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[DWARF] Null out the debug locs of load instructions that have been moved by GVN

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performing partial redundancy elimination (PRE). Not doing so can cause jumpy line
tables and confusing (though correct) source attributions.

Differential Revision: https://reviews.llvm.org/D27857

llvm-svn: 291037
This commit is contained in:
Wolfgang Pieb 2017-01-04 23:58:26 +00:00
parent 8ae77dbc0f
commit 74f59cd854
2 changed files with 18 additions and 9 deletions
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14
lib/Transforms/Scalar/GVN.cpp
View File

@ -1572,6 +1572,13 @@ bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock,
// Assign value numbers to the new instructions.
for (Instruction *I : NewInsts) {
// Instructions that have been inserted in predecessor(s) to materialize
// the load address do not retain their original debug locations. Doing
// so could lead to confusing (but correct) source attributions.
// FIXME: How do we retain source locations without causing poor debugging
// behavior?
I->setDebugLoc(DebugLoc());
// FIXME: We really _ought_ to insert these value numbers into their
// parent's availability map. However, in doing so, we risk getting into
// ordering issues. If a block hasn't been processed yet, we would be
@ -1601,8 +1608,11 @@ bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock,
if (auto *RangeMD = LI->getMetadata(LLVMContext::MD_range))
NewLoad->setMetadata(LLVMContext::MD_range, RangeMD);
// Transfer DebugLoc.
NewLoad->setDebugLoc(LI->getDebugLoc());
// We do not propagate the old load's debug location, because the new
// load now lives in a different BB, and we want to avoid a jumpy line
// table.
// FIXME: How do we retain source locations without causing poor debugging
// behavior?
// Add the newly created load.
ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred,

13
test/Transforms/GVN/PRE/phi-translate.ll
View File

@ -4,18 +4,17 @@ target datalayout = "e-p:64:64:64"
; CHECK-LABEL: @foo(
; CHECK: entry.end_crit_edge:
; CHECK: %j.phi.trans.insert = sext i32 %x to i64, !dbg [[J_LOC:![0-9]+]]
; CHECK: %q.phi.trans.insert = getelementptr {{.*}}, !dbg [[Q_LOC:![0-9]+]]
; CHECK: %n.pre = load i32, i32* %q.phi.trans.insert, !dbg [[N_LOC:![0-9]+]]
; CHECK: %[[INDEX:[a-z0-9.]+]] = sext i32 %x to i64{{$}}
; CHECK: %[[ADDRESS:[a-z0-9.]+]] = getelementptr [100 x i32], [100 x i32]* @G, i64 0, i64 %[[INDEX]]{{$}}
; CHECK: %n.pre = load i32, i32* %[[ADDRESS]]{{$}}
; CHECK: br label %end
; CHECK: then:
; CHECK: store i32 %z
; CHECK: end:
; CHECK: %n = phi i32 [ %n.pre, %entry.end_crit_edge ], [ %z, %then ], !dbg [[N_LOC]]
; CHECK: %n = phi i32 [ %n.pre, %entry.end_crit_edge ], [ %z, %then ], !dbg [[N_LOC:![0-9]+]]
; CHECK: ret i32 %n
; CHECK-DAG: [[J_LOC]] = !DILocation(line: 45, column: 1, scope: !{{.*}})
; CHECK-DAG: [[Q_LOC]] = !DILocation(line: 46, column: 1, scope: !{{.*}})
; CHECK-DAG: [[N_LOC]] = !DILocation(line: 47, column: 1, scope: !{{.*}})
; CHECK: [[N_LOC]] = !DILocation(line: 47, column: 1, scope: !{{.*}})
@G = external global [100 x i32]
define i32 @foo(i32 %x, i32 %z) !dbg !6 {