[llvm] [ValueTracking] AllowEphemerals for alignment assumptions. (PR #108632)

[David Sherwood via llvm-commits]

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@@ -1693,6 +1690,179 @@ exit:
   ret void
 }
 
+; Variant of @ptr_induction_early_exit_eq_1 with alignment info via load metadata.
+define void @ptr_induction_early_exit_eq_1_with_align_on_load(ptr %a, ptr %b, ptr %c) {
+; CHECK-LABEL: 'ptr_induction_early_exit_eq_1_with_align_on_load'
+; CHECK-NEXT:  Classifying expressions for: @ptr_induction_early_exit_eq_1_with_align_on_load
+; CHECK-NEXT:    %a_ = load ptr, ptr %a, align 8, !align !0
+; CHECK-NEXT:    --> %a_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
+; CHECK-NEXT:    %b_ = load ptr, ptr %b, align 8, !align !0
+; CHECK-NEXT:    --> %b_ U: [0,-7) S: [-9223372036854775808,9223372036854775801)
+; CHECK-NEXT:    %ptr.iv = phi ptr [ %ptr.iv.next, %loop.inc ], [ %a_, %entry ]
+; CHECK-NEXT:    --> {%a_,+,8}<nuw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT:    %ld1 = load ptr, ptr %ptr.iv, align 8
+; CHECK-NEXT:    --> %ld1 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
+; CHECK-NEXT:    %ptr.iv.next = getelementptr inbounds i8, ptr %ptr.iv, i64 8
+; CHECK-NEXT:    --> {(8 + %a_),+,8}<nw><%loop> U: [0,-7) S: [-9223372036854775808,9223372036854775801) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT:  Determining loop execution counts for: @ptr_induction_early_exit_eq_1_with_align_on_load
+; CHECK-NEXT:  Loop %loop: <multiple exits> Unpredictable backedge-taken count.
+; CHECK-NEXT:    exit count for loop: ***COULDNOTCOMPUTE***
+; CHECK-NEXT:    exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+; CHECK-NEXT:  Loop %loop: constant max backedge-taken count is i64 2305843009213693951
+; CHECK-NEXT:  Loop %loop: symbolic max backedge-taken count is ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+; CHECK-NEXT:    symbolic max exit count for loop: ***COULDNOTCOMPUTE***
+; CHECK-NEXT:    symbolic max exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a_ to i64)) + (ptrtoint ptr %b_ to i64)) /u 8)
+;
+entry:
+  %a_ = load ptr, ptr %a, !align !{i64 8}
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david-arm wrote:

OK thanks for explaining!

https://github.com/llvm/llvm-project/pull/108632