[PATCH] D19564: Update Debug Intrinsics in RewriteUsesOfClonedInstructions in LoopRotation
Thomas Jablin via llvm-commits
llvm-commits at lists.llvm.org
Wed Apr 27 12:46:36 PDT 2016
The short answer is, "Yes."
If a DbgInfoIntrinsic extended the live range of Value before LoopRotation,
then LoopRotation may create a situation where the definition of the Value
no dominates the DbgInfoIntrinsic. If so, the proposed patch will insert a
PHINode.
If DbgInfoIntrinsics can extend the live range of a Value, then register
allocation and other aspects of optimization and code generation will
inevitably change. The alternative is pruning DbgInfoIntrinsics if they use
Values that no longer dominate them and when they would extend the
live-range of a Value.
If the DbgInfoIntrinsic is inside the live-range of a Value and does not
extend it, no additional PHINodes will be need to be inserted.
On Wed, Apr 27, 2016 at 1:27 PM, David Blaikie <dblaikie at gmail.com> wrote:
> Does this cause changes in non-debug IR in the presence of debug info
> intrinsics? (you mention that "If there were uses of values produced by
> these instructions that were outside the loop, we have to insert PHI nodes
> to merge the two values." - that sounds like it could be a problem, as
> enabling debug info is not intended to change optimization/code generation)
>
> On Tue, Apr 26, 2016 at 3:34 PM, Thomas Jablin via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> tjablin created this revision.
>> tjablin added reviewers: kbarton, hfinkel, cycheng.
>> tjablin added a subscriber: llvm-commits.
>> Herald added a subscriber: mzolotukhin.
>>
>> Loop rotation clones instruction from the old header into the preheader.
>> If there were uses of values produced by these instructions that were
>> outside the loop, we have to insert PHI nodes to merge the two values. If
>> the values are used by DbgIntrinsics they will be used as a MetadataAsValue
>> of a ValueAsMetadata of the original values, and iterating all of the uses
>> of the original value will not update the DbgIntrinsics. The new code
>> checks if the values are used by DbgIntrinsics and if so, updates them
>> using essentially the same logic as the original code.
>>
>> The attached testcase demonstrates the issue. Without the fix, the
>> DbgIntrinic outside the loop uses values computed inside the loop, even
>> though these values do not dominate the DbgIntrinsic.
>>
>> http://reviews.llvm.org/D19564
>>
>> Files:
>> lib/Transforms/Scalar/LoopRotation.cpp
>> test/Transforms/LoopRotate/dbgvalue.ll
>>
>> Index: test/Transforms/LoopRotate/dbgvalue.ll
>> ===================================================================
>> --- test/Transforms/LoopRotate/dbgvalue.ll
>> +++ test/Transforms/LoopRotate/dbgvalue.ll
>> @@ -7,6 +7,7 @@
>> ; CHECK-LABEL: define i32 @tak(
>> ; CHECK: entry
>> ; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 %x
>> +; CHECK: tail call void @llvm.dbg.value(metadata i32 %call
>>
>> entry:
>> br label %tailrecurse
>> @@ -37,6 +38,44 @@
>> ret i32 %z.tr, !dbg !17
>> }
>>
>> +define i32 @tak2(i32 %x, i32 %y, i32 %z) nounwind ssp !dbg !0 {
>> +; CHECK-LABEL: define i32 @tak2(
>> +; CHECK: entry
>> +; CHECK: tail call void @llvm.dbg.value(metadata i32 %x.tr
>> +; CHECK: tail call void @llvm.dbg.value(metadata i32 %x.tr
>> +
>> +entry:
>> + br label %tailrecurse
>> +
>> +tailrecurse: ; preds = %if.then,
>> %entry
>> + %x.tr = phi i32 [ %x, %entry ], [ %call, %if.then ]
>> + %y.tr = phi i32 [ %y, %entry ], [ %call9, %if.then ]
>> + %z.tr = phi i32 [ %z, %entry ], [ %call14, %if.then ]
>> + %cmp = icmp slt i32 %y.tr, %x.tr, !dbg !12
>> + br i1 %cmp, label %if.then, label %if.end, !dbg !12
>> +
>> +if.then: ; preds = %tailrecurse
>> + tail call void @llvm.dbg.value(metadata i32 %x.tr, i64 0, metadata
>> !6, metadata !DIExpression()), !dbg !7
>> + tail call void @llvm.dbg.value(metadata i32 %y.tr, i64 0, metadata
>> !8, metadata !DIExpression()), !dbg !9
>> + tail call void @llvm.dbg.value(metadata i32 %z.tr, i64 0, metadata
>> !10, metadata !DIExpression()), !dbg !11
>> + %sub = sub nsw i32 %x.tr, 1, !dbg !14
>> + %call = tail call i32 @tak(i32 %sub, i32 %y.tr, i32 %z.tr), !dbg !14
>> + %sub6 = sub nsw i32 %y.tr, 1, !dbg !14
>> + %call9 = tail call i32 @tak(i32 %sub6, i32 %z.tr, i32 %x.tr), !dbg !14
>> + %sub11 = sub nsw i32 %z.tr, 1, !dbg !14
>> + %call14 = tail call i32 @tak(i32 %sub11, i32 %x.tr, i32 %y.tr), !dbg
>> !14
>> + br label %tailrecurse
>> +
>> +if.end: ; preds = %tailrecurse
>> + tail call void @llvm.dbg.value(metadata i32 %x.tr, i64 0, metadata
>> !6, metadata !DIExpression()), !dbg !7
>> + tail call void @llvm.dbg.value(metadata i32 %y.tr, i64 0, metadata
>> !8, metadata !DIExpression()), !dbg !9
>> + tail call void @llvm.dbg.value(metadata i32 %z.tr, i64 0, metadata
>> !10, metadata !DIExpression()), !dbg !11
>> + br label %return, !dbg !16
>> +
>> +return: ; preds = %if.end
>> + ret i32 %z.tr, !dbg !17
>> +}
>> +
>> @channelColumns = external global i64
>> @horzPlane = external global i8*, align 8
>>
>> Index: lib/Transforms/Scalar/LoopRotation.cpp
>> ===================================================================
>> --- lib/Transforms/Scalar/LoopRotation.cpp
>> +++ lib/Transforms/Scalar/LoopRotation.cpp
>> @@ -108,6 +108,33 @@
>>
>> // Anything else can be handled by SSAUpdater.
>> SSA.RewriteUse(U);
>> +
>> + // Replace MetadataAsValue(ValueAsMetadata(OrigHeaderVal)) uses in
>> debug
>> + // intrinsics
>> + LLVMContext &C = OrigHeader->getContext();
>> + if (ValueAsMetadata *VAM =
>> ValueAsMetadata::getIfExists(OrigHeaderVal)) {
>> + if (MetadataAsValue *MAV = MetadataAsValue::getIfExists(C, VAM))
>> {
>> + for (auto UI = MAV->use_begin(), E = MAV->use_end(); UI != E;
>> ) {
>> + // Grab the use before incrementing the iterator.
>> + Use &U = *UI++;
>> + DbgInfoIntrinsic *UserInst =
>> cast<DbgInfoIntrinsic>(U.getUser());
>> + BasicBlock *UserBB = UserInst->getParent();
>> +
>> + // The original users in the OrigHeader are already using the
>> + // original definitions.
>> + if (UserBB == OrigHeader)
>> + continue;
>> +
>> + // Users in the OrigPreHeader need to use the value to which
>> the
>> + // original definitions are mapped and anything else can be
>> handled
>> + // by the SSAUpdater
>> + Value *NewVal = UserBB == OrigPreheader ?
>> + OrigPreHeaderVal :
>> + SSA.GetValueInMiddleOfBlock(UserBB);
>> + U = MetadataAsValue::get(C, ValueAsMetadata::get(NewVal));
>> + }
>> + }
>> + }
>> }
>> }
>> }
>>
>>
>>
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>>
>>
>
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