[PATCH] D82420: [SimplifyCFG] Drop debug loc in SpeculativelyExecuteBB

[Vedant Kumar via Phabricator via llvm-commits]

vsk created this revision.
vsk added reviewers: aprantl, davide.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.
vsk updated this revision to Diff 272866.
vsk added a comment.

Back out the change for speculated store instructions: a merged location is applied to this instruction.


According to HowToUpdateDebugInfo.rst:

  Preserving the debug locations of speculated instructions can make
  it seem like a condition is true when it's not (or vice versa), which
  leads to a confusing single-stepping experience

This patch follows the recommendation to drop debug locations on
speculated instructions.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D82420

Files:
  llvm/lib/Transforms/Utils/SimplifyCFG.cpp
  llvm/test/Transforms/SimplifyCFG/drop-debug-loc-when-speculating.ll


Index: llvm/test/Transforms/SimplifyCFG/drop-debug-loc-when-speculating.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/SimplifyCFG/drop-debug-loc-when-speculating.ll
@@ -0,0 +1,39 @@
+; RUN: opt -S -o - %s -simplifycfg | FileCheck %s
+
+declare i1 @make_condition()
+
+; CHECK-LABEL: @test1(
+; CHECK: and i1 [[COND:%.*]], [[COND]]{{$}}
+; CHECK: select i1 [[COND]]
+define void @test1() !dbg !6 {
+start:
+  %cond = call i1 @make_condition(), !dbg !8
+  br i1 %cond, label %then, label %else, !dbg !9
+
+then:                                             ; preds = %start
+  %and = and i1 %cond, %cond, !dbg !10
+  br label %else, !dbg !11
+
+else:                                             ; preds = %then, %start
+  %phi = phi i1 [ %cond, %start ], [ %and, %then ], !dbg !12
+  ret void, !dbg !13
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!3, !4}
+!llvm.module.flags = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test.ll", directory: "/")
+!2 = !{}
+!3 = !{i32 6}
+!4 = !{i32 0}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = distinct !DISubprogram(name: "test1", linkageName: "test1", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!7 = !DISubroutineType(types: !2)
+!8 = !DILocation(line: 1, column: 1, scope: !6)
+!9 = !DILocation(line: 2, column: 1, scope: !6)
+!10 = !DILocation(line: 3, column: 2, scope: !6)
+!11 = !DILocation(line: 4, column: 2, scope: !6)
+!12 = !DILocation(line: 5, column: 3, scope: !6)
+!13 = !DILocation(line: 6, column: 3, scope: !6)
Index: llvm/lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2141,9 +2141,14 @@
   }
 
   // Metadata can be dependent on the condition we are hoisting above.
-  // Conservatively strip all metadata on the instruction.
-  for (auto &I : *ThenBB)
+  // Conservatively strip all metadata on the instruction. Drop the debug loc
+  // to avoid making it appear as if the condition is a constant, which would
+  // be misleading while debugging.
+  for (auto &I : *ThenBB) {
+    if (!SpeculatedStoreValue || &I != SpeculatedStore)
+      I.setDebugLoc({});
     I.dropUnknownNonDebugMetadata();
+  }
 
   // Hoist the instructions.
   BB->getInstList().splice(BI->getIterator(), ThenBB->getInstList(),


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D82420.272866.patch
Type: text/x-patch
Size: 2625 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200623/7d6e5cb7/attachment.bin>