Strip metadata when speculatively hoisting instructions

This is fix for PR24059.

When we are hoisting instruction above some condition it may turn out
that metadata on this instruction was control dependant on the condition.
This metadata becomes invalid and we need to drop it.

This patch should cover most obvious places of speculative execution (which
I have found by greping isSafeToSpeculativelyExecute). I think there are more
cases but at least this change covers the severe ones.

Differential Revision: http://reviews.llvm.org/D14398

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252604 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/LoopInfo.cpp b/lib/Analysis/LoopInfo.cpp
index 9ee7236..e679b7a 100644 (file)
--- a/lib/Analysis/LoopInfo.cpp
+++ b/lib/Analysis/LoopInfo.cpp
@@ -120,6 +120,13 @@ bool Loop::makeLoopInvariant(Instruction *I, bool &Changed,
 
   // Hoist.
   I->moveBefore(InsertPt);
+
+  // There is possibility of hoisting this instruction above some arbitrary
+  // condition. Any metadata defined on it can be control dependent on this
+  // condition. Conservatively strip it here so that we don't give any wrong
+  // information to the optimizer.
+  I->dropUnknownNonDebugMetadata();
+
   Changed = true;
   return true;
 }

diff --git a/lib/Transforms/Scalar/LICM.cpp b/lib/Transforms/Scalar/LICM.cpp
index ba39afd..6d70cdc 100644 (file)
--- a/lib/Transforms/Scalar/LICM.cpp
+++ b/lib/Transforms/Scalar/LICM.cpp
@@ -672,6 +672,10 @@ static bool hoist(Instruction &I, BasicBlock *Preheader) {
   // Move the new node to the Preheader, before its terminator.
   I.moveBefore(Preheader->getTerminator());
 
+  // Metadata can be dependent on the condition we are hoisting above.
+  // Conservatively strip all metadata on the instruction.
+  I.dropUnknownNonDebugMetadata();
+
   if (isa<LoadInst>(I)) ++NumMovedLoads;
   else if (isa<CallInst>(I)) ++NumMovedCalls;
   ++NumHoisted;

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index e0c598f..ff81e7d 100644 (file)
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -1618,6 +1618,11 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
     SpeculatedStore->setOperand(0, S);
   }
 
+  // Metadata can be dependent on the condition we are hoisting above.
+  // Conservatively strip all metadata on the instruction.
+  for (auto &I: *ThenBB)
+    I.dropUnknownNonDebugMetadata();
+
   // Hoist the instructions.
   BB->getInstList().splice(BI->getIterator(), ThenBB->getInstList(),
                            ThenBB->begin(), std::prev(ThenBB->end()));

diff --git a/test/Analysis/TypeBasedAliasAnalysis/licm.ll b/test/Analysis/TypeBasedAliasAnalysis/licm.ll
index fe07730..d2aee58 100644 (file)
--- a/test/Analysis/TypeBasedAliasAnalysis/licm.ll
+++ b/test/Analysis/TypeBasedAliasAnalysis/licm.ll
@@ -5,7 +5,7 @@
 
 ; CHECK: @foo
 ; CHECK:      entry:
-; CHECK-NEXT:   %tmp3 = load double*, double** @P, !tbaa !0
+; CHECK-NEXT:   %tmp3 = load double*, double** @P
 ; CHECK-NEXT:   br label %for.body
 
 @P = common global double* null

diff --git a/test/Transforms/LICM/hoist-deref-load.ll b/test/Transforms/LICM/hoist-deref-load.ll
index c384a85..fd10c5d 100644 (file)
--- a/test/Transforms/LICM/hoist-deref-load.ll
+++ b/test/Transforms/LICM/hoist-deref-load.ll
@@ -388,5 +388,49 @@ for.end:                                          ; preds = %for.inc, %entry
   ret void
 }
 
+; In this test we should be able to only hoist load from %cptr. We can't hoist
+; load from %c because it's dereferenceability can depend on %cmp1 condition.
+; By moving it out of the loop we break this dependency and can not rely
+; on the dereferenceability anymore.
+; In other words this test checks that we strip dereferenceability  metadata
+; after hoisting an instruction.
+
+; CHECK-LABEL: @test10
+; CHECK: %c = load i32*, i32** %cptr
+; CHECK-NOT: dereferenceable
+; CHECK: if.then:
+; CHECK: load i32, i32* %c, align 4
+
+define void @test10(i32* noalias %a, i32* %b, i32** dereferenceable(8) %cptr, i32 %n) #0 {
+entry:
+  %cmp11 = icmp sgt i32 %n, 0
+  br i1 %cmp11, label %for.body, label %for.end
+
+for.body:                                         ; preds = %entry, %for.inc
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv
+  %0 = load i32, i32* %arrayidx, align 4
+  %cmp1 = icmp sgt i32 %0, 0
+  br i1 %cmp1, label %if.then, label %for.inc
+
+if.then:                                          ; preds = %for.body
+  %c = load i32*, i32** %cptr, !dereferenceable !0
+  %1 = load i32, i32* %c, align 4
+  %arrayidx3 = getelementptr inbounds i32, i32* %b, i64 %indvars.iv
+  %2 = load i32, i32* %arrayidx3, align 4
+  %mul = mul nsw i32 %2, %1
+  store i32 %mul, i32* %arrayidx, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body, %if.then
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.inc, %entry
+  ret void
+}
+
 attributes #0 = { nounwind uwtable }
 !0 = !{i64 4}

diff --git a/test/Transforms/SimplifyCFG/SpeculativeExec.ll b/test/Transforms/SimplifyCFG/SpeculativeExec.ll
index c23a96d..73f9a0f 100644 (file)
--- a/test/Transforms/SimplifyCFG/SpeculativeExec.ll
+++ b/test/Transforms/SimplifyCFG/SpeculativeExec.ll
@@ -69,3 +69,29 @@ end:
 
   ret i8* %x10
 }
+
+define i32* @test5(i32 %a, i32 %b, i32 %c, i32* dereferenceable(10) %ptr1,
+                  i32* dereferenceable(10) %ptr2, i32** dereferenceable(10) %ptr3) nounwind {
+; CHECK-LABEL: @test5(
+entry:
+        %tmp1 = icmp eq i32 %b, 0
+        br i1 %tmp1, label %bb1, label %bb3
+
+bb1:            ; preds = %entry
+       %tmp2 = icmp sgt i32 %c, 1
+       br i1 %tmp2, label %bb2, label %bb3
+; CHECK: bb1:
+; CHECK-NEXT: icmp sgt i32 %c, 1
+; CHECK-NEXT: load i32*, i32** %ptr3
+; CHECK-NOT: dereferenceable
+; CHECK-NEXT: select i1 %tmp2, i32* %tmp3, i32* %ptr2
+; CHECK-NEXT: ret i32* %tmp3.ptr2
+
+bb2:           ; preds = bb1
+        %tmp3 = load i32*, i32** %ptr3, !dereferenceable !{i64 10}
+       br label %bb3
+
+bb3:           ; preds = %bb2, %entry
+       %tmp4 = phi i32* [ %ptr1, %entry ], [ %ptr2, %bb1 ], [ %tmp3, %bb2 ]
+       ret i32* %tmp4
+}