[DAGCombiner] Fix SDLoc in a (sext (sextload x)) combine (3/N)

[vsk]

Summary

Prior to this patch, for the given test case, we would apply the
location associated with the sdiv instruction to instructions which
perform the load.

Part of: llvm.org/PR37262

[aprantl]

That looks obviously correct. Thanks!

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

SDValue DAGCombiner::visitSIGN_EXTEND(SDNode *N) {
   // fold (sext (sextload x)) -> (sext (truncate (sextload x)))
   // fold (sext ( extload x)) -> (sext (truncate (sextload x)))
   if ((ISD::isSEXTLoad(N0.getNode()) || ISD::isEXTLoad(N0.getNode())) &&
       ISD::isUNINDEXEDLoad(N0.getNode()) && N0.hasOneUse()) {
     LoadSDNode *LN0 = cast<LoadSDNode>(N0);
     EVT MemVT = LN0->getMemoryVT();
     if ((!LegalOperations && !LN0->isVolatile()) ||
         TLI.isLoadExtLegal(ISD::SEXTLOAD, VT, MemVT)) {
-      SDValue ExtLoad = DAG.getExtLoad(ISD::SEXTLOAD, DL, VT, LN0->getChain(),
-                                       LN0->getBasePtr(), MemVT,
-                                       LN0->getMemOperand());
+      SDValue ExtLoad =
+          DAG.getExtLoad(ISD::SEXTLOAD, SDLoc(LN0), VT, LN0->getChain(),
+                         LN0->getBasePtr(), MemVT, LN0->getMemOperand());
       CombineTo(N, ExtLoad);
       DAG.ReplaceAllUsesOfValueWith(SDValue(LN0, 1), ExtLoad.getValue(1));
       return SDValue(N, 0);   // Return N so it doesn't get rechecked!
     }
   }
 
   // fold (sext (and/or/xor (load x), cst)) ->
   //      (and/or/xor (sextload x), (sext cst))

test/CodeGen/ARM/fold-sext-sextload.ll

+; RUN: llc -mtriple armv7 %s -stop-before=livedebugvalues -o - | FileCheck %s
+
+define <4 x i8> @i(<4 x i8>*) !dbg !8 {
+  %2 = load <4 x i8>, <4 x i8>* %0, align 4, !dbg !14
+  ; CHECK: $[[reg:.*]] = VLD1LNd32 {{.*}} debug-location !14 :: (load 4 from %ir.0)
+  ; CHECK-NEXT: VMOVLsv8i16 {{.*}} $[[reg]], {{.*}} debug-location !14
+  ; CHECK-NEXT: VMOVLsv4i32 {{.*}} $[[reg]], {{.*}} debug-location !14
+
+  %3 = sdiv <4 x i8> zeroinitializer, %2, !dbg !15
+  call void @llvm.dbg.value(metadata <4 x i8> %2, metadata !11, metadata !DIExpression()), !dbg !14
+  call void @llvm.dbg.value(metadata <4 x i8> %3, metadata !13, metadata !DIExpression()), !dbg !15
+  ret <4 x i8> %3, !dbg !16
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.debugify = !{!0, !1, !2, !3}
+!llvm.module.flags = !{!4}
+!llvm.dbg.cu = !{!5}
+
+!0 = !{i32 24}
+!1 = !{i32 19}
+!2 = !{i32 3}
+!3 = !{i32 2}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = distinct !DICompileUnit(language: DW_LANG_C, file: !6, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !7)
+!6 = !DIFile(filename: "/Users/vsk/Desktop/test.ll", directory: "/")
+!7 = !{}
+!8 = distinct !DISubprogram(name: "i", linkageName: "i", scope: null, file: !6, line: 1, type: !9, isLocal: false, isDefinition: true, scopeLine: 1, isOptimized: true, unit: !5, variables: !10)
+!9 = !DISubroutineType(types: !7)
+!10 = !{!11, !13}
+!11 = !DILocalVariable(name: "1", scope: !8, file: !6, line: 1, type: !12)
+!12 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
+!13 = !DILocalVariable(name: "2", scope: !8, file: !6, line: 2, type: !12)
+!14 = !DILocation(line: 1, column: 1, scope: !8)
+!15 = !DILocation(line: 2, column: 1, scope: !8)
+!16 = !DILocation(line: 3, column: 1, scope: !8)
+!17 = !{i32 2, !"Debug Info Version", i32 3}