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