[llvm] d7267ee - [ValueTracking] Let isGuaranteedNotToBeUndefOrPoison look into branch conditions of dominating blocks' terminators
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Thu Mar 5 08:13:30 PST 2020
On Thu, Mar 5, 2020 at 7:09 PM Juneyoung Lee via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
>
> Author: Juneyoung Lee
> Date: 2020-03-06T01:08:35+09:00
> New Revision: d7267ee1941668d7e985681e29d10983799811a0
>
> URL: https://github.com/llvm/llvm-project/commit/d7267ee1941668d7e985681e29d10983799811a0
> DIFF: https://github.com/llvm/llvm-project/commit/d7267ee1941668d7e985681e29d10983799811a0.diff
>
> LOG: [ValueTracking] Let isGuaranteedNotToBeUndefOrPoison look into branch conditions of dominating blocks' terminators
>
> Summary:
> ```
> br i1 c, BB1, BB2:
> BB1:
> use1(c)
> BB2:
> use2(c)
> ```
>
> In BB1 and BB2, c is never undef or poison because otherwise the branch would have triggered UB.
>
> This is a resubmission of 952ad47 with crash fix of llvm/test/Transforms/LoopRotate/freeze-crash.ll.
>
> Checked with Alive2
>
> Reviewers: xbolva00, spatel, lebedev.ri, reames, jdoerfert, nlopes, sanjoy
>
> Reviewed By: reames
>
> Subscribers: jdoerfert, hiraditya, llvm-commits
>
> Tags: #llvm
>
> Differential Revision: https://reviews.llvm.org/D75401
>
> Added:
>
>
> Modified:
> llvm/include/llvm/Analysis/ValueTracking.h
> llvm/lib/Analysis/InstructionSimplify.cpp
> llvm/lib/Analysis/ValueTracking.cpp
> llvm/test/Transforms/InstSimplify/freeze.ll
>
> Removed:
>
>
>
> ################################################################################
> diff --git a/llvm/include/llvm/Analysis/ValueTracking.h b/llvm/include/llvm/Analysis/ValueTracking.h
> index 3a4fe8bdc199..dc28d2375a78 100644
> --- a/llvm/include/llvm/Analysis/ValueTracking.h
> +++ b/llvm/include/llvm/Analysis/ValueTracking.h
> @@ -569,7 +569,13 @@ class Value;
>
> /// Return true if this function can prove that V is never undef value
> /// or poison value.
> - bool isGuaranteedNotToBeUndefOrPoison(const Value *V);
> + //
> + /// If CtxI and DT are specified this method performs flow-sensitive analysis
> + /// and returns true if it is guaranteed to be never undef or poison
> + /// immediately before the CtxI.
> + bool isGuaranteedNotToBeUndefOrPoison(const Value *V,
> + const Instruction *CtxI = nullptr,
> + const DominatorTree *DT = nullptr);
>
> /// Specific patterns of select instructions we can match.
> enum SelectPatternFlavor {
>
> diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
> index 9fa78f369d0e..137f7455b65a 100644
> --- a/llvm/lib/Analysis/InstructionSimplify.cpp
> +++ b/llvm/lib/Analysis/InstructionSimplify.cpp
> @@ -5360,16 +5360,16 @@ Value *llvm::SimplifyCall(CallBase *Call, const SimplifyQuery &Q) {
> }
>
> /// Given operands for a Freeze, see if we can fold the result.
> -static Value *SimplifyFreezeInst(Value *Op0) {
> +static Value *SimplifyFreezeInst(Value *Op0, const SimplifyQuery &Q) {
> // Use a utility function defined in ValueTracking.
> - if (llvm::isGuaranteedNotToBeUndefOrPoison(Op0))
> + if (llvm::isGuaranteedNotToBeUndefOrPoison(Op0, Q.CxtI, Q.DT))
> return Op0;
> // We have room for improvement.
> return nullptr;
> }
>
> Value *llvm::SimplifyFreezeInst(Value *Op0, const SimplifyQuery &Q) {
> - return ::SimplifyFreezeInst(Op0);
> + return ::SimplifyFreezeInst(Op0, Q);
> }
>
> /// See if we can compute a simplified version of this instruction.
>
> diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
> index e11f5e2a8397..d46a5d998f5b 100644
> --- a/llvm/lib/Analysis/ValueTracking.cpp
> +++ b/llvm/lib/Analysis/ValueTracking.cpp
> @@ -4525,7 +4525,9 @@ bool llvm::isOverflowIntrinsicNoWrap(const WithOverflowInst *WO,
> return llvm::any_of(GuardingBranches, AllUsesGuardedByBranch);
> }
>
> -bool llvm::isGuaranteedNotToBeUndefOrPoison(const Value *V) {
> +bool llvm::isGuaranteedNotToBeUndefOrPoison(const Value *V,
> + const Instruction *CtxI,
> + const DominatorTree *DT) {
> // If the value is a freeze instruction, then it can never
> // be undef or poison.
> if (isa<FreezeInst>(V))
> @@ -4558,6 +4560,30 @@ bool llvm::isGuaranteedNotToBeUndefOrPoison(const Value *V) {
> return true;
> }
>
> + // CxtI may be null or a cloned instruction.
> + if (!CtxI || !CtxI->getParent() || !DT)
> + return false;
> +
> + // If V is used as a branch condition before reaching CtxI, V cannot be
> + // undef or poison.
> + // br V, BB1, BB2
> + // BB1:
> + // CtxI ; V cannot be undef or poison here
> + auto Dominator = DT->getNode(CtxI->getParent())->getIDom();
> + while (Dominator) {
> + auto *TI = Dominator->getBlock()->getTerminator();
> +
> + if (auto BI = dyn_cast<BranchInst>(TI)) {
> + if (BI->isConditional() && BI->getCondition() == V)
> + return true;
> + } else if (auto SI = dyn_cast<SwitchInst>(TI)) {
> + if (SI->getCondition() == V)
> + return true;
> + }
> +
> + Dominator = Dominator->getIDom();
> + }
> +
> return false;
> }
>
>
> diff --git a/llvm/test/Transforms/InstSimplify/freeze.ll b/llvm/test/Transforms/InstSimplify/freeze.ll
> index ac287b949f07..e6085bf392bf 100644
> --- a/llvm/test/Transforms/InstSimplify/freeze.ll
> +++ b/llvm/test/Transforms/InstSimplify/freeze.ll
> @@ -18,3 +18,66 @@ define i32 @make_const() {
> %x = freeze i32 10
> ret i32 %x
> }
> +
> +define i1 @brcond(i1 %c, i1 %c2) {
> +; CHECK-LABEL: @brcond(
> +; CHECK-NEXT: br i1 [[C:%.*]], label [[A:%.*]], label [[B:%.*]]
> +; CHECK: A:
> +; CHECK-NEXT: br i1 [[C2:%.*]], label [[A2:%.*]], label [[B]]
> +; CHECK: A2:
> +; CHECK-NEXT: ret i1 [[C]]
> +; CHECK: B:
> +; CHECK-NEXT: ret i1 [[C]]
> +;
> + br i1 %c, label %A, label %B
> +A:
> + br i1 %c2, label %A2, label %B
> +A2:
> + %f1 = freeze i1 %c
> + ret i1 %f1
> +B:
> + %f2 = freeze i1 %c
> + ret i1 %f2
> +}
> +
> +define i32 @brcond_switch(i32 %x) {
> +; CHECK-LABEL: @brcond_switch(
> +; CHECK-NEXT: switch i32 [[X:%.*]], label [[EXIT:%.*]] [
> +; CHECK-NEXT: i32 0, label [[A:%.*]]
> +; CHECK-NEXT: ]
> +; CHECK: A:
> +; CHECK-NEXT: ret i32 [[X]]
> +; CHECK: EXIT:
> +; CHECK-NEXT: ret i32 [[X]]
> +;
> + switch i32 %x, label %EXIT [ i32 0, label %A ]
> +A:
> + %fr1 = freeze i32 %x
> + ret i32 %fr1
> +EXIT:
> + %fr2 = freeze i32 %x
> + ret i32 %fr2
> +}
> +
> +define i1 @brcond_noopt(i1 %c, i1 %c2) {
> +; CHECK-LABEL: @brcond_noopt(
> +; CHECK-NEXT: [[F:%.*]] = freeze i1 [[C:%.*]]
> +; CHECK-NEXT: call void @f1(i1 [[F]])
> +; CHECK-NEXT: call void @f2()
> +; CHECK-NEXT: br i1 [[C]], label [[A:%.*]], label [[B:%.*]]
> +; CHECK: A:
> +; CHECK-NEXT: ret i1 false
> +; CHECK: B:
> +; CHECK-NEXT: ret i1 true
> +;
> + %f = freeze i1 %c
> + call void @f1(i1 %f) ; cannot optimize i1 %f to %c
> + call void @f2() ; .. because if f2() exits, `br %c` cannot be reached
> + br i1 %c, label %A, label %B
> +A:
> + ret i1 0
> +B:
> + ret i1 1
> +}
> +declare void @f1(i1)
> +declare void @f2()
In all future patches, please, unless the testcase is crashing without
the patch, please do commit the testcase first, so that the patch
only shows the changed check-lines in the tests, not just introduces
whole new tests.
This way the tests won't get lost when the patch is reverted, too.
Roman
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