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[Util] Refer to [s|z]exts of args when converting dbg.declares (fix PR35400)

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When converting dbg.declares, if the described value is a [s|z]ext,
refer to the ext directly instead of referring to its operand.

This fixes a narrowing bug (the debugger got the sign of a variable
wrong, see llvm.org/PR35400).

The main reason to refer to the ext's operand was that an optimization
may remove the ext itself, leading to a dropped variable. Now that
InstCombine has been taught to use replaceAllDbgUsesWith (r336451), this
is less of a concern. Other passes can/should adopt this API as needed
to fix dropped variable bugs.

Differential Revision: https://reviews.llvm.org/D51813

llvm-svn: 349214
This commit is contained in:
Vedant Kumar 2018-12-15 00:03:33 +00:00
parent 51ebca085c
commit 2153f9e846
2 changed files with 9 additions and 32 deletions
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27
lib/Transforms/Utils/Local.cpp
View File

@ -1297,33 +1297,6 @@ void llvm::ConvertDebugDeclareToDebugValue(DbgVariableIntrinsic *DII,
return;
}
// 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) {
// If this DII 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 = DII->getModule()->getDataLayout();
Ops.push_back(DL.getTypeSizeInBits(ExtendedArg->getType()));
DIExpr = Builder.createExpression(Ops);
}
DV = ExtendedArg;
}
if (!LdStHasDebugValue(DIVar, DIExpr, SI))
Builder.insertDbgValueIntrinsic(DV, DIVar, DIExpr, DII->getDebugLoc(),
SI);

14
test/Transforms/Util/split-bit-piece.ll → test/Transforms/Util/dbg-user-of-aext.ll
View File

@ -1,6 +1,6 @@
; 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.
; (here exposed through the SROA) pass refers to [s|z]exts of values (as
; opposed to the operand of a [s|z]ext).
; RUN: opt -S -sroa %s | FileCheck %s
; Built from:
@ -21,8 +21,8 @@
; CHECK: call void @llvm.dbg.value(metadata i8 %g.coerce0, metadata ![[VAR_STRUCT:[0-9]+]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 8))
; CHECK: call void @llvm.dbg.value(metadata i64 %g.coerce1, metadata ![[VAR_STRUCT]], metadata !DIExpression(DW_OP_LLVM_fragment, 32, 64))
; CHECK: call void @llvm.dbg.value(metadata i1 %b, metadata ![[VAR_BOOL:[0-9]+]], metadata !DIExpression())
; CHECK: call void @llvm.dbg.value(metadata i1 %frag, metadata ![[VAR_FRAG:[0-9]+]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 1))
; CHECK: call void @llvm.dbg.value(metadata i8 %frombool, metadata ![[VAR_BOOL:[0-9]+]], metadata !DIExpression())
; CHECK: call void @llvm.dbg.value(metadata i8 %frombool1, metadata ![[VAR_FRAG:[0-9]+]], metadata !DIExpression(DW_OP_LLVM_fragment, 0, 4))
%struct.foo = type { i8, i64 }
@ -40,13 +40,17 @@ entry:
%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
%frombool1 = sext 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
}
; CHECK: ![[VAR_STRUCT]] = !DILocalVariable(name: "g"
; CHECK: ![[VAR_BOOL]] = !DILocalVariable(name: "b"
; CHECK: ![[VAR_FRAG]] = !DILocalVariable(name: "frag"
; Function Attrs: nounwind readnone speculatable
declare void @llvm.dbg.declare(metadata, metadata, metadata) #1