[llvm] [InstCombine] ptrmask of gep for dynamic pointer aligment (PR #80002)

[via llvm-commits]

================
@@ -966,6 +966,48 @@ 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)),
----------------
goldsteinn wrote:

Instead of matching `GEP` then checking its `i8` think you can just use `m_PtrAdd`.

https://github.com/llvm/llvm-project/pull/80002