[llvm] [SCEV] Use power of two facts involving vscale when inferring wrap flags (PR #101380)

[Philip Reames via llvm-commits]

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@@ -411,15 +412,16 @@ define void @vscalex4_ult_noflags(ptr nocapture %A, i32 %n) mustprogress vscale_
 ; CHECK-NEXT:    %VF = mul i32 %vscale, 4
 ; CHECK-NEXT:    --> (4 * vscale)<nuw><nsw> U: [8,4097) S: [8,4097)
 ; CHECK-NEXT:    %i.05 = phi i32 [ %add, %for.body ], [ 0, %entry ]
-; CHECK-NEXT:    --> {0,+,(4 * vscale)<nuw><nsw>}<%for.body> U: [0,-3) S: [-2147483648,2147483645) Exits: <<Unknown>> LoopDispositions: { %for.body: Computable }
+; CHECK-NEXT:    --> {0,+,(4 * vscale)<nuw><nsw>}<%for.body> U: [0,-3) S: [-2147483648,2147483645) Exits: (4 * vscale * ((-1 + %n) /u (4 * vscale)<nuw><nsw>)) LoopDispositions: { %for.body: Computable }
 ; CHECK-NEXT:    %arrayidx = getelementptr inbounds i32, ptr %A, i32 %i.05
-; CHECK-NEXT:    --> {%A,+,(16 * vscale)<nuw><nsw>}<%for.body> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %for.body: Computable }
+; CHECK-NEXT:    --> {%A,+,(16 * vscale)<nuw><nsw>}<%for.body> U: full-set S: full-set Exits: ((16 * vscale * ((-1 + %n) /u (4 * vscale)<nuw><nsw>)) + %A) LoopDispositions: { %for.body: Computable }
 ; CHECK-NEXT:    %add = add i32 %i.05, %VF
-; CHECK-NEXT:    --> {(4 * vscale)<nuw><nsw>,+,(4 * vscale)<nuw><nsw>}<%for.body> U: [0,-3) S: [-2147483648,2147483645) Exits: <<Unknown>> LoopDispositions: { %for.body: Computable }
+; CHECK-NEXT:    --> {(4 * vscale)<nuw><nsw>,+,(4 * vscale)<nuw><nsw>}<nw><%for.body> U: [0,-3) S: [-2147483648,2147483645) Exits: (vscale * (4 + (4 * ((-1 + %n) /u (4 * vscale)<nuw><nsw>))<nuw><nsw>)<nuw>) LoopDispositions: { %for.body: Computable }
 ; CHECK-NEXT:  Determining loop execution counts for: @vscalex4_ult_noflags
-; CHECK-NEXT:  Loop %for.body: Unpredictable backedge-taken count.
-; CHECK-NEXT:  Loop %for.body: Unpredictable constant max backedge-taken count.
-; CHECK-NEXT:  Loop %for.body: Unpredictable symbolic max backedge-taken count.
+; CHECK-NEXT:  Loop %for.body: backedge-taken count is ((-1 + %n) /u (4 * vscale)<nuw><nsw>)
+; CHECK-NEXT:  Loop %for.body: constant max backedge-taken count is i32 536870910
+; CHECK-NEXT:  Loop %for.body: symbolic max backedge-taken count is ((-1 + %n) /u (4 * vscale)<nuw><nsw>)
+; CHECK-NEXT:  Loop %for.body: Trip multiple is 1
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preames wrote:

Yes.  This change only includes the existing power-of-two cases.  We need to handle negative power of two as well to infer no-self-wrap for these, which will be a separate patch.

https://github.com/llvm/llvm-project/pull/101380