d9a4a24413
Summary: If an induction variable is frozen and used, SCEV yields imprecise result because it doesn't say anything about frozen variables. Due to this reason, performance degradation happened after https://reviews.llvm.org/D76483 is merged, causing SCEV yield imprecise result and preventing LSR to optimize a loop. The suggested solution here is to add a pass which canonicalizes frozen variables inside a loop. To be specific, it pushes freezes out of the loop by freezing the initial value and step values instead & dropping nsw/nuw flags from instructions used by freeze. This solution was also mentioned at https://reviews.llvm.org/D70623 . Reviewers: spatel, efriedma, lebedev.ri, fhahn, jdoerfert Reviewed By: fhahn Subscribers: nikic, mgorny, hiraditya, javed.absar, llvm-commits, sanwou01, nlopes Tags: #llvm Differential Revision: https://reviews.llvm.org/D77523
35 lines
1.1 KiB
LLVM
35 lines
1.1 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt < %s -canon-freeze -S | FileCheck %s
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declare void @call(i32)
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define void @add(i32 %init, i32 %n) {
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; CHECK-LABEL: @add(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: [[INIT_FROZEN:%.*]] = freeze i32 [[INIT:%.*]]
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; CHECK-NEXT: br label [[LOOP:%.*]]
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; CHECK: loop:
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; CHECK-NEXT: [[I:%.*]] = phi i32 [ [[INIT_FROZEN]], [[ENTRY:%.*]] ], [ [[I_NEXT:%.*]], [[LOOP]] ]
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; CHECK-NEXT: [[I_NEXT]] = add i32 [[I]], 1
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; CHECK-NEXT: [[NONSTEP:%.*]] = mul nsw i32 [[I]], 2
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; CHECK-NEXT: call void @call(i32 [[NONSTEP]])
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; CHECK-NEXT: [[COND:%.*]] = icmp eq i32 [[I_NEXT]], [[N:%.*]]
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; CHECK-NEXT: br i1 [[COND]], label [[LOOP]], label [[EXIT:%.*]]
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; CHECK: exit:
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; CHECK-NEXT: ret void
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;
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entry:
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br label %loop
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loop:
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%i = phi i32 [ %init, %entry], [%i.next, %loop ]
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%i.next = add nsw i32 %i, 1
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%i.next.fr = freeze i32 %i.next
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%nonstep = mul nsw i32 %i, 2
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call void @call(i32 %nonstep)
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%cond = icmp eq i32 %i.next.fr, %n
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br i1 %cond, label %loop, label %exit
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exit:
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ret void
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}
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