch.cpp", metadata !"/usr/local/google/home/blaikie/dev/scratch"}
+!2 = metadata !{i32 0}
+!3 = metadata !{metadata !4}
+!4 = metadata !{i32 786478, metadata !1, metadata !5, metadata !"func", metadata !"func", metadata !"_Z4func3fooS_", i32 6, metadata !6, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 false, void (%struct.foo*, %struct.foo*)* @_Z4func3fooS_, null, null, metadata !2, i32 6} ; [ DW_TAG_subprogram ] [line 6] [def] [func]
+!5 = metadata !{i32 786473, metadata !1}          ; [ DW_TAG_file_type ] [/usr/local/google/home/blaikie/dev/scratch/scratch.cpp]
+!6 = metadata !{i32 786453, i32 0, i32 0, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !7, i32 0, i32 0} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!7 = metadata !{null, metadata !8, metadata !8}
+!8 = metadata !{i32 786451, metadata !1, null, metadata !"foo", i32 1, i64 32, i64 32, i32 0, i32 0, null, metadata !9, i32 0, null, null} ; [ DW_TAG_structure_type ] [foo] [line 1, size 32, align 32, offset 0] [from ]
+!9 = metadata !{metadata !10, metadata !12}
+!10 = metadata !{i32 786445, metadata !1, metadata !8, metadata !"i", i32 3, i64 32, i64 32, i64 0, i32 0, metadata !11} ; [ DW_TAG_member ] [i] [line 3, size 32, align 32, offset 0] [from int]
+!11 = metadata !{i32 786468, null, null, metadata !"int", i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
+!12 = metadata !{i32 786478, metadata !1, metadata !8, metadata !"foo", metadata !"foo", metadata !"", i32 2, metadata !13, i1 false, i1 false, i32 0, i32 0, null, i32 256, i1 false, null, null, i32 0, metadata !18, i32 2} ; [ DW_TAG_subprogram ] [line 2] [foo]
+!13 = metadata !{i32 786453, i32 0, i32 0, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !14, i32 0, i32 0} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!14 = metadata !{null, metadata !15, metadata !16}
+!15 = metadata !{i32 786447, i32 0, i32 0, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 1088, metadata !8} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [artificial] [from foo]
+!16 = metadata !{i32 786448, null, null, null, i32 0, i64 0, i64 0, i64 0, i32 0, metadata !17} ; [ DW_TAG_reference_type ] [line 0, size 0, align 0, offset 0] [from ]
+!17 = metadata !{i32 786470, null, null, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, metadata !8} ; [ DW_TAG_const_type ] [line 0, size 0, align 0, offset 0] [from foo]
+!18 = metadata !{i32 786468}
+!19 = metadata !{i32 786689, metadata !4, metadata !"f", metadata !5, i32 16777222, metadata !8, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [f] [line 6]
+!20 = metadata !{i32 6, i32 0, metadata !4, null}
+!21 = metadata !{i32 786689, metadata !4, metadata !"g", metadata !5, i32 33554438, metadata !8, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [g] [line 6]
+!22 = metadata !{i32 7, i32 0, metadata !4, null}
+!23 = metadata !{i32 8, i32 0, metadata !4, null} ; [ DW_TAG_imported_declaration ]