[llvm] [InstCombine] Handle ptrtoaddr in gep of pointer sub fold (PR #164818)

[Nikita Popov via llvm-commits]

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@@ -3315,21 +3315,21 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
 
       if (TyAllocSize == 1) {
         // Canonicalize (gep i8* X, (ptrtoint Y)-(ptrtoint X)) to (bitcast Y),
-        // but only if the result pointer is only used as if it were an integer,
-        // or both point to the same underlying object (otherwise provenance is
-        // not necessarily retained).
+        // but only if the result pointer is only used as if it were an integer.
+        // (The case where the underlying object is the same is handled by
+        // InstSimplify.)
         Value *X = GEP.getPointerOperand();
         Value *Y;
-        if (match(GEP.getOperand(1),
-                  m_Sub(m_PtrToInt(m_Value(Y)), m_PtrToInt(m_Specific(X)))) &&
+        if (match(GEP.getOperand(1), m_Sub(m_PtrToIntOrAddr(m_Value(Y)),
+                                           m_PtrToIntOrAddr(m_Specific(X)))) &&
             GEPType == Y->getType()) {
-          bool HasSameUnderlyingObject =
-              getUnderlyingObject(X) == getUnderlyingObject(Y);
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nikic wrote:

See https://github.com/llvm/llvm-project/blob/53b9441f5355fcdca07dc5b6ddc4fa5bb7ce4920/llvm/lib/Analysis/InstructionSimplify.cpp#L5117 for the InstSimplify transform that handles the same underlying object case, which is why I dropped the handling here.

https://github.com/llvm/llvm-project/pull/164818