[DebugInfo][LoopVectorize] Preserve DL in induction PHI and Add

[gramanas]

Summary

Continuation of D48769.

In this case the induction phi and add instructions created
in the vector part of the loop were missing DL.

The i8-induction.ll also fails debugify even after this patch:

opt -S -enable-debugify -loop-vectorize i8-induction.ll -disable-output
ERROR: Instruction with empty DebugLoc in function f --  %index = phi i32 [ 0, %vector.ph ], [ %index.next, %vector.body ]
ERROR: Instruction with empty DebugLoc in function f --  %vec.phi = phi <4 x i8> [ <i8 0, i8 1, i8 1, i8 1>, %vector.ph ], [ %5, %vector.body ]
ERROR: Instruction with empty DebugLoc in function f --  %index.next = add i32 %index, 4
ERROR: Instruction with empty DebugLoc in function f --  %9 = icmp eq i32 %index.next, 16
ERROR: Instruction with empty DebugLoc in function f --  br i1 %9, label %middle.block, label %vector.body, !llvm.loop !32
ERROR: Instruction with empty DebugLoc in function f --  %cmp.n = icmp eq i32 16, 16
ERROR: Instruction with empty DebugLoc in function f --  %bc.merge.rdx = phi i8 [ 0, %scalar.ph ], [ %10, %middle.block ]
ERROR: Instruction with empty DebugLoc in function f --  %mul.lcssa = phi i8 [ %mul, %for.body ], [ %10, %middle.block ]
CheckModuleDebugify: FAIL

but those are from different parts of the code so they will be dealt with in
another patch.

[gramanas]

typo in test

[vsk]

lib/Transforms/Vectorize/LoopVectorize.cpp

1824

Why is the debug location of the entry value the correct location to use for an induction variable phi? I'd expect a merged location to be applied to the phi, based on its incoming values.

test/Transforms/LoopVectorize/i8-induction.ll

15

A reader might not expect to see a DILocation here. Please move this to the end of the file. That's where the metadata would appear in an IR dump.

15

Please add a comment explaining why the number '5' is here.

[gramanas]

Make test more readable

[gramanas]

lib/Transforms/Vectorize/LoopVectorize.cpp

1824

I figured that since this Phi is basically the for loop we are optimizing (in the test case below)
%vec.ind = phi <4 x i8> [ undef, %vector.ph ], [ %vec.ind.next, %vector.body ]
it should get the same DL as the add instruction later.

Also the entry val as mentioned in InnerLoopVectorizer::widenIntOrFpInduction (that calls the function I edited) is
// The value from the original loop to which we are mapping the new induction variable.
that I believe holds the correct DL.

OTOH, I could merge this DL with the vector preHeader BB's terminating instruction that results in this phi. Would this be a better approach?
Basically I could add setDebugLoc(DILocation::getMergedLocation(EntryVal->getDL(), Br->getDL()) after the Phi's incoming values are added, at the end of the function.

test/Transforms/LoopVectorize/i8-induction.ll

15

I wanted to make sure that it's not an artificial DL. I made it explicit that it's not line: 0 now.

[vsk]

lib/Transforms/Vectorize/LoopVectorize.cpp

1824

Thanks for the explanation. Using EntryVal's location makes sense to me now.

test/Transforms/LoopVectorize/i8-induction.ll

15

I thought it was better to use line: 5, because it makes it clear that the location comes from "%c.015 = phi i8". A comment would help explain that to readers.

[gramanas]

Use exact line in test

[vsk]

Thanks, LGTM.

lib/Transforms/Vectorize/LoopVectorize.cpp

Value *SplatVF = isa<Constant>(Mul)
                        ? ConstantVector::getSplat(VF, cast<Constant>(Mul))
                        : Builder.CreateVectorSplat(VF, Mul);
   Builder.restoreIP(CurrIP);
 
   // We may need to add the step a number of times, depending on the unroll
   // factor. The last of those goes into the PHI.
   PHINode *VecInd = PHINode::Create(SteppedStart->getType(), 2, "vec.ind",
                                     &*LoopVectorBody->getFirstInsertionPt());
+  VecInd->setDebugLoc(EntryVal->getDebugLoc());
   Instruction *LastInduction = VecInd;
   for (unsigned Part = 0; Part < UF; ++Part) {
     VectorLoopValueMap.setVectorValue(EntryVal, Part, LastInduction);
 
     if (isa<TruncInst>(EntryVal))
       addMetadata(LastInduction, EntryVal);
     recordVectorLoopValueForInductionCast(II, EntryVal, LastInduction, Part);
 
     LastInduction = cast<Instruction>(addFastMathFlag(
         Builder.CreateBinOp(AddOp, LastInduction, SplatVF, "step.add")));
+    LastInduction->setDebugLoc(EntryVal->getDebugLoc());
   }
 
   // Move the last step to the end of the latch block. This ensures consistent
   // placement of all induction updates.
   auto *LoopVectorLatch = LI->getLoopFor(LoopVectorBody)->getLoopLatch();
   auto *Br = cast<BranchInst>(LoopVectorLatch->getTerminator());
   auto *ICmp = cast<Instruction>(Br->getCondition());
   LastInduction->moveBefore(ICmp);

test/Transforms/LoopVectorize/i8-induction.ll

 ; RUN: opt < %s  -loop-vectorize -force-vector-interleave=1 -force-vector-width=4 -dce -instcombine -S
+; RUN: opt < %s -debugify -loop-vectorize -S | FileCheck %s --check-prefix=DEBUGLOC
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 
 @a = common global i8 0, align 1
 @b = common global i8 0, align 1
 
 define void @f() nounwind uwtable ssp {
+; Check that the induction phis and adds have debug location
+; DEBUGLOC-LABEL vector.body:
+; DEBUGLOC:        %vec.ind = phi {{.*}}, !dbg ![[DbgLoc:[0-9]+]]
+; DEBUGLOC:        %vec.ind.next = add {{.*}}, !dbg ![[DbgLoc]]
+;
+; DEBUGLOC:        ![[DbgLoc]] = !DILocation(line: 5
 scalar.ph:
   store i8 0, i8* inttoptr (i64 1 to i8*), align 1
   %0 = load i8, i8* @a, align 1
   br label %for.body
 
 for.body:
   %mul16 = phi i8 [ 0, %scalar.ph ], [ %mul, %for.body ]              ; <------- i8 induction var.
   %c.015 = phi i8 [ undef, %scalar.ph ], [ %conv8, %for.body ]