PR32288: Describe a bool parameter's DWARF location with a simple register

[dblaikie]

Summary

There's no need (& a bit incorrect) to mask off the high bits of the
register reference when describing a simple bool value.

[aprantl]

Took me a while to find the functional change amidst the refactoring :-)
As discussed in the PR, this LGTM, thanks!
One inline comment about a comment.

lib/Transforms/Utils/Local.cpp

1118 ↗

(On Diff #92087)

Does this comment still match our understanding?
Particularly the The fragment we're describing will always be smaller than the variable size bit.

llvm/trunk/lib/Transforms/Utils/Local.cpp

static bool PhiHasDebugValue(DILocalVariable *DIVar,
   return false;
 }
 
 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
 /// that has an associated llvm.dbg.decl intrinsic.
 void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
                                            StoreInst *SI, DIBuilder &Builder) {
   auto *DIVar = DDI->getVariable();
-  auto *DIExpr = DDI->getExpression();
   assert(DIVar && "Missing variable");
+  auto *DIExpr = DDI->getExpression();
+  Value *DV = SI->getOperand(0);
 
   // If an argument is zero extended then use argument directly. The ZExt
   // may be zapped by an optimization pass in future.
   Argument *ExtendedArg = nullptr;
   if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
     ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
   if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
     ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
   if (ExtendedArg) {
-    // We're now only describing a subset of the variable. The fragment we're
-    // describing will always be smaller than the variable size, because
-    // VariableSize == Size of Alloca described by DDI. Since SI stores
-    // to the alloca described by DDI, if it's first operand is an extend,
-    // we're guaranteed that before extension, the value was narrower than
-    // the size of the alloca, hence the size of the described variable.
-    SmallVector<uint64_t, 3> Ops;
-    unsigned FragmentOffset = 0;
-    // If this already is a bit fragment, we drop the bit fragment from the
-    // expression and record the offset.
-    auto Fragment = DIExpr->getFragmentInfo();
-    if (Fragment) {
-      Ops.append(DIExpr->elements_begin(), DIExpr->elements_end()-3);
-      FragmentOffset = Fragment->OffsetInBits;
-    } else {
-      Ops.append(DIExpr->elements_begin(), DIExpr->elements_end());
-    }
+    // If this DDI was already describing only a fragment of a variable, ensure
+    // that fragment is appropriately narrowed here.
+    // But if a fragment wasn't used, describe the value as the original
+    // argument (rather than the zext or sext) so that it remains described even
+    // if the sext/zext is optimized away. This widens the variable description,
+    // leaving it up to the consumer to know how the smaller value may be
+    // represented in a larger register.
+    if (auto Fragment = DIExpr->getFragmentInfo()) {
+      unsigned FragmentOffset = Fragment->OffsetInBits;
+      SmallVector<uint64_t, 3> Ops(DIExpr->elements_begin(),
+                                   DIExpr->elements_end() - 3);
       Ops.push_back(dwarf::DW_OP_LLVM_fragment);
       Ops.push_back(FragmentOffset);
       const DataLayout &DL = DDI->getModule()->getDataLayout();
       Ops.push_back(DL.getTypeSizeInBits(ExtendedArg->getType()));
-    auto NewDIExpr = Builder.createExpression(Ops);
-    if (!LdStHasDebugValue(DIVar, NewDIExpr, SI))
-      Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, NewDIExpr,
-                                      DDI->getDebugLoc(), SI);
-  } else if (!LdStHasDebugValue(DIVar, DIExpr, SI))
-    Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, DIExpr,
-                                    DDI->getDebugLoc(), SI);
+      DIExpr = Builder.createExpression(Ops);
+    }
+    DV = ExtendedArg;
+  }
+  if (!LdStHasDebugValue(DIVar, DIExpr, SI))
+    Builder.insertDbgValueIntrinsic(DV, 0, DIVar, DIExpr, DDI->getDebugLoc(),
+                                    SI);
 }
 
 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
 /// that has an associated llvm.dbg.decl intrinsic.
 void llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
                                            LoadInst *LI, DIBuilder &Builder) {
   auto *DIVar = DDI->getVariable();
   auto *DIExpr = DDI->getExpression();

llvm/trunk/test/Transforms/Util/split-bit-piece.ll

 ; Checks that llvm.dbg.declare -> llvm.dbg.value conversion utility
 ; (here exposed through the SROA) pass, properly inserts bit_piece expressions
 ; if it only describes part of the variable.
 ; RUN: opt -S -sroa %s | FileCheck %s
 
-; Function Attrs: nounwind readnone
-declare void @llvm.dbg.declare(metadata, metadata, metadata) #0
+; Built from:
+; struct foo { bool b; long i; };
+; void f(bool b, bool expr, foo g) {
+; }
+; And modifying the frag dbg.declare to use a fragmented DIExpression (with offset: 0, size: 4)
+; to test the dbg.declare+fragment case here.
 
-; Function Attrs: nounwind uwtable
-define hidden void @_ZN6__tsan9FastState14SetHistorySizeEi(i32 %hs) #1 align 2 {
+; Expect two fragments:
+; * first starting at bit 0, 8 bits (for the bool)
+; * second starting at bit 32, 32 bits (for the long)
+; (this happens to create/demonstrate a gap from bits [7, 32))
+
+; But also check that a complex expression is not used for a lone bool
+; parameter. It can reference the register it's in directly without masking off
+; high bits or anything
+
+; CHECK: call void @llvm.dbg.value(metadata i8 %g.coerce0, i64 0, metadata ![[VAR_STRUCT:[0-9]+]], metadata ![[EXPR_STRUCT1:[0-9]+]])
+; CHECK: call void @llvm.dbg.value(metadata i64 %g.coerce1, i64 0, metadata ![[VAR_STRUCT]], metadata ![[EXPR_STRUCT2:[0-9]+]])
+; CHECK: call void @llvm.dbg.value(metadata i1 %b, i64 0, metadata ![[VAR_BOOL:[0-9]+]], metadata ![[EXPR_BOOL:[0-9]+]])
+; CHECK: call void @llvm.dbg.value(metadata i1 %frag, i64 0, metadata ![[FRAG_BOOL:[0-9]+]], metadata ![[FRAG_BOOL:[0-9]+]])
+; CHECK: ![[EXPR_STRUCT1]] = !DIExpression(DW_OP_LLVM_fragment, 0, 8)
+; CHECK: ![[EXPR_STRUCT2]] = !DIExpression(DW_OP_LLVM_fragment, 32, 64)
+; CHECK: ![[EXPR_BOOL]] = !DIExpression()
+; CHECK: ![[FRAG_BOOL]] = !DIExpression(DW_OP_LLVM_fragment, 0, 1)
+
+%struct.foo = type { i8, i64 }
+
+; Function Attrs: noinline nounwind uwtable
+define void @_Z1fbb3foo(i1 zeroext %b, i1 zeroext %frag, i8 %g.coerce0, i64 %g.coerce1) #0 !dbg !6 {
 entry:
-  %hs.addr = alloca i32, align 4
-  %v1 = alloca i64, align 8
-  %v2 = alloca i64, align 8
-  store i32 %hs, i32* %hs.addr, align 4
-; CHECK: call void @llvm.dbg.value(metadata i32 %hs, i64 0, metadata !{{[0-9]+}}, metadata ![[EXPR:[0-9]+]])
-; CHECK: ![[EXPR]] = !DIExpression(DW_OP_LLVM_fragment, 0
-  call void @llvm.dbg.declare(metadata i64* %v1, metadata !9, metadata !12), !dbg !13
-  %0 = load i32, i32* %hs.addr, align 4
-  %conv = sext i32 %0 to i64
-  store i64 %conv, i64* %v1, align 8
-  %1 = load i64, i64* %v2, align 8
-  unreachable
+  %g = alloca %struct.foo, align 8
+  %b.addr = alloca i8, align 1
+  %frag.addr = alloca i8, align 1
+  %0 = bitcast %struct.foo* %g to { i8, i64 }*
+  %1 = getelementptr inbounds { i8, i64 }, { i8, i64 }* %0, i32 0, i32 0
+  store i8 %g.coerce0, i8* %1, align 8
+  %2 = getelementptr inbounds { i8, i64 }, { i8, i64 }* %0, i32 0, i32 1
+  store i64 %g.coerce1, i64* %2, align 8
+  %frombool = zext i1 %b to i8
+  store i8 %frombool, i8* %b.addr, align 1
+  call void @llvm.dbg.declare(metadata i8* %b.addr, metadata !15, metadata !16), !dbg !17
+  %frombool1 = zext i1 %frag to i8
+  store i8 %frombool1, i8* %frag.addr, align 1
+  call void @llvm.dbg.declare(metadata i8* %frag.addr, metadata !18, metadata !23), !dbg !19
+  call void @llvm.dbg.declare(metadata %struct.foo* %g, metadata !20, metadata !16), !dbg !21
+  ret void, !dbg !22
 }
 
-attributes #0 = { nounwind readnone }
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+attributes #0 = { noinline nounwind uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone speculatable }
 
 !llvm.dbg.cu = !{!0}
-!llvm.module.flags = !{!7}
-!llvm.ident = !{!8}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
 
-!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 3.8.0 (trunk 256979) (llvm/trunk 257107)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, retainedTypes: !2)
-!1 = !DIFile(filename: "tsan_shadow_test.cc", directory: "/tmp")
-!2 = !{!3, !5}
-!3 = !DICompositeType(tag: DW_TAG_class_type, name: "FastState", file: !4, line: 91, size: 64, align: 64, identifier: "_ZTSN6__tsan9FastStateE")
-!4 = !DIFile(filename: "/mnt/extra/llvm/projects/compiler-rt/lib/tsan/rtl/tsan_rtl.h", directory: "/tmp")
-!5 = distinct !DIDerivedType(tag: DW_TAG_typedef, name: "u64", line: 78, baseType: !6)
-!6 = !DIBasicType(name: "long long unsigned int", size: 64, align: 64, encoding: DW_ATE_unsigned)
-!7 = !{i32 2, !"Debug Info Version", i32 3}
-!8 = !{!"clang version 3.8.0 (trunk 256979) (llvm/trunk 257107)"}
-!9 = !DILocalVariable(name: "v1", scope: !10, file: !4, line: 136, type: !5)
-!10 = distinct !DILexicalBlock(scope: !11, file: !4, line: 136, column: 5)
-!11 = distinct !DISubprogram(name: "SetHistorySize", linkageName: "_ZN6__tsan9FastState14SetHistorySizeEi", scope: !3, file: !4, line: 135, isLocal: false, isDefinition: true, scopeLine: 135, flags: DIFlagPrototyped, isOptimized: false, unit: !0)
-!12 = !DIExpression()
-!13 = !DILocation(line: 136, column: 5, scope: !10)
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 5.0.0 (trunk 303077) (llvm/trunk 303098)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "foo.cpp", directory: "/usr/local/google/home/blaikie/dev/scratch")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 5.0.0 (trunk 303077) (llvm/trunk 303098)"}
+!6 = distinct !DISubprogram(name: "f", linkageName: "_Z1fbb3foo", scope: !1, file: !1, line: 2, type: !7, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!7 = !DISubroutineType(types: !8)
+!8 = !{null, !9, !9, !10}
+!9 = !DIBasicType(name: "bool", size: 8, encoding: DW_ATE_boolean)
+!10 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "foo", file: !1, line: 1, size: 128, elements: !11, identifier: "_ZTS3foo")
+!11 = !{!12, !13}
+!12 = !DIDerivedType(tag: DW_TAG_member, name: "b", scope: !10, file: !1, line: 1, baseType: !9, size: 8)
+!13 = !DIDerivedType(tag: DW_TAG_member, name: "i", scope: !10, file: !1, line: 1, baseType: !14, size: 64, offset: 64)
+!14 = !DIBasicType(name: "long int", size: 64, encoding: DW_ATE_signed)
+!15 = !DILocalVariable(name: "b", arg: 1, scope: !6, file: !1, line: 2, type: !9)
+!16 = !DIExpression()
+!17 = !DILocation(line: 2, column: 13, scope: !6)
+!18 = !DILocalVariable(name: "frag", arg: 2, scope: !6, file: !1, line: 2, type: !9)
+!19 = !DILocation(line: 2, column: 21, scope: !6)
+!20 = !DILocalVariable(name: "g", arg: 3, scope: !6, file: !1, line: 2, type: !10)
+!21 = !DILocation(line: 2, column: 31, scope: !6)
+!22 = !DILocation(line: 3, column: 1, scope: !6)
+!23 = !DIExpression(DW_OP_LLVM_fragment, 0, 4)