[llvm] [InstCombine] ptrmask of gep for dynamic pointer aligment (PR #80002)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Wed Jan 31 08:31:54 PST 2024
================
@@ -966,6 +966,41 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
I, 1, (DemandedMask & ~LHSKnown.Zero).zextOrTrunc(MaskWidth)))
return I;
+ // Combine:
+ // (ptrmask (getelementptr i8, ptr p, imm i), imm mask)
+ // -> (ptrmask (getelementptr i8, ptr p, imm (i & mask)), imm mask)
+ // where only the low bits known to be zero in the pointer are changed
+ Value *InnerPtr;
+ uint64_t GEPIndex;
+ uint64_t PtrMaskImmediate;
+ if (match(I, m_Intrinsic<Intrinsic::ptrmask>(
+ m_GEP(m_Value(InnerPtr), m_ConstantInt(GEPIndex)),
+ m_ConstantInt(PtrMaskImmediate)))) {
+ auto *GEP = cast<GetElementPtrInst>(II->getArgOperand(0));
+
+ if (GEP->getSourceElementType() == Type::getInt8Ty(I->getContext())) {
+ unsigned Log2Align = llvm::Log2(InnerPtr->getPointerAlignment(DL));
----------------
nikic wrote:
Instead of getPointerAlignment(), this should make use of `LHSKnown`. Please also add a test where the GEP operand isn't literally a function argument but say an alignment-preserving GEP of an argument.
https://github.com/llvm/llvm-project/pull/80002
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