[llvm] r348753 - [DebugInfo] Don't drop dbg.value's of nullptr

[Jeremy Morse via llvm-commits]

Author: jmorse
Date: Mon Dec 10 04:04:08 2018
New Revision: 348753

URL: http://llvm.org/viewvc/llvm-project?rev=348753&view=rev
Log:
[DebugInfo] Don't drop dbg.value's of nullptr

Currently, dbg.value's of "nullptr" are dropped when entering a SelectionDAG --
apparently just because of an oversight when recognising Values that are
constant (see PR39787). This patch adds ConstantPointerNull to the list of
constants that can be turned into DBG_VALUEs.

The matter of what bit-value a null pointer constant in LLVM has was raised
in this mailing list thread:

  http://lists.llvm.org/pipermail/llvm-dev/2018-December/128234.html

Where it transpires LLVM relies on (IR) null pointers being zero valued,
thus I've baked this assumption into the patch.

Differential Revision: https://reviews.llvm.org/D55227

Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
    llvm/trunk/test/DebugInfo/X86/sdag-dangling-dbgvalue.ll

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/InstrEmitter.cpp?rev=348753&r1=348752&r2=348753&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/InstrEmitter.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/InstrEmitter.cpp Mon Dec 10 04:04:08 2018
@@ -749,6 +749,9 @@ InstrEmitter::EmitDbgValue(SDDbgValue *S
         MIB.addImm(CI->getSExtValue());
     } else if (const ConstantFP *CF = dyn_cast<ConstantFP>(V)) {
       MIB.addFPImm(CF);
+    } else if (isa<ConstantPointerNull>(V)) {
+      // Note: This assumes that all nullptr constants are zero-valued.
+      MIB.addImm(0);
     } else {
       // Could be an Undef.  In any case insert an Undef so we can see what we
       // dropped.

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp?rev=348753&r1=348752&r2=348753&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp Mon Dec 10 04:04:08 2018
@@ -5312,7 +5312,8 @@ SelectionDAGBuilder::visitIntrinsicCall(
       return nullptr;
 
     SDDbgValue *SDV;
-    if (isa<ConstantInt>(V) || isa<ConstantFP>(V) || isa<UndefValue>(V)) {
+    if (isa<ConstantInt>(V) || isa<ConstantFP>(V) || isa<UndefValue>(V) ||
+        isa<ConstantPointerNull>(V)) {
       SDV = DAG.getConstantDbgValue(Variable, Expression, V, dl, SDNodeOrder);
       DAG.AddDbgValue(SDV, nullptr, false);
       return nullptr;

Modified: llvm/trunk/test/DebugInfo/X86/sdag-dangling-dbgvalue.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/DebugInfo/X86/sdag-dangling-dbgvalue.ll?rev=348753&r1=348752&r2=348753&view=diff
==============================================================================
--- llvm/trunk/test/DebugInfo/X86/sdag-dangling-dbgvalue.ll (original)
+++ llvm/trunk/test/DebugInfo/X86/sdag-dangling-dbgvalue.ll Mon Dec 10 04:04:08 2018
@@ -63,9 +63,9 @@ target triple = "x86_64-apple-macosx10.4
 @S = global %struct.SS { i32 23, i32 -17 }, align 4, !dbg !0
 
 ; Verify that the def comes before the for foo1.
-; TODO: Currently dbg.value for bar1 is dropped(?), is that expected?
 define i32 @test1() local_unnamed_addr #0 !dbg !17 {
 ; CHECK-LABEL: bb.0.entry1
+; CHECK-NEXT:    DBG_VALUE 0, $noreg, ![[BAR1]], !DIExpression()
 ; CHECK-NEXT:    [[REG1:%[0-9]+]]:gr64 =
 ; CHECK-NEXT:    DBG_VALUE [[REG1]], $noreg, ![[FOO1]], !DIExpression()
 entry1:
@@ -99,11 +99,9 @@ entry3:
 }
 
 ; Verify that the def comes before the for bar4.
-; TODO: Currently dbg.value for foo4 is dropped. It is set to null and not
-;       used. Just like in test1 it can be discussed if there should be a
-;       DBG_VALUE for foo4 here.
 define i32 @test4() local_unnamed_addr #0 !dbg !40 {
 ; CHECK-LABEL: bb.0.entry4
+; CHECK-NEXT:    DBG_VALUE 0, $noreg, ![[FOO4]], !DIExpression()
 ; CHECK-NEXT:    [[REG4:%[0-9]+]]:gr64 =
 ; CHECK-NEXT:    DBG_VALUE [[REG4]], $noreg, ![[BAR4]], !DIExpression()
 entry4:
@@ -114,10 +112,9 @@ entry4:
 }
 
 ; Verify that we do not get a DBG_VALUE that maps foo5 to @S here.
-; TODO: foo5 is set to null, and it is not really used. Just like in test1 it
-;       can be discussed if there should be a DBG_VALUE for foo5 here.
 define i32 @test5() local_unnamed_addr #0 !dbg !47 {
 ; CHECK-LABEL: bb.0.entry5:
+; CHECK-NEXT:    DBG_VALUE 0, $noreg, ![[FOO5]], !DIExpression()
 ; CHECK-NEXT:    [[REG5:%[0-9]+]]:gr64 =
 ; CHECK-NEXT:    DBG_VALUE [[REG5]], $noreg, ![[BAR5]], !DIExpression()
 ; CHECK-NOT:     DBG_VALUE [[REG5]], $noreg, ![[FOO5]], !DIExpression()