[llvm] [polly] [InstCombine] Canonicalise SextADD + GEP (PR #69581)

[Nikita Popov via llvm-commits]

================
@@ -2335,6 +2335,20 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
       return GetElementPtrInst::Create(GEP.getResultElementType(), NewPtr,
                                        Idx2);
     }
+
+    ConstantInt *C;
+    if (match(GEP.getOperand(1), m_OneUse(m_SExt(m_OneUse(m_NSWAdd(
+                                     m_Value(Idx1), m_ConstantInt(C))))))) {
+      // %add = add nsw i32 %idx1, idx2
+      // %sidx = sext i32 %add to i64
+      // %gep = getelementptr i32, i32* %ptr, i64 %sidx
+      // as :
+      // %newptr = getelementptr i32, i32* %ptr, i32 %idx1
+      // %newgep = getelementptr i32, i32* %newptr, i32 idx2
----------------
nikic wrote:

```suggestion
      // %gep = getelementptr i32, ptr %ptr, i64 %sidx
      // as:
      // %newptr = getelementptr i32, ptr %ptr, i32 %idx1
      // %newgep = getelementptr i32, ptr %newptr, i32 idx2
```

https://github.com/llvm/llvm-project/pull/69581