Merging r344589:

tstellar · tstellar · commit 4d730d8ff367 · 2018-11-30T17:55:00.000Z
------------------------------------------------------------------------ r344589 | dstenb | 2018-10-16 01:06:48 -0700 (Tue, 16 Oct 2018) | 41 lines [DebugInfo][LCSSA] Rewrite pre-existing debug values outside loop Summary: Extend LCSSA so that debug values outside loops are rewritten to use the PHI nodes that the pass creates. This fixes PR39019. In that case, we ran LCSSA on a loop that was later on vectorized, which left us with something like this: for.cond.cleanup: %add.lcssa = phi i32 [ %add, %for.body ], [ %34, %middle.block ] call void @llvm.dbg.value(metadata i32 %add, ret i32 %add.lcssa for.body: %add = [...] br i1 %exitcond, label %for.cond.cleanup, label %for.body which later resulted in the debug.value becoming undef when removing the scalar loop (and the location would have probably been wrong for the vectorized case otherwise). As we now may need to query the AvailableVals cache more than once for a basic block, FindAvailableVals() in SSAUpdaterImpl is changed so that it updates the cache for blocks that we do not create a PHI node for, regardless of the block's number of predecessors. The debug value in the attached IR reproducer would not be properly rewritten without this. Debug values residing in blocks where we have not inserted any PHI nodes are currently left as-is by this patch. I'm not sure what should be done with those uses. Reviewers: mattd, aprantl, vsk, probinson Reviewed By: mattd, aprantl Subscribers: jmorse, gbedwell, JDevlieghere, llvm-commits Differential Revision: https://reviews.llvm.org/D53130 ------------------------------------------------------------------------ llvm-svn: 348011
diff --git a/llvm/include/llvm/Transforms/Utils/SSAUpdater.h b/llvm/include/llvm/Transforms/Utils/SSAUpdater.h
@@ -76,6 +76,10 @@ class SSAUpdater {
   /// block.
   bool HasValueForBlock(BasicBlock *BB) const;
 
+  /// Return the value for the specified block if the SSAUpdater has one,
+  /// otherwise return nullptr.
+  Value *FindValueForBlock(BasicBlock *BB) const;
+
   /// Construct SSA form, materializing a value that is live at the end
   /// of the specified block.
   Value *GetValueAtEndOfBlock(BasicBlock *BB);
diff --git a/llvm/include/llvm/Transforms/Utils/SSAUpdaterImpl.h b/llvm/include/llvm/Transforms/Utils/SSAUpdaterImpl.h
@@ -357,10 +357,9 @@ class SSAUpdaterImpl {
       BBInfo *Info = *I;
 
       if (Info->DefBB != Info) {
-        // Record the available value at join nodes to speed up subsequent
-        // uses of this SSAUpdater for the same value.
-        if (Info->NumPreds > 1)
-          (*AvailableVals)[Info->BB] = Info->DefBB->AvailableVal;
+        // Record the available value to speed up subsequent uses of this
+        // SSAUpdater for the same value.
+        (*AvailableVals)[Info->BB] = Info->DefBB->AvailableVal;
         continue;
       }
 
diff --git a/llvm/lib/Transforms/Utils/LCSSA.cpp b/llvm/lib/Transforms/Utils/LCSSA.cpp
@@ -41,6 +41,7 @@
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/PredIteratorCache.h"
 #include "llvm/Pass.h"
 #include "llvm/Transforms/Utils.h"
@@ -201,6 +202,21 @@ bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
       SSAUpdate.RewriteUse(*UseToRewrite);
     }
 
+    SmallVector<DbgValueInst *, 4> DbgValues;
+    llvm::findDbgValues(DbgValues, I);
+
+    // Update pre-existing debug value uses that reside outside the loop.
+    auto &Ctx = I->getContext();
+    for (auto DVI : DbgValues) {
+      BasicBlock *UserBB = DVI->getParent();
+      if (InstBB == UserBB || L->contains(UserBB))
+        continue;
+      // We currently only handle debug values residing in blocks where we have
+      // inserted a PHI instruction.
+      if (Value *V = SSAUpdate.FindValueForBlock(UserBB))
+        DVI->setOperand(0, MetadataAsValue::get(Ctx, ValueAsMetadata::get(V)));
+    }
+
     // SSAUpdater might have inserted phi-nodes inside other loops. We'll need
     // to post-process them to keep LCSSA form.
     for (PHINode *InsertedPN : InsertedPHIs) {
diff --git a/llvm/lib/Transforms/Utils/SSAUpdater.cpp b/llvm/lib/Transforms/Utils/SSAUpdater.cpp
@@ -64,6 +64,11 @@ bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
   return getAvailableVals(AV).count(BB);
 }
 
+Value *SSAUpdater::FindValueForBlock(BasicBlock *BB) const {
+  AvailableValsTy::iterator AVI = getAvailableVals(AV).find(BB);
+  return (AVI != getAvailableVals(AV).end()) ? AVI->second : nullptr;
+}
+
 void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
   assert(ProtoType && "Need to initialize SSAUpdater");
   assert(ProtoType == V->getType() &&
diff --git a/llvm/test/Transforms/LCSSA/rewrite-existing-dbg-values.ll b/llvm/test/Transforms/LCSSA/rewrite-existing-dbg-values.ll
@@ -0,0 +1,69 @@
+; RUN: opt -S -lcssa < %s | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Reproducer for PR39019.
+;
+; Verify that the llvm.dbg.value in the %for.cond.cleanup2 block is rewritten
+; to use the PHI node for %add that is created by LCSSA.
+
+; CHECK-LABEL: for.cond.cleanup2:
+; CHECK-NEXT: [[PN:%[^ ]*]] = phi i32 [ %add.lcssa, %for.cond.cleanup1 ]
+; CHECK-NEXT: call void @llvm.dbg.value(metadata i32 [[PN]], metadata [[VAR:![0-9]+]], metadata !DIExpression())
+; CHECK-NEXT: call void @bar(i32 [[PN]])
+
+; CHECK-LABEL: for.body:
+; CHECK: %add = add nsw i32 0, 2
+; CHECK: call void @llvm.dbg.value(metadata i32 %add, metadata [[VAR]], metadata !DIExpression())
+
+; CHECK: [[VAR]] = !DILocalVariable(name: "sum",
+
+; Function Attrs: nounwind
+define void @foo() #0 !dbg !6 {
+entry:
+  br label %for.cond.preheader, !dbg !12
+
+for.cond.preheader:                               ; preds = %for.cond.cleanup1, %entry
+  br label %for.body, !dbg !12
+
+for.cond.cleanup2:                                ; preds = %for.cond.cleanup1
+  call void @llvm.dbg.value(metadata i32 %add, metadata !9, metadata !DIExpression()), !dbg !12
+  tail call void @bar(i32 %add) #0, !dbg !12
+  ret void, !dbg !12
+
+for.cond.cleanup1:                                ; preds = %for.body
+  br i1 false, label %for.cond.preheader, label %for.cond.cleanup2, !dbg !12
+
+for.body:                                         ; preds = %for.body, %for.cond.preheader
+  %add = add nsw i32 0, 2, !dbg !12
+  call void @llvm.dbg.value(metadata i32 %add, metadata !9, metadata !DIExpression()), !dbg !12
+  br i1 false, label %for.body, label %for.cond.cleanup1, !dbg !12
+}
+
+; Function Attrs: nounwind
+declare void @bar(i32) #0
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { nounwind }
+attributes #1 = { nounwind readnone speculatable }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 8.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !2)
+!1 = !DIFile(filename: "foo.c", directory: "/")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 8.0.0"}
+!6 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 10, type: !7, isLocal: false, isDefinition: true, scopeLine: 10, isOptimized: true, unit: !0, retainedNodes: !8)
+!7 = !DISubroutineType(types: !2)
+!8 = !{!9}
+!9 = !DILocalVariable(name: "sum", scope: !10, file: !1, line: 11, type: !11)
+!10 = !DILexicalBlockFile(scope: !6, file: !1, discriminator: 0)
+!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!12 = !DILocation(line: 0, scope: !10)
