[regalloc][LiveRegMatrix] Add validity check for LiveRegMatrix to prevent dangling pointers #168553
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…ointers - Implemented `isValid()` method in LiveRegMatrix to verify that all LiveInterval pointers are valid. - Added assertion in RegAllocBase's `postOptimization()` to ensure no dangling pointers exist in LiveRegMatrix after spilling.
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@llvm/pr-subscribers-llvm-regalloc Author: Valery Pykhtin (vpykhtin) Changes
This is for testing only, do not merge. It will be submitted as part of ongoing fix to prevent test failures. Full diff: https://github.com/llvm/llvm-project/pull/168553.diff 3 Files Affected:
diff --git a/llvm/include/llvm/CodeGen/LiveRegMatrix.h b/llvm/include/llvm/CodeGen/LiveRegMatrix.h
index 35add577d071a..a4a7c0375b9ab 100644
--- a/llvm/include/llvm/CodeGen/LiveRegMatrix.h
+++ b/llvm/include/llvm/CodeGen/LiveRegMatrix.h
@@ -170,6 +170,16 @@ class LiveRegMatrix {
}
Register getOneVReg(unsigned PhysReg) const;
+
+ /// Verify that all LiveInterval pointers in the matrix are valid.
+ /// This checks that each LiveInterval referenced in LiveIntervalUnion
+ /// actually exists in LiveIntervals and is not a dangling pointer.
+ /// Returns true if the matrix is valid, false if dangling pointers are found.
+ /// This is primarily useful for debugging heap-use-after-free issues.
+ /// This method uses a lazy approach - it builds a set of valid LiveInterval
+ /// pointers on-demand and has zero runtime/memory overhead during normal
+ /// register allocation.
+ bool isValid() const;
};
class LiveRegMatrixWrapperLegacy : public MachineFunctionPass {
diff --git a/llvm/lib/CodeGen/LiveRegMatrix.cpp b/llvm/lib/CodeGen/LiveRegMatrix.cpp
index e7238008d2c69..0f9571ea81389 100644
--- a/llvm/lib/CodeGen/LiveRegMatrix.cpp
+++ b/llvm/lib/CodeGen/LiveRegMatrix.cpp
@@ -12,11 +12,13 @@
#include "llvm/CodeGen/LiveRegMatrix.h"
#include "RegisterCoalescer.h"
+#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervalUnion.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
@@ -290,6 +292,33 @@ Register LiveRegMatrix::getOneVReg(unsigned PhysReg) const {
return MCRegister::NoRegister;
}
+bool LiveRegMatrix::isValid() const {
+ // Build set of all valid LiveInterval pointers from LiveIntervals.
+ DenseSet<LiveInterval *> ValidIntervals;
+ for (unsigned RegIdx = 0, NumRegs = VRM->getRegInfo().getNumVirtRegs();
+ RegIdx < NumRegs; ++RegIdx) {
+ Register VReg = Register::index2VirtReg(RegIdx);
+ // Only track assigned registers since unassigned ones won't be in Matrix
+ if (VRM->hasPhys(VReg) && LIS->hasInterval(VReg))
+ ValidIntervals.insert(&LIS->getInterval(VReg));
+ }
+
+ // Now scan all LiveIntervalUnions in the matrix and verify each pointer
+ unsigned NumDanglingPointers = 0;
+ for (unsigned I = 0, Size = Matrix.size(); I != Size; ++I) {
+ MCRegUnit Unit = static_cast<MCRegUnit>(I);
+ for (const LiveInterval *LI : Matrix[Unit]) {
+ if (!ValidIntervals.contains(LI)) {
+ ++NumDanglingPointers;
+ dbgs() << "ERROR: LiveInterval pointer is not found in LiveIntervals:\n"
+ << " Register Unit: " << printRegUnit(Unit, TRI) << '\n'
+ << " LiveInterval pointer: " << LI << '\n';
+ }
+ }
+ }
+ return NumDanglingPointers == 0;
+}
+
AnalysisKey LiveRegMatrixAnalysis::Key;
LiveRegMatrix LiveRegMatrixAnalysis::run(MachineFunction &MF,
diff --git a/llvm/lib/CodeGen/RegAllocBase.cpp b/llvm/lib/CodeGen/RegAllocBase.cpp
index 2400a1feea26e..9ba6007fc1cb9 100644
--- a/llvm/lib/CodeGen/RegAllocBase.cpp
+++ b/llvm/lib/CodeGen/RegAllocBase.cpp
@@ -155,6 +155,10 @@ void RegAllocBase::allocatePhysRegs() {
void RegAllocBase::postOptimization() {
spiller().postOptimization();
+
+ // Verify LiveRegMatrix after spilling (no dangling pointers).
+ assert(Matrix->isValid() && "LiveRegMatrix validation failed");
+
for (auto *DeadInst : DeadRemats) {
LIS->RemoveMachineInstrFromMaps(*DeadInst);
DeadInst->eraseFromParent();
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🐧 Linux x64 Test Results
Failed Tests(click on a test name to see its output) LLVMLLVM.CodeGen/AMDGPU/sgpr-spill-overlap-wwm-reserve.mirLLVM.CodeGen/ARM/splitkit.llLLVM.CodeGen/ARM/udivmodei5.llLLVM.CodeGen/Mips/hf16call32.llLLVM.CodeGen/Mips/stldst.llLLVM.CodeGen/Thumb2/constant-islands.llLLVM.CodeGen/X86/bittest-big-integer.llLLVM.CodeGen/X86/div-rem-pair-recomposition-signed.llLLVM.CodeGen/X86/fp-i129.llLLVM.CodeGen/X86/optimize-max-0.llLLVM.CodeGen/X86/pseudo_cmov_lower.llLLVM.CodeGen/X86/udivmodei5.llIf these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the |
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isValid()method in LiveRegMatrix to verify that all LiveInterval pointers are valid.postOptimization()to ensure no dangling pointers exist in LiveRegMatrix after spilling.This is for testing only, do not merge. It will be submitted as part of ongoing fix to prevent test failures.