[llvm] [AArch64][LoopVectorize] Use upper bound trip count instead of the constant TC when choosing max VF (PR #67697)

[via llvm-commits]

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@@ -0,0 +1,31 @@
+; RUN: opt -S < %s -passes=loop-vectorize -mtriple aarch64-linux-gnu -mattr=+sve 2>&1 | FileCheck %s
+
+define void @clamped_tc_8(ptr nocapture %dst, i32 %n, i64 %val){
+; CHECK-LABEL: define void @clamped_tc_8
+; CHECK: call void @llvm.masked.store.nxv8i8.p0(<vscale x 8 x i8> %19, ptr %20, i32 1, <vscale x 8 x i1> %active.lane.mask)
+entry:
+  %rem = and i32 %n, 63
+  %cmp8.not = icmp eq i32 %rem, 0
+  br i1 %cmp8.not, label %for.cond.cleanup, label %for.body.preheader
+
+for.body.preheader:                               ; preds = %entry
+  %add = add nuw nsw i32 %rem, 7
+  %shr = lshr i32 %add, 3
+  %wide.trip.count = zext i32 %shr to i64
+  br label %for.body
+
+for.body:                                         ; preds = %for.body.preheader, %for.body
+  %indvars.iv = phi i64 [ 0, %for.body.preheader ], [ %indvars.iv.next, %for.body ]
+  %p_out_tail.09 = phi ptr [ %dst, %for.body.preheader ], [ %incdec.ptr, %for.body ]
+  %0 = shl nuw nsw i64 %indvars.iv, 3
+  %shr3 = lshr i64 %val, %0
+  %conv4 = trunc i64 %shr3 to i8
+  store i8 %conv4, ptr %p_out_tail.09, align 1
+  %incdec.ptr = getelementptr inbounds i8, ptr %p_out_tail.09, i64 1
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond.not = icmp eq i64 %indvars.iv.next, 8
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Rin18 wrote:

> You probably want another version of this test that uses '%wide.trip.count' as the trip count, since we know the maximum for that is 8.
I see that we should use the'%wide.trip.count' variable instead of hardcoding 8 here. Should we have a different TC value or is this still fine to be 8 here?

https://github.com/llvm/llvm-project/pull/67697