<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Apr 28, 2015 at 4:01 PM, Adrian Prantl <span dir="ltr"><<a href="mailto:aprantl@apple.com" target="_blank">aprantl@apple.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">Author: adrian<br>
Date: Tue Apr 28 18:01:24 2015<br>
New Revision: 236059<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=236059&view=rev" target="_blank">http://llvm.org/viewvc/llvm-project?rev=236059&view=rev</a><br>
Log:<br>
Debug Info: Represent local anonymous unions as anonymous unions<br>
in the debug info. This patch deletes a hack that emits the members<br>
of local anonymous unions as local variables.<br>
<br>
Besides being morally wrong, the existing representation using local<br>
variables breaks internal assumptions about the local variables' storage<br>
size.<br>
<br>
Compiling<br>
<br>
```<br>
void fn1() {<br>
union {<br>
int i;<br>
char c;<br>
};<br>
i = c;<br>
}<br>
<br>
```<br>
<br>
with -g -O3 -verify will cause the verifier to fail after SROA splits<br>
the 32-bit storage for the "local variable" c into two pieces because the<br>
second piece is clearly outside the 8-bit range that is expected for a<br>
variable of type char. Given the choice I'd rather fix the debug<br>
representation than weaken the verifier.<br>
<br>
Debuggers generally already know how to deal with anonymous unions when<br>
they are members of C++ record types, but they may have problems finding<br>
the local anonymous struct members in the expression evaluator.<br></blockquote><div><br>Seems we're not so lucky: <a href="http://lab.llvm.org:8011/builders/clang-x86_64-ubuntu-gdb-75/builds/21650/steps/gdb-75-check/logs/gdb.cp__anon-union.exp">http://lab.llvm.org:8011/builders/clang-x86_64-ubuntu-gdb-75/builds/21650/steps/gdb-75-check/logs/gdb.cp__anon-union.exp</a><br><br>Could you revert & I'll look into getting you a reduced test case/demonstration of the issue? (can you run GDB 7.5? Perhaps a simple test case would demonstrate the issue if you're lucky, otherwise I can reduce one from the failing test case)<br> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<br>
rdar://problem/20730771<br>
<br>
Modified:<br>
cfe/trunk/lib/CodeGen/CGDebugInfo.cpp<br>
cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp<br>
<br>
Modified: cfe/trunk/lib/CodeGen/CGDebugInfo.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGDebugInfo.cpp?rev=236059&r1=236058&r2=236059&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGDebugInfo.cpp?rev=236059&r1=236058&r2=236059&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/lib/CodeGen/CGDebugInfo.cpp (original)<br>
+++ cfe/trunk/lib/CodeGen/CGDebugInfo.cpp Tue Apr 28 18:01:24 2015<br>
@@ -2835,31 +2835,6 @@ void CGDebugInfo::EmitDeclare(const VarD<br>
return;<br>
} else if (isa<VariableArrayType>(VD->getType()))<br>
Expr.push_back(llvm::dwarf::DW_OP_deref);<br>
- } else if (const RecordType *RT = dyn_cast<RecordType>(VD->getType())) {<br>
- // If VD is an anonymous union then Storage represents value for<br>
- // all union fields.<br>
- const RecordDecl *RD = cast<RecordDecl>(RT->getDecl());<br>
- if (RD->isUnion() && RD->isAnonymousStructOrUnion()) {<br>
- for (const auto *Field : RD->fields()) {<br>
- llvm::MDType *FieldTy = getOrCreateType(Field->getType(), Unit);<br>
- StringRef FieldName = Field->getName();<br>
-<br>
- // Ignore unnamed fields. Do not ignore unnamed records.<br>
- if (FieldName.empty() && !isa<RecordType>(Field->getType()))<br>
- continue;<br>
-<br>
- // Use VarDecl's Tag, Scope and Line number.<br>
- auto *D = DBuilder.createLocalVariable(<br>
- Tag, Scope, FieldName, Unit, Line, FieldTy,<br>
- CGM.getLangOpts().Optimize, Flags, ArgNo);<br>
-<br>
- // Insert an llvm.dbg.declare into the current block.<br>
- DBuilder.insertDeclare(Storage, D, DBuilder.createExpression(Expr),<br>
- llvm::DebugLoc::get(Line, Column, Scope),<br>
- Builder.GetInsertBlock());<br>
- }<br>
- return;<br>
- }<br>
}<br>
<br>
// Create the descriptor for the variable.<br>
<br>
Modified: cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp?rev=236059&r1=236058&r2=236059&view=diff" target="_blank">http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp?rev=236059&r1=236058&r2=236059&view=diff</a><br>
==============================================================================<br>
--- cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp (original)<br>
+++ cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp Tue Apr 28 18:01:24 2015<br>
@@ -21,8 +21,26 @@ int test_it() {<br>
return (c == 1);<br>
}<br>
<br>
+// This is not necessary (and actually harmful because it breaks IR assumptions)<br>
+// for local variables.<br>
+void foo() {<br>
+ union {<br>
+ int i;<br>
+ char c;<br>
+ };<br>
+ i = 8;<br>
+}<br>
+<br>
// CHECK: [[FILE:.*]] = !MDFile(filename: "{{.*}}debug-info-anon-union-vars.cpp",<br>
// CHECK: !MDGlobalVariable(name: "c",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true<br>
// CHECK: !MDGlobalVariable(name: "d",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true<br>
// CHECK: !MDGlobalVariable(name: "a",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true<br>
// CHECK: !MDGlobalVariable(name: "b",{{.*}} file: [[FILE]], line: 6,{{.*}} isLocal: true, isDefinition: true<br>
+// CHECK: !MDLocalVariable(<br>
+// CHECK-NOT: name:<br>
+// CHECK: type: ![[UNION:[0-9]+]]<br>
+// CHECK: ![[UNION]] = !MDCompositeType(tag: DW_TAG_union_type,<br>
+// CHECK-NOT: name:<br>
+// CHECK: elements<br>
+// CHECK: !MDDerivedType(tag: DW_TAG_member, name: "i", scope: ![[UNION]],<br>
+// CHECK: !MDDerivedType(tag: DW_TAG_member, name: "c", scope: ![[UNION]],<br>
<br>
<br>
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</blockquote></div><br></div></div>