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

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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

llvm-svn: 348753
This commit is contained in:
Jeremy Morse 2018-12-10 12:04:08 +00:00
parent 1bf1a156d6
commit a06b163d5c
3 changed files with 8 additions and 7 deletions
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3
llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
View File

@ -749,6 +749,9 @@ InstrEmitter::EmitDbgValue(SDDbgValue *SD,
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.

3
llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
View File

@ -5312,7 +5312,8 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
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;

9
llvm/test/DebugInfo/X86/sdag-dangling-dbgvalue.ll
View File

@ -63,9 +63,9 @@ target triple = "x86_64-apple-macosx10.4.0"
@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()