[llvm] [SCEV] Try to re-use pointer LCSSA phis when expanding SCEVs. (PR #147824)

[Florian Hahn via llvm-commits]

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@@ -56,19 +56,16 @@ define void @test(ptr %arg, i64 %arg1) {
 ; CHECK-NEXT:    [[GEP_5:%.*]] = getelementptr inbounds double, ptr [[LCSSA_PTR_IV_1]], i64 1
 ; CHECK-NEXT:    br label [[INNER_2:%.*]]
 ; CHECK:       inner.2:
-; CHECK-NEXT:    [[INDVAR:%.*]] = phi i64 [ [[INDVAR_NEXT:%.*]], [[INNER_2]] ], [ 0, [[INNER_1_EXIT]] ]
 ; CHECK-NEXT:    [[PTR_IV_2:%.*]] = phi ptr [ [[GEP_5]], [[INNER_1_EXIT]] ], [ [[PTR_IV_2_NEXT:%.*]], [[INNER_2]] ]
 ; CHECK-NEXT:    [[PTR_IV_2_NEXT]] = getelementptr inbounds double, ptr [[PTR_IV_2]], i64 1
-; CHECK-NEXT:    [[INDVAR_NEXT]] = add i64 [[INDVAR]], 1
 ; CHECK-NEXT:    br i1 false, label [[INNER_3_LVER_CHECK:%.*]], label [[INNER_2]]
 ; CHECK:       inner.3.lver.check:
-; CHECK-NEXT:    [[INDVAR_LCSSA:%.*]] = phi i64 [ [[INDVAR]], [[INNER_2]] ]
 ; CHECK-NEXT:    [[LCSSA_PTR_IV_2:%.*]] = phi ptr [ [[PTR_IV_2]], [[INNER_2]] ]
 ; CHECK-NEXT:    [[GEP_6:%.*]] = getelementptr inbounds double, ptr [[PTR_PHI]], i64 1
 ; CHECK-NEXT:    [[GEP_7:%.*]] = getelementptr inbounds double, ptr [[LCSSA_PTR_IV_2]], i64 1
-; CHECK-NEXT:    [[TMP0:%.*]] = shl i64 [[INDVAR_LCSSA]], 3
-; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[TMP0]], 24
-; CHECK-NEXT:    [[SCEVGEP:%.*]] = getelementptr i8, ptr [[LCSSA_PTR_IV_1]], i64 [[TMP1]]
+; CHECK-NEXT:    [[TMP0:%.*]] = ptrtoint ptr [[LCSSA_PTR_IV_2]] to i64
+; CHECK-NEXT:    [[TMP1:%.*]] = add i64 [[TMP0]], 16
+; CHECK-NEXT:    [[SCEVGEP:%.*]] = inttoptr i64 [[TMP1]] to ptr
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fhahn wrote:

Yep updated to emit a GEP in that case. If the expression itself is used as int again, doing to `ptrtoint + add` is a bit more compact, but there's no easy way to detect this at this point.

https://github.com/llvm/llvm-project/pull/147824