[llvm] [SCEVExpander] Support hoisting udiv X, Y where Y is non-zero (PR #96102)

[Nikita Popov via llvm-commits]

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@@ -11,26 +11,29 @@ define void @test(i16 %x, i64 %y, ptr %ptr) {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[CONV19:%.*]] = sext i16 [[X:%.*]] to i64
 ; CHECK-NEXT:    [[ADD:%.*]] = add i64 [[CONV19]], 492802768830814067
+; CHECK-NEXT:    [[TMP0:%.*]] = udiv i64 [[Y:%.*]], [[ADD]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add nuw nsw i64 [[TMP0]], 4
+; CHECK-NEXT:    [[TMP2:%.*]] = add nuw nsw i64 [[TMP0]], 1
+; CHECK-NEXT:    [[TMP3:%.*]] = udiv i64 [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    [[TMP4:%.*]] = add nuw nsw i64 [[TMP3]], 1
+; CHECK-NEXT:    [[TMP5:%.*]] = add nuw nsw i64 [[TMP0]], 1
 ; CHECK-NEXT:    br label [[LOOP_PREHEADER:%.*]]
 ; CHECK:       loop.preheader:
-; CHECK-NEXT:    [[DIV:%.*]] = udiv i64 [[Y:%.*]], [[ADD]]
+; CHECK-NEXT:    [[DIV:%.*]] = udiv i64 [[Y]], [[ADD]]
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nikic wrote:

Why are we generating two divisions now, one in entry and one in the preheader?

https://github.com/llvm/llvm-project/pull/96102