[PATCH] D47097: [DebugInfo] Preserve scope in auto generated StoreInst

Vedant Kumar via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Wed May 23 10:40:03 PDT 2018

vsk added inline comments.

Comment at: lib/CodeGen/CGExpr.cpp:72
+  // Set debug location in order to preserve the scope
+  Alloca->setDebugLoc(Builder.getCurrentDebugLocation());
   if (AllocaAddr)
I think we need to be a bit more careful here. The current debug location stored in the builder may not be an artificial 0-location. This may cause non-linear single-stepping behavior. Consider this example:

void foo() {
  if (...) {
    int var = ...; //< Clang emits an alloca for "var".

The current debug location at the line "int var = ..." would be at line 4. But the alloca is emitted in the entry block of the function. In the debugger, this may result in strange single-stepping behavior when stepping into foo(). You could step to line 4, then line 2, then line 3, then line 4 again.

I think we can avoid that by setting an artificial location on allocas.

Comment at: lib/CodeGen/CGExpr.cpp:105
   return new llvm::AllocaInst(Ty, CGM.getDataLayout().getAllocaAddrSpace(),
                               ArraySize, Name, AllocaInsertPt);
Why not apply the location here to cover more cases?

Comment at: test/CodeGen/debug-info-preserve-scope.c:11
+// CHECK: [[B:%.*]] = alloca i32 {{.*}} !dbg ![[artificialDbgLoc:[0-9]+]]
+// CHECK: store i32 {{.*}} !dbg ![[artificialDbgLoc]]
Why is "B" captured?

  rC Clang


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