From 7e14c3da2c771da03e3d83f836aef1ad32be38e4 Mon Sep 17 00:00:00 2001
From: Serguei Katkov <serguei.katkov@azul.com>
Date: Fri, 9 Jun 2017 06:11:59 +0000
Subject: [PATCH] [IndVars] Add an option to be able to disable LFTR

This change adds an option disable-lftr to be able to disable Linear Function Test Replace optimization.
By default option is off so current behavior is not changed.

Reviewers: reames, sanjoy, wmi, andreadb, apilipenko
Reviewed By: sanjoy
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D33979


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305055 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/IndVarSimplify.cpp      |  7 ++++-
 .../IndVarSimplify/lftr_disabled.ll           | 28 +++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 test/Transforms/IndVarSimplify/lftr_disabled.ll

diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index 9a7882211ba..10782963177 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -86,6 +86,10 @@ static cl::opt<bool> UsePostIncrementRanges(
   cl::desc("Use post increment control-dependent ranges in IndVarSimplify"),
   cl::init(true));
 
+static cl::opt<bool>
+DisableLFTR("disable-lftr", cl::Hidden, cl::init(false),
+            cl::desc("Disable Linear Function Test Replace optimization"));
+
 namespace {
 struct RewritePhi;
 
@@ -2413,7 +2417,8 @@ bool IndVarSimplify::run(Loop *L) {
 
   // If we have a trip count expression, rewrite the loop's exit condition
   // using it.  We can currently only handle loops with a single exit.
-  if (canExpandBackedgeTakenCount(L, SE, Rewriter) && needsLFTR(L, DT)) {
+  if (!DisableLFTR && canExpandBackedgeTakenCount(L, SE, Rewriter) &&
+      needsLFTR(L, DT)) {
     PHINode *IndVar = FindLoopCounter(L, BackedgeTakenCount, SE, DT);
     if (IndVar) {
       // Check preconditions for proper SCEVExpander operation. SCEV does not
diff --git a/test/Transforms/IndVarSimplify/lftr_disabled.ll b/test/Transforms/IndVarSimplify/lftr_disabled.ll
new file mode 100644
index 00000000000..c647d123dd7
--- /dev/null
+++ b/test/Transforms/IndVarSimplify/lftr_disabled.ll
@@ -0,0 +1,28 @@
+; LFTR should not eliminate the need for the computation of i*i completely
+; due to LFTR is disabled.
+; RUN: opt < %s -indvars -dce -disable-lftr -S | FileCheck %s
+
+; Provide legal integer types.
+target datalayout = "n8:16:32:64"
+
+
+@A = external global i32                ; <i32*> [#uses=1]
+
+define i32 @quadratic_setlt() {
+; CHECK-LABEL: @quadratic_setlt(
+; CHECK: mul
+entry:
+        br label %loop
+
+loop:           ; preds = %loop, %entry
+        %i = phi i32 [ 7, %entry ], [ %i.next, %loop ]          ; <i32> [#uses=5]
+        %i.next = add i32 %i, 1         ; <i32> [#uses=1]
+        store i32 %i, i32* @A
+        %i2 = mul i32 %i, %i            ; <i32> [#uses=1]
+        %c = icmp slt i32 %i2, 1000             ; <i1> [#uses=1]
+        br i1 %c, label %loop, label %loopexit
+
+loopexit:               ; preds = %loop
+        ret i32 %i
+}
+