[SROA] Preserve DebugLoc when rewriting alloca partitions

[gramanas]

Summary

When rewriting an alloca partition copy the DL from the
old alloca over the the new one.

Based on Greg's report
https://bugs.llvm.org/show_bug.cgi?id=37942

[probinson]

Is there an existing test for rewriting the alloca, that you could modify? Instead of adding a whole new test file.
Otherwise seems pretty straightforward. This appears to be a common problem, failing to setDebugLoc after creating a new instruction.

[vsk]

In D48640#1144941, @probinson wrote:

Is there an existing test for rewriting the alloca, that you could modify? Instead of adding a whole new test file.
Otherwise seems pretty straightforward. This appears to be a common problem, failing to setDebugLoc after creating a new instruction.

+ 1 on all points.

lib/Transforms/Scalar/SROA.cpp

4032 ↗

(On Diff #153055)

Please end sentences in comments with periods.

[gramanas]

Addressing the comments

[vsk]

test/Transforms/SROA/alignment.ll

2 ↗

(On Diff #153117)

It's OK for a change to instcombine to break the test you're adding here, e.g by disabling a combine.

Is there a test you can repurpose which doesn't rely on instcombine to hit the code path you've changed?

[gramanas]

Remove -instcombine from the RUN clause of the test.

[gramanas]

test/Transforms/SROA/alignment.ll

2 ↗

(On Diff #153117)

Yes, you are absolutely right. For some reason I thought I it was the combination of the two that caused the -check-debugify error.

There are some more tests that without this patch fail to preserve the DL. Should I add DEBUGLOC tests there as well or is one enough?

[vsk]

LGTM, thanks!

llvm/trunk/lib/Transforms/Scalar/SROA.cpp

if (SliceTy == AI.getAllocatedType() && P.beginOffset() == 0) {
     Alignment = MinAlign(Alignment, P.beginOffset());
     // If we will get at least this much alignment from the type alone, leave
     // the alloca's alignment unconstrained.
     if (Alignment <= DL.getABITypeAlignment(SliceTy))
       Alignment = 0;
     NewAI = new AllocaInst(
       SliceTy, AI.getType()->getAddressSpace(), nullptr, Alignment,
         AI.getName() + ".sroa." + Twine(P.begin() - AS.begin()), &AI);
+    // Copy the old AI debug location over to the new one.
+    NewAI->setDebugLoc(AI.getDebugLoc());
     ++NumNewAllocas;
   }
 
   LLVM_DEBUG(dbgs() << "Rewriting alloca partition "
                     << "[" << P.beginOffset() << "," << P.endOffset()
                     << ") to: " << *NewAI << "\n");
 
   // Track the high watermark on the worklist as it is only relevant for

llvm/trunk/test/Transforms/SROA/alignment.ll

 ; RUN: opt < %s -sroa -S | FileCheck %s
+; RUN: opt -debugify -sroa -S < %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-i64:32:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-n8:16:32:64"
 
 declare void @llvm.memcpy.p0i8.p0i8.i32(i8*, i8*, i32, i1)
 
 define void @test1({ i8, i8 }* %a, { i8, i8 }* %b) {
 ; CHECK-LABEL: @test1(
 ; CHECK: %[[gep_a0:.*]] = getelementptr inbounds { i8, i8 }, { i8, i8 }* %a, i64 0, i32 0
 ; CHECK: %[[a0:.*]] = load i8, i8* %[[gep_a0]], align 16

 
 define void @test2() {
 ; CHECK-LABEL: @test2(
 ; CHECK: alloca i16
 ; CHECK: load i8, i8* %{{.*}}
 ; CHECK: store i8 42, i8* %{{.*}}
 ; CHECK: ret void
 
+; Check that when sroa rewrites the alloca partition
+; it preserves the original DebugLocation.
+; DEBUGLOC-LABEL: @test2(
+; DEBUGLOC: {{.*}} = alloca {{.*}} !dbg ![[DbgLoc:[0-9]+]]
+;
+; DEBUGLOC: ![[DbgLoc]] = !DILocation(
+
 entry:
   %a = alloca { i8, i8, i8, i8 }, align 2
   %gep1 = getelementptr { i8, i8, i8, i8 }, { i8, i8, i8, i8 }* %a, i32 0, i32 1
   %cast1 = bitcast i8* %gep1 to i16*
   store volatile i16 0, i16* %cast1
   %gep2 = getelementptr { i8, i8, i8, i8 }, { i8, i8, i8, i8 }* %a, i32 0, i32 2
   %result = load i8, i8* %gep2
   store i8 42, i8* %gep2