[DWARF] Missing location debug information with -O2.

Check that Machine CSE correctly handles during the transformation, the
debug location information for local variables.

Differential Revision: https://reviews.llvm.org/D50887

llvm-svn: 341025

llvm/include/llvm/CodeGen/MachineInstr.h

@@ -1530,6 +1530,9 @@ public:
   /// Add all implicit def and use operands to this instruction.
   void addImplicitDefUseOperands(MachineFunction &MF);
 
+  /// Scan instructions following MI and collect any matching DBG_VALUEs.
+  void collectDebugValues(SmallVectorImpl<MachineInstr *> &DbgValues);
+
 private:
   /// If this instruction is embedded into a MachineFunction, return the
   /// MachineRegisterInfo object for the current function, otherwise

llvm/lib/CodeGen/MachineCSE.cpp

@@ -180,6 +180,14 @@ bool MachineCSE::PerformTrivialCopyPropagation(MachineInstr *MI,
       continue;
     LLVM_DEBUG(dbgs() << "Coalescing: " << *DefMI);
     LLVM_DEBUG(dbgs() << "***     to: " << *MI);
+
+    // Collect matching debug values.
+    SmallVector<MachineInstr *, 2> DbgValues;
+    DefMI->collectDebugValues(DbgValues);
+    // Propagate SrcReg to debug value instructions.
+    for (auto *DBI : DbgValues)
+      DBI->getOperand(0).setReg(SrcReg);
+
     // Propagate SrcReg of copies to MI.
     MO.setReg(SrcReg);
     MRI->clearKillFlags(SrcReg);

llvm/lib/CodeGen/MachineInstr.cpp

@@ -2031,3 +2031,20 @@ void llvm::updateDbgValueForSpill(MachineInstr &Orig, int FrameIndex) {
   Orig.getOperand(1).ChangeToImmediate(0U);
   Orig.getOperand(3).setMetadata(Expr);
 }
+
+void MachineInstr::collectDebugValues(
+                                SmallVectorImpl<MachineInstr *> &DbgValues) {
+  MachineInstr &MI = *this;
+  if (!MI.getOperand(0).isReg())
+    return;
+
+  MachineBasicBlock::iterator DI = MI; ++DI;
+  for (MachineBasicBlock::iterator DE = MI.getParent()->end();
+       DI != DE; ++DI) {
+    if (!DI->isDebugValue())
+      return;
+    if (DI->getOperand(0).isReg() &&
+        DI->getOperand(0).getReg() == MI.getOperand(0).getReg())
+      DbgValues.push_back(&*DI);
+  }
+}

llvm/lib/CodeGen/MachineSink.cpp

@@ -513,25 +513,6 @@ bool MachineSinking::PostponeSplitCriticalEdge(MachineInstr &MI,
   return true;
 }
 
-/// collectDebgValues - Scan instructions following MI and collect any
-/// matching DBG_VALUEs.
-static void collectDebugValues(MachineInstr &MI,
-                               SmallVectorImpl<MachineInstr *> &DbgValues) {
-  DbgValues.clear();
-  if (!MI.getOperand(0).isReg())
-    return;
-
-  MachineBasicBlock::iterator DI = MI; ++DI;
-  for (MachineBasicBlock::iterator DE = MI.getParent()->end();
-       DI != DE; ++DI) {
-    if (!DI->isDebugValue())
-      return;
-    if (DI->getOperand(0).isReg() &&
-        DI->getOperand(0).getReg() == MI.getOperand(0).getReg())
-      DbgValues.push_back(&*DI);
-  }
-}
-
 /// isProfitableToSinkTo - Return true if it is profitable to sink MI.
 bool MachineSinking::isProfitableToSinkTo(unsigned Reg, MachineInstr &MI,
                                           MachineBasicBlock *MBB,
@@ -758,7 +739,7 @@ static void performSink(MachineInstr &MI, MachineBasicBlock &SuccToSinkTo,
                         MachineBasicBlock::iterator InsertPos) {
   // Collect matching debug values.
   SmallVector<MachineInstr *, 2> DbgValuesToSink;
-  collectDebugValues(MI, DbgValuesToSink);
+  MI.collectDebugValues(DbgValuesToSink);
 
   // If we cannot find a location to use (merge with), then we erase the debug
   // location to prevent debug-info driven tools from potentially reporting

llvm/test/CodeGen/X86/debuginfo-locations-dce.ll

@@ -0,0 +1,72 @@
+; RUN: llc -O2 %s -o %t -filetype=obj
+; RUN: llvm-dwarfdump -debug-info %t | FileCheck %s
+
+; Check that Machine CSE correctly handles during the transformation, the
+; debug location information for variables.
+
+; Generated with clang -c -g -O2
+
+; typedef float __attribute__((__vector_size__(16))) f4;
+; f4 get();
+; int main() {
+;   float MyVar = get()[0];
+;   if (MyVar)
+;     return 1;
+; }
+
+; ModuleID = 'test.cpp'
+source_filename = "test.cpp"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-linux-gnu"
+
+define dso_local i32 @main() !dbg !7 {
+entry:
+  %call = tail call <4 x float> @_Z3getv(), !dbg !14
+  %vecext = extractelement <4 x float> %call, i32 0, !dbg !14
+  call void @llvm.dbg.value(metadata float %vecext, metadata !12, metadata !DIExpression()), !dbg !15
+  %tobool = fcmp une float %vecext, 0.000000e+00, !dbg !16
+  %. = zext i1 %tobool to i32, !dbg !18
+  ret i32 %., !dbg !19
+}
+
+declare dso_local <4 x float> @_Z3getv()
+
+declare void @llvm.dbg.value(metadata, metadata, metadata) #2
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 8.0.0 (trunk 339665)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test.cpp", directory: ".")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 8.0.0 (trunk 339665)"}
+!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 3, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "MyVar", scope: !7, file: !1, line: 4, type: !13)
+!13 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
+!14 = !DILocation(line: 4, column: 18, scope: !7)
+!15 = !DILocation(line: 4, column: 9, scope: !7)
+!16 = !DILocation(line: 5, column: 7, scope: !17)
+!17 = distinct !DILexicalBlock(scope: !7, file: !1, line: 5, column: 7)
+!18 = !DILocation(line: 6, column: 5, scope: !17)
+!19 = !DILocation(line: 7, column: 1, scope: !7)
+
+; Look at the debug location information for variable 'MyVar'.
+; Verify that we see a sequence of DI entries, that looks like:
+; DW_TAG_variable
+;   DW_AT_location        (0x00000000
+;     [0x0000000000000009,  0x0000000000000012): DW_OP_reg17 XMM0)
+;   DW_AT_name    ("MyVar")
+
+; CHECK-LABEL: DW_TAG_variable
+; CHECK-NEXT: DW_AT_location{{.*}}
+; CHECK-NEXT: {{.*}}DW_OP_reg17 XMM0
+; CHECK-NEXT: DW_AT_name{{.*}}("MyVar")
+