From 5b477be72a4eafe4ddd927589b8b4d962d379a3f Mon Sep 17 00:00:00 2001
From: Adrian Prantl <aprantl@apple.com>
Date: Fri, 9 Mar 2018 00:45:04 +0000
Subject: [PATCH] LowerDbgDeclare: ignore dbg.declares for allocas with
 volatile access

There is no point in lowering a dbg.declare describing an alloca that
has volatile loads or stores as users, since the alloca cannot be
elided. Lowering the dbg.declare will result in larger debug info that
may also have worse coverage than just describing the alloca.

rdar://problem/34496278

llvm-svn: 327092
---
 llvm/lib/Transforms/Utils/Local.cpp                | 45 +++++++-----
 llvm/test/DebugInfo/Generic/volatile-alloca.ll     | 83 ++++++++++++++++++++++
 .../Transforms/Util/simplify-dbg-declare-load.ll   |  8 ++-
 3 files changed, 116 insertions(+), 20 deletions(-)
 create mode 100644 llvm/test/DebugInfo/Generic/volatile-alloca.ll

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 1bfa1be..cd96847c 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1322,25 +1322,36 @@ bool llvm::LowerDbgDeclare(Function &F) {
     // stored on the stack, while the dbg.declare can only describe
     // the stack slot (and at a lexical-scope granularity). Later
     // passes will attempt to elide the stack slot.
-    if (AI && !isArray(AI)) {
-      for (auto &AIUse : AI->uses()) {
-        User *U = AIUse.getUser();
-        if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
-          if (AIUse.getOperandNo() == 1)
-            ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
-        } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
-          ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
-        } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
-          // This is a call by-value or some other instruction that
-          // takes a pointer to the variable. Insert a *value*
-          // intrinsic that describes the alloca.
-          DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(),
-                                      DDI->getExpression(), DDI->getDebugLoc(),
-                                      CI);
-        }
+    if (!AI || isArray(AI))
+      continue;
+
+    // A volatile load/store means that the alloca can't be elided anyway.
+    if (llvm::any_of(AI->users(), [](User *U) -> bool {
+          if (LoadInst *LI = dyn_cast<LoadInst>(U))
+            return LI->isVolatile();
+          if (StoreInst *SI = dyn_cast<StoreInst>(U))
+            return SI->isVolatile();
+          return false;
+        }))
+      continue;
+
+    for (auto &AIUse : AI->uses()) {
+      User *U = AIUse.getUser();
+      if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
+        if (AIUse.getOperandNo() == 1)
+          ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
+      } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
+        ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
+      } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
+        // This is a call by-value or some other instruction that
+        // takes a pointer to the variable. Insert a *value*
+        // intrinsic that describes the alloca.
+        DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(),
+                                    DDI->getExpression(), DDI->getDebugLoc(),
+                                    CI);
       }
-      DDI->eraseFromParent();
     }
+    DDI->eraseFromParent();
   }
   return true;
 }
diff --git a/llvm/test/DebugInfo/Generic/volatile-alloca.ll b/llvm/test/DebugInfo/Generic/volatile-alloca.ll
new file mode 100644
index 0000000..438d886
--- /dev/null
+++ b/llvm/test/DebugInfo/Generic/volatile-alloca.ll
@@ -0,0 +1,83 @@
+; RUN: opt -mem2reg -instcombine %s -o - -S | FileCheck %s
+;
+; Test that a dbg.declare describing am alloca with volatile
+; load/stores is not lowered into a dbg.value, since the alloca won't
+; be elided anyway.
+;
+; Generated from:
+;
+; unsigned long long g();
+; void h(unsigned long long);
+; void f() {
+;   volatile unsigned long long v = g();
+;   if (v == 0)
+;     g();
+;   h(v);
+; }
+
+; CHECK: alloca i64
+; CHECK-NOT: call void @llvm.dbg.value
+; CHECK: call void @llvm.dbg.declare
+; CHECK-NOT: call void @llvm.dbg.value
+
+source_filename = "volatile.c"
+
+; Function Attrs: nounwind optsize ssp uwtable
+define void @f() local_unnamed_addr #0 !dbg !8 {
+  %1 = alloca i64, align 8
+  %2 = bitcast i64* %1 to i8*, !dbg !15
+  call void @llvm.lifetime.start.p0i8(i64 8, i8* %2), !dbg !15
+  call void @llvm.dbg.declare(metadata i64* %1, metadata !12, metadata !DIExpression()), !dbg !15
+  %3 = call i64 (...) @g() #4, !dbg !15
+  store volatile i64 %3, i64* %1, align 8, !dbg !15
+  %4 = load volatile i64, i64* %1, align 8, !dbg !15
+  %5 = icmp eq i64 %4, 0, !dbg !15
+  br i1 %5, label %6, label %8, !dbg !15
+
+; <label>:6:                                      ; preds = %0
+  %7 = call i64 (...) @g() #4, !dbg !15
+  br label %8, !dbg !15
+
+; <label>:8:                                      ; preds = %6, %0
+  %9 = load volatile i64, i64* %1, align 8, !dbg !15
+  call void @h(i64 %9) #4, !dbg !15
+  call void @llvm.lifetime.end.p0i8(i64 8, i8* %2), !dbg !15
+  ret void, !dbg !15
+}
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture) #1
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #2
+
+; Function Attrs: optsize
+declare i64 @g(...) local_unnamed_addr #3
+
+; Function Attrs: optsize
+declare void @h(i64) local_unnamed_addr #3
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture) #1
+
+attributes #0 = { nounwind optsize ssp uwtable }
+attributes #1 = { argmemonly nounwind }
+attributes #2 = { nounwind readnone speculatable }
+attributes #3 = { optsize }
+attributes #4 = { optsize }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+!1 = !DIFile(filename: "volatile.c", directory: "/")
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 3, type: !9, isLocal: false, isDefinition: true, scopeLine: 3, isOptimized: true, unit: !0, variables: !11)
+!9 = !DISubroutineType(types: !10)
+!10 = !{null}
+!11 = !{!12}
+!12 = !DILocalVariable(name: "v", scope: !8, file: !1, line: 4, type: !13)
+!13 = !DIDerivedType(tag: DW_TAG_volatile_type, baseType: !14)
+!14 = !DIBasicType(name: "long long unsigned int", size: 64, encoding: DW_ATE_unsigned)
+!15 = !DILocation(line: 4, column: 3, scope: !8)
diff --git a/llvm/test/Transforms/Util/simplify-dbg-declare-load.ll b/llvm/test/Transforms/Util/simplify-dbg-declare-load.ll
index 5aba880..baea744 100644
--- a/llvm/test/Transforms/Util/simplify-dbg-declare-load.ll
+++ b/llvm/test/Transforms/Util/simplify-dbg-declare-load.ll
@@ -13,6 +13,7 @@ declare void @llvm.dbg.value(metadata, metadata, metadata) #0
 define void @julia_fastshortest_6256() #1 {
 top:
   %cp = alloca %foo, align 8
+  %sink = alloca %foo, align 8
   call void @llvm.dbg.declare(metadata %foo* %cp, metadata !1, metadata !16), !dbg !17
   br i1 undef, label %idxend, label %fail
 
@@ -21,9 +22,10 @@ fail:                                             ; preds = %top
 
 idxend:                                           ; preds = %top
 ; CHECK-NOT: call void @llvm.dbg.value(metadata %foo* %cp,
-  %0 = load volatile %foo, %foo* %cp, align 8
-; CHECK: call void @llvm.dbg.value(metadata %foo %0,
-  store volatile %foo %0, %foo* undef, align 8
+  %0 = load %foo, %foo* %cp, align 8
+  store volatile %foo %0, %foo *%sink, align 8
+; CHECK: call void @llvm.dbg.value(metadata %foo %
+  store %foo %0, %foo* undef, align 8
   ret void
 }
 
-- 
2.7.4