9f6e41cdba
This allows -polly-optree to move instructions that depend on synthesizable values. The difficulty for synthesizable values is that their value depends on the location. When it is moved over a loop header, and the SCEV expression depends on the loop induction variable (SCEVAddRecExpr), it would use the current induction variable instead of the last one. At the moment we cannot forward PHI nodes such that crossing the header of loops referenced by SCEVAddRecExpr is not possible (assuming the loop header has at least two incoming blocks: for entering the loop and the backedge, such any instruction to be forwarded must have a phi between use and definition). A remaining issue is when the forwarded value is used after the loop, but is only synthesizable inside the loop. This happens e.g. if ScalarEvolution is unable to determine the number of loop iterations or the initial loop value. We do not forward in this situation. Differential Revision: https://reviews.llvm.org/D36102 llvm-svn: 309609
51 lines
1.4 KiB
LLVM
51 lines
1.4 KiB
LLVM
; RUN: opt %loadPolly -polly-optree -analyze < %s | FileCheck %s -match-full-lines
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;
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; Do not try to forward %i.trunc, it is not synthesizable in %body.
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;
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define void @func(i32 %n, i32* noalias nonnull %A) {
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entry:
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br label %for
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for:
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%j = phi i32 [0, %entry], [%j.inc, %inc]
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%j.cmp = icmp slt i32 %j, %n
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%zero = sext i32 0 to i64
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br i1 %j.cmp, label %inner.for, label %exit
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; This loop has some unusual properties:
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; * It has a known iteration count (8), therefore SCoP-compatible.
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; * %i.trunc is synthesizable within the loop ({1,+,1}<%while.body>).
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; * %i.trunc is not synthesizable outside of the loop, because its value is
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; unknown when exiting.
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; (should be 8, but ScalarEvolution currently seems unable to derive that)
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;
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; ScalarEvolution currently seems to not able to handle the %zero.
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; If it becomes more intelligent, there might be other such loop constructs.
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inner.for:
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%i = phi i64 [%zero, %for], [%i.inc, %inner.for]
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%i.inc = add nuw nsw i64 %i, 1
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%i.trunc = trunc i64 %i.inc to i32
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%i.and = and i32 %i.trunc, 7
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%inner.cond = icmp eq i32 %i.and, 0
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br i1 %inner.cond, label %body, label %inner.for
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body:
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store i32 %i.trunc, i32* %A
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br label %inc
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inc:
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%j.inc = add nuw nsw i32 %j, 1
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br label %for
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exit:
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br label %return
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return:
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ret void
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}
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; CHECK: ForwardOpTree executed, but did not modify anything
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