From d97136c182a5832b61b036c4537f38ac603345ef Mon Sep 17 00:00:00 2001
From: Nikolai Bozhenov <nikolai.bozhenov@intel.com>
Date: Thu, 10 Aug 2017 11:24:57 +0000
Subject: [PATCH] [ValueTracking] Enabling ValueTracking patch by default
 (recommit). Part 2.

The original patch was an improvement to IR ValueTracking on non-negative
integers. It has been checked in to trunk (D18777, r284022). But was disabled by
default due to performance regressions.
Perf impact has improved. The patch would be enabled by default.

Reviewers: reames, hfinkel

Differential Revision: https://reviews.llvm.org/D34101

Patch by: Olga Chupina <olga.chupina@intel.com>

llvm-svn: 310583
---
 llvm/lib/Analysis/ValueTracking.cpp           |  9 -------
 .../ValueTracking/non-negative-phi-bits.ll    | 27 +++++++++++++++++++
 2 files changed, 27 insertions(+), 9 deletions(-)
 create mode 100644 llvm/test/Analysis/ValueTracking/non-negative-phi-bits.ll

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index b81bf9ec9d1a..279d880904e2 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -54,12 +54,6 @@ const unsigned MaxDepth = 6;
 static cl::opt<unsigned> DomConditionsMaxUses("dom-conditions-max-uses",
                                               cl::Hidden, cl::init(20));
 
-// This optimization is known to cause performance regressions is some cases,
-// keep it under a temporary flag for now.
-static cl::opt<bool>
-DontImproveNonNegativePhiBits("dont-improve-non-negative-phi-bits",
-                              cl::Hidden, cl::init(true));
-
 /// Returns the bitwidth of the given scalar or pointer type. For vector types,
 /// returns the element type's bitwidth.
 static unsigned getBitWidth(Type *Ty, const DataLayout &DL) {
@@ -1258,9 +1252,6 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
           Known.Zero.setLowBits(std::min(Known2.countMinTrailingZeros(),
                                          Known3.countMinTrailingZeros()));
 
-          if (DontImproveNonNegativePhiBits)
-            break;
-
           auto *OverflowOp = dyn_cast<OverflowingBinaryOperator>(LU);
           if (OverflowOp && OverflowOp->hasNoSignedWrap()) {
             // If initial value of recurrence is nonnegative, and we are adding
diff --git a/llvm/test/Analysis/ValueTracking/non-negative-phi-bits.ll b/llvm/test/Analysis/ValueTracking/non-negative-phi-bits.ll
new file mode 100644
index 000000000000..059bbaa3c4e7
--- /dev/null
+++ b/llvm/test/Analysis/ValueTracking/non-negative-phi-bits.ll
@@ -0,0 +1,27 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -instcombine < %s -S | FileCheck %s
+
+define void @test() #0 {
+; CHECK-LABEL: @test(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[INDVARS_IV_NEXT:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ult i64 [[INDVARS_IV_NEXT]], 40
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[FOR_END:%.*]], label [[FOR_BODY]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %indvars.iv.next = add nsw i64 %indvars.iv, 1
+  %exitcond = icmp slt i64 %indvars.iv.next, 40
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+  ret void
+}