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[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

llvm-svn: 305055
This commit is contained in:
Serguei Katkov 2017-06-09 06:11:59 +00:00
parent b4b7b74b5a
commit 38414b57f9
2 changed files with 34 additions and 1 deletions
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7
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -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

28
llvm/test/Transforms/IndVarSimplify/lftr_disabled.ll Normal file
View File

@ -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
}