[llvm] [VPlan] Add VPValue for VF, use it for VPWidenIntOrFpInductionRecipe. (PR #95305)

[David Sherwood via llvm-commits]

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@@ -385,8 +381,8 @@ define void @test_reversed_load2_store2(ptr noalias nocapture readonly %A, ptr n
 ; CHECK-NEXT:    [[TMP1:%.*]] = shl nuw nsw i64 [[TMP0]], 2
 ; CHECK-NEXT:    [[TMP2:%.*]] = call <vscale x 4 x i32> @llvm.experimental.stepvector.nxv4i32()
 ; CHECK-NEXT:    [[INDUCTION:%.*]] = sub <vscale x 4 x i32> shufflevector (<vscale x 4 x i32> insertelement (<vscale x 4 x i32> poison, i32 1023, i64 0), <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer), [[TMP2]]
-; CHECK-NEXT:    [[TMP3:%.*]] = call i32 @llvm.vscale.i32()
-; CHECK-NEXT:    [[DOTNEG:%.*]] = mul nsw i32 [[TMP3]], -4
+; CHECK-NEXT:    [[TMP3:%.*]] = trunc nuw nsw i64 [[TMP1]] to i32
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david-arm wrote:

In practice it probably doesn't matter since vscale is not unlikely to ever be that large, but the code after is not the same as before. Suppose vscale = 0xFFFFFFFF, then previously we'd be doing

0xFFFFFFFF (-1) * -4 -> +4

whereas now it would be


0xFFFFFFFF << 2 -> 0x3FFFFFFFC
trunc(0x3FFFFFFFC) to i32 -> 0xFFFFFFFC
0 - 0xFFFFFFFC -> poison due to nsw?

Perhaps the previous code was simply incorrect?

https://github.com/llvm/llvm-project/pull/95305