[ValueTracking] Enabling the patch 'an improvement for non-negative phi bits' by default

[olga.chupina]

Summary

Enabling the patch 'an improvement for non-negative phi bits' by default.
The patch was originally checked in under a flag: https://reviews.llvm.org/D18777
Performance issues were resolved. Enabling the patch as is.

[reames]

LGTM.

[olga.chupina]

Commit was reverted due to failing clang test.
After commit was reverted the test that was supposed to check my change was deleted from testing system.

So I'm uploading a new path.
The changes in lib/Analysis/ValueTracking.cpp are the same.
New changes:
I've fixed clang test: tools/clang/test/Frontend/optimization-remark-options.c
And added a new test in test/Analysis/ValueTracking folder, that checks my change.

Please review the updated patch.

Thanks in advance.

[olga.chupina]

updated patch is attached.

[olga.chupina]

Kindly ping.
Please, review updated patch and tests. Thanks.

[olga.chupina]

Please, review updated patch and tests. Thanks.

[olga.chupina]

Adding Hal Finkel as he was the last person updating llvm/tools/clang/test/Frontend/optimization-remark-options.c

[hfinkel]

In D34101#833685, @olga.chupina wrote:

Adding Hal Finkel as he was the last person updating llvm/tools/clang/test/Frontend/optimization-remark-options.c

Looks reasonable to me; go ahead and recommit.

cfe/trunk/test/Frontend/optimization-remark-options.c

 // RUN: %clang -O1 -fvectorize -target x86_64-unknown-unknown -Rpass-analysis=loop-vectorize -emit-llvm -S %s -o - 2>&1 | FileCheck %s
 
 // CHECK: {{.*}}:9:11: remark: loop not vectorized: cannot prove it is safe to reorder floating-point operations; allow reordering by specifying '#pragma clang loop vectorize(enable)' before the loop or by providing the compiler option '-ffast-math'.
 
 double foo(int N) {
   double v = 0.0;
 
   for (int i = 0; i < N; i++)
     v = v + 1.0;
 
   return v;
 }
 
 // CHECK: {{.*}}:17:3: remark: loop not vectorized: cannot prove it is safe to reorder memory operations; allow reordering by specifying '#pragma clang loop vectorize(enable)' before the loop. If the arrays will always be independent specify '#pragma clang loop vectorize(assume_safety)' before the loop or provide the '__restrict__' qualifier with the independent array arguments. Erroneous results will occur if these options are incorrectly applied!
 
 void foo2(int *dw, int *uw, int *A, int *B, int *C, int *D, int N) {
-  for (int i = 0; i < N; i++) {
+  for (long i = 0; i < N; i++) {
     dw[i] = A[i] + B[i - 1] + C[i - 2] + D[i - 3];
     uw[i] = A[i] + B[i + 1] + C[i + 2] + D[i + 3];
   }
 }