[llvm] r252604 - Strip metadata when speculatively hoisting instructions
Igor Laevsky via llvm-commits
llvm-commits at lists.llvm.org
Tue Nov 10 06:10:32 PST 2015
Author: igor.laevsky
Date: Tue Nov 10 08:10:31 2015
New Revision: 252604
URL: http://llvm.org/viewvc/llvm-project?rev=252604&view=rev
Log:
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
Modified:
llvm/trunk/lib/Analysis/LoopInfo.cpp
llvm/trunk/lib/Transforms/Scalar/LICM.cpp
llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/licm.ll
llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll
llvm/trunk/test/Transforms/SimplifyCFG/SpeculativeExec.ll
Modified: llvm/trunk/lib/Analysis/LoopInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/LoopInfo.cpp?rev=252604&r1=252603&r2=252604&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/LoopInfo.cpp (original)
+++ llvm/trunk/lib/Analysis/LoopInfo.cpp Tue Nov 10 08:10:31 2015
@@ -120,6 +120,13 @@ bool Loop::makeLoopInvariant(Instruction
// 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;
}
Modified: llvm/trunk/lib/Transforms/Scalar/LICM.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LICM.cpp?rev=252604&r1=252603&r2=252604&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LICM.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LICM.cpp Tue Nov 10 08:10:31 2015
@@ -672,6 +672,10 @@ static bool hoist(Instruction &I, BasicB
// 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;
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=252604&r1=252603&r2=252604&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Tue Nov 10 08:10:31 2015
@@ -1618,6 +1618,11 @@ static bool SpeculativelyExecuteBB(Branc
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()));
Modified: llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/licm.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/licm.ll?rev=252604&r1=252603&r2=252604&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/licm.ll (original)
+++ llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/licm.ll Tue Nov 10 08:10:31 2015
@@ -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
Modified: llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll?rev=252604&r1=252603&r2=252604&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll (original)
+++ llvm/trunk/test/Transforms/LICM/hoist-deref-load.ll Tue Nov 10 08:10:31 2015
@@ -388,5 +388,49 @@ for.end:
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}
Modified: llvm/trunk/test/Transforms/SimplifyCFG/SpeculativeExec.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/SpeculativeExec.ll?rev=252604&r1=252603&r2=252604&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/SpeculativeExec.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/SpeculativeExec.ll Tue Nov 10 08:10:31 2015
@@ -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
+}
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