[llvm] r290763 - [MemDep] Handle gep with zeros for invariant.group
Piotr Padlewski via llvm-commits
llvm-commits at lists.llvm.org
Fri Dec 30 10:45:08 PST 2016
Author: prazek
Date: Fri Dec 30 12:45:07 2016
New Revision: 290763
URL: http://llvm.org/viewvc/llvm-project?rev=290763&view=rev
Log:
[MemDep] Handle gep with zeros for invariant.group
Summary:
gep 0, 0 is equivalent to bitcast. LLVM canonicalizes it
to getelementptr because it make SROA can then handle it.
Simple case like
void g(A &a) {
z(a);
if (glob)
a.foo();
}
void testG() {
A a;
g(a);
}
was not devirtualized with -fstrict-vtable-pointers because luck of
handling for gep 0 in Memory Dependence Analysis
Reviewers: dberlin, nlewycky, chandlerc
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D28126
Modified:
llvm/trunk/docs/LangRef.rst
llvm/trunk/lib/Analysis/MemoryDependenceAnalysis.cpp
llvm/trunk/test/Transforms/GVN/invariant.group.ll
llvm/trunk/test/Transforms/NewGVN/invariant.group.ll
Modified: llvm/trunk/docs/LangRef.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/LangRef.rst?rev=290763&r1=290762&r2=290763&view=diff
==============================================================================
--- llvm/trunk/docs/LangRef.rst (original)
+++ llvm/trunk/docs/LangRef.rst Fri Dec 30 12:45:07 2016
@@ -4904,7 +4904,8 @@ The existence of the ``invariant.group``
the optimizer that every ``load`` and ``store`` to the same pointer operand
within the same invariant group can be assumed to load or store the same
value (but see the ``llvm.invariant.group.barrier`` intrinsic which affects
-when two pointers are considered the same).
+when two pointers are considered the same). Pointers returned by bitcast or
+getelementptr with only zero indices are considered the same.
Examples:
Modified: llvm/trunk/lib/Analysis/MemoryDependenceAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemoryDependenceAnalysis.cpp?rev=290763&r1=290762&r2=290763&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/MemoryDependenceAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/MemoryDependenceAnalysis.cpp Fri Dec 30 12:45:07 2016
@@ -339,43 +339,62 @@ MemDepResult MemoryDependenceResults::ge
MemDepResult
MemoryDependenceResults::getInvariantGroupPointerDependency(LoadInst *LI,
BasicBlock *BB) {
+
+ auto *InvariantGroupMD = LI->getMetadata(LLVMContext::MD_invariant_group);
+ if (!InvariantGroupMD)
+ return MemDepResult::getUnknown();
+
Value *LoadOperand = LI->getPointerOperand();
// It's is not safe to walk the use list of global value, because function
// passes aren't allowed to look outside their functions.
if (isa<GlobalValue>(LoadOperand))
return MemDepResult::getUnknown();
- auto *InvariantGroupMD = LI->getMetadata(LLVMContext::MD_invariant_group);
- if (!InvariantGroupMD)
- return MemDepResult::getUnknown();
-
- SmallSet<Value *, 14> Seen;
// Queue to process all pointers that are equivalent to load operand.
- SmallVector<Value *, 8> LoadOperandsQueue;
- LoadOperandsQueue.push_back(LoadOperand);
- Seen.insert(LoadOperand);
+ SmallVector<const Value *, 8> LoadOperandsQueue;
+ SmallSet<const Value *, 14> SeenValues;
+ auto TryInsertToQueue = [&](Value *V) {
+ if (SeenValues.insert(V).second)
+ LoadOperandsQueue.push_back(V);
+ };
+
+ TryInsertToQueue(LoadOperand);
while (!LoadOperandsQueue.empty()) {
- Value *Ptr = LoadOperandsQueue.pop_back_val();
+ const Value *Ptr = LoadOperandsQueue.pop_back_val();
+ assert(Ptr);
if (isa<GlobalValue>(Ptr))
continue;
- if (auto *BCI = dyn_cast<BitCastInst>(Ptr)) {
- if (Seen.insert(BCI->getOperand(0)).second) {
- LoadOperandsQueue.push_back(BCI->getOperand(0));
- }
- }
+ // Value comes from bitcast: Ptr = bitcast x. Insert x.
+ if (auto *BCI = dyn_cast<BitCastInst>(Ptr))
+ TryInsertToQueue(BCI->getOperand(0));
+ // Gep with zeros is equivalent to bitcast.
+ // FIXME: we are not sure if some bitcast should be canonicalized to gep 0
+ // or gep 0 to bitcast because of SROA, so there are 2 forms. When typeless
+ // pointers will be upstream then both cases will be gone (and this BFS
+ // also won't be needed).
+ if (auto *GEP = dyn_cast<GetElementPtrInst>(Ptr))
+ if (GEP->hasAllZeroIndices())
+ TryInsertToQueue(GEP->getOperand(0));
- for (Use &Us : Ptr->uses()) {
+ for (const Use &Us : Ptr->uses()) {
auto *U = dyn_cast<Instruction>(Us.getUser());
if (!U || U == LI || !DT.dominates(U, LI))
continue;
- if (auto *BCI = dyn_cast<BitCastInst>(U)) {
- if (Seen.insert(BCI).second) {
- LoadOperandsQueue.push_back(BCI);
- }
+ // Bitcast or gep with zeros are using Ptr. Add to queue to check it's
+ // users. U = bitcast Ptr
+ if (isa<BitCastInst>(U)) {
+ TryInsertToQueue(U);
continue;
}
+ // U = getelementptr Ptr, 0, 0...
+ if (auto *GEP = dyn_cast<GetElementPtrInst>(U))
+ if (GEP->hasAllZeroIndices()) {
+ TryInsertToQueue(U);
+ continue;
+ }
+
// If we hit load/store with the same invariant.group metadata (and the
// same pointer operand) we can assume that value pointed by pointer
// operand didn't change.
Modified: llvm/trunk/test/Transforms/GVN/invariant.group.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GVN/invariant.group.ll?rev=290763&r1=290762&r2=290763&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/GVN/invariant.group.ll (original)
+++ llvm/trunk/test/Transforms/GVN/invariant.group.ll Fri Dec 30 12:45:07 2016
@@ -319,6 +319,31 @@ entry:
ret i8 %d
}
+; This test checks if invariant.group understands gep with zeros
+; CHECK-LABEL: define void @testGEP0() {
+define void @testGEP0() {
+ %a = alloca %struct.A, align 8
+ %1 = bitcast %struct.A* %a to i8*
+ %2 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 0
+ store i32 (...)** bitcast (i8** getelementptr inbounds ([3 x i8*], [3 x i8*]* @_ZTV1A, i64 0, i64 2) to i32 (...)**), i32 (...)*** %2, align 8, !invariant.group !0
+; CHECK: call void @_ZN1A3fooEv(%struct.A* nonnull dereferenceable(8) %a)
+ call void @_ZN1A3fooEv(%struct.A* nonnull dereferenceable(8) %a) ; This call may change vptr
+ %3 = load i8, i8* @unknownPtr, align 4
+ %4 = icmp eq i8 %3, 0
+ br i1 %4, label %_Z1gR1A.exit, label %5
+
+; This should be devirtualized by invariant.group
+ %6 = bitcast %struct.A* %a to void (%struct.A*)***
+ %7 = load void (%struct.A*)**, void (%struct.A*)*** %6, align 8, !invariant.group !0
+ %8 = load void (%struct.A*)*, void (%struct.A*)** %7, align 8
+; CHECK: call void @_ZN1A3fooEv(%struct.A* nonnull %a)
+ call void %8(%struct.A* nonnull %a)
+ br label %_Z1gR1A.exit
+
+_Z1gR1A.exit: ; preds = %0, %5
+ ret void
+}
+
declare void @foo(i8*)
declare void @bar(i8)
declare i8* @getPointer(i8*)
Modified: llvm/trunk/test/Transforms/NewGVN/invariant.group.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/NewGVN/invariant.group.ll?rev=290763&r1=290762&r2=290763&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/NewGVN/invariant.group.ll (original)
+++ llvm/trunk/test/Transforms/NewGVN/invariant.group.ll Fri Dec 30 12:45:07 2016
@@ -320,6 +320,31 @@ entry:
ret i8 %d
}
+; This test checks if invariant.group understands gep with zeros
+; CHECK-LABEL: define void @testGEP0() {
+define void @testGEP0() {
+ %a = alloca %struct.A, align 8
+ %1 = bitcast %struct.A* %a to i8*
+ %2 = getelementptr inbounds %struct.A, %struct.A* %a, i64 0, i32 0
+ store i32 (...)** bitcast (i8** getelementptr inbounds ([3 x i8*], [3 x i8*]* @_ZTV1A, i64 0, i64 2) to i32 (...)**), i32 (...)*** %2, align 8, !invariant.group !0
+; CHECK: call void @_ZN1A3fooEv(%struct.A* nonnull dereferenceable(8) %a)
+ call void @_ZN1A3fooEv(%struct.A* nonnull dereferenceable(8) %a) ; This call may change vptr
+ %3 = load i8, i8* @unknownPtr, align 4
+ %4 = icmp eq i8 %3, 0
+ br i1 %4, label %_Z1gR1A.exit, label %5
+
+; This should be devirtualized by invariant.group
+ %6 = bitcast %struct.A* %a to void (%struct.A*)***
+ %7 = load void (%struct.A*)**, void (%struct.A*)*** %6, align 8, !invariant.group !0
+ %8 = load void (%struct.A*)*, void (%struct.A*)** %7, align 8
+; CHECK: call void @_ZN1A3fooEv(%struct.A* nonnull %a)
+ call void %8(%struct.A* nonnull %a)
+ br label %_Z1gR1A.exit
+
+_Z1gR1A.exit: ; preds = %0, %5
+ ret void
+}
+
declare void @foo(i8*)
declare void @bar(i8)
declare i8* @getPointer(i8*)
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