[LV] Inform about exactly reason of loop illegality

Currently, only the following information is provided by LoopVectorizer
in the case when the CF of the loop is not legal for vectorization:

 LV: Can't vectorize the instructions or CFG
    LV: Not vectorizing: Cannot prove legality.

But this information is not enough for the root cause analysis; what is
exactly wrong with the loop should also be printed:

 LV: Not vectorizing: The exiting block is not the loop latch.

Patch by Pavel Samolysov.

Reviewers: mkuper, hsaito, rengolin, fhahn

Reviewed By: fhahn

Differential Revision: https://reviews.llvm.org/D62311

llvm-svn: 362056

1 files changed, 0 insertions, 27 deletions

diff --git a/llvm/test/Transforms/LoopVectorize/legal_preheader_check.ll b/llvm/test/Transforms/LoopVectorize/legal_preheader_check.ll
deleted file mode 100644
index 32aa796394d..00000000000
--- a/llvm/test/Transforms/LoopVectorize/legal_preheader_check.ll
+++ /dev/null
@@ -1,27 +0,0 @@
-; RUN: opt < %s -loop-vectorize -debug -S -o /dev/null 2>&1 | FileCheck %s
-; REQUIRES: asserts
-
-; D40973
-; Make sure LV legal bails out when the loop doesn't have a legal pre-header.
-
-; CHECK: LV: Loop doesn't have a legal pre-header.
-
-define void @inc(i32 %n, i8* %P) {
-  %1 = icmp sgt i32 %n, 0
-  br i1 %1, label %BB1, label %BB2
-
-BB1:
-  indirectbr i8* %P, [label %.lr.ph]
-
-BB2:
-  br label %.lr.ph
-
-.lr.ph:
-  %indvars.iv = phi i32 [ %indvars.iv.next, %.lr.ph ], [ 0, %BB1 ], [ 0, %BB2 ]
-  %indvars.iv.next = add i32 %indvars.iv, 1
-  %exitcond = icmp eq i32 %indvars.iv.next, %n
-  br i1 %exitcond, label %._crit_edge, label %.lr.ph
-
-._crit_edge:
-  ret void
-}