AMDGPU: Change API for checking for exec modification
Invert the name and return value to better reflect the imprecise
nature.
Force passing in the DefMI, since it's known in the 2 users and could
possibly fail for an arbitrary vreg.
Allow specifying a specific user instruction. Scan through use
instructions, instead of use operands. Add scan thresholds instead of
searching infinitely.
Stop using a set to track seen uses. I didn't understand this usage,
or why it would not check the last use. I don't think the use list has
any particular order.
llvm-svn: 363675
diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
index 58f4d95..bb0076c 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -6073,28 +6073,49 @@
return nullptr;
}
-bool llvm::isEXECMaskConstantBetweenDefAndUses(unsigned VReg,
- const MachineRegisterInfo &MRI) {
+bool llvm::execMayBeModifiedBeforeUse(const MachineRegisterInfo &MRI,
+ unsigned VReg,
+ const MachineInstr &DefMI,
+ const MachineInstr *UseMI) {
assert(MRI.isSSA() && "Must be run on SSA");
+ assert(DefMI.definesRegister(VReg) && "wrong def instruction");
+
auto *TRI = MRI.getTargetRegisterInfo();
+ auto *DefBB = DefMI.getParent();
- auto *DefI = MRI.getVRegDef(VReg);
- auto *BB = DefI->getParent();
+ if (UseMI) {
+ // Don't bother searching between blocks, although it is possible this block
+ // doesn't modify exec.
+ if (UseMI->getParent() != DefBB)
+ return true;
+ } else {
+ int NumUse = 0;
+ const int MaxUseScan = 10;
- DenseSet<MachineInstr*> Uses;
- for (auto &Use : MRI.use_nodbg_operands(VReg)) {
- auto *I = Use.getParent();
- if (I->getParent() != BB)
- return false;
- Uses.insert(I);
+ for (auto &UseInst : MRI.use_nodbg_instructions(VReg)) {
+ if (UseInst.getParent() != DefBB)
+ return true;
+
+ if (NumUse++ > MaxUseScan)
+ return true;
+ }
}
- auto E = BB->end();
- for (auto I = std::next(DefI->getIterator()); I != E; ++I) {
- Uses.erase(&*I);
- // don't check the last use
- if (Uses.empty() || I->modifiesRegister(AMDGPU::EXEC, TRI))
- break;
+ const int MaxInstScan = 20;
+ int NumScan = 0;
+
+ // Stop scan at the use if known.
+ auto E = UseMI ? UseMI->getIterator() : DefBB->end();
+ for (auto I = std::next(DefMI.getIterator()); I != E; ++I) {
+ if (I->isDebugInstr())
+ continue;
+
+ if (NumScan++ > MaxInstScan)
+ return true;
+
+ if (I->modifiesRegister(AMDGPU::EXEC, TRI))
+ return true;
}
- return Uses.empty();
+
+ return false;
}