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788841cb66
Summary: When simplifying unconditional branches from empty blocks, we pre-test if the BB belongs to a set of loop headers and keep the block to prevent passes from destroying canonical loop structure. However, the current algorithm fails if the destination of the branch is a loop header. Especially when such a loop's latch block is folded into loop header it results in additional backedges and LoopSimplify turns it into a nested loop which prevent later optimizations from being applied (e.g., loop unrolling and loop interleaving). This patch augments the existing algorithm by further checking if the destination of the branch belongs to a set of loop headers and defer eliminating it if yes to LateSimplifyCFG. Fixes PR33605: https://bugs.llvm.org/show_bug.cgi?id=33605 Reviewers: efriedma, mcrosier, pacxx, hsung, davidxl Reviewed By: efriedma Subscribers: ashutosh.nema, gberry, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D35411 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@308422 91177308-0d34-0410-b5e6-96231b3b80d8
40 lines
1.5 KiB
LLVM
40 lines
1.5 KiB
LLVM
; RUN: opt -latesimplifycfg -S < %s | FileCheck %s
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; It's not worthwhile to if-convert one of the phi nodes and leave
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; the other behind, because that still requires a branch. If
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; SimplifyCFG if-converts one of the phis, it should do both.
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; CHECK: %div.high.addr.0 = select i1 %cmp1, i32 %div, i32 %high.addr.0
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; CHECK-NEXT: %low.0.add2 = select i1 %cmp1, i32 %low.0, i32 %add2
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; CHECK-NEXT: br label %while.cond
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define i32 @upper_bound(i32* %r, i32 %high, i32 %k) nounwind {
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entry:
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br label %while.cond
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while.cond: ; preds = %if.then, %if.else, %entry
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%high.addr.0 = phi i32 [ %high, %entry ], [ %div, %if.then ], [ %high.addr.0, %if.else ]
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%low.0 = phi i32 [ 0, %entry ], [ %low.0, %if.then ], [ %add2, %if.else ]
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%cmp = icmp ult i32 %low.0, %high.addr.0
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br i1 %cmp, label %while.body, label %while.end
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while.body: ; preds = %while.cond
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%add = add i32 %low.0, %high.addr.0
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%div = udiv i32 %add, 2
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%idxprom = zext i32 %div to i64
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%arrayidx = getelementptr inbounds i32, i32* %r, i64 %idxprom
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%0 = load i32, i32* %arrayidx
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%cmp1 = icmp ult i32 %k, %0
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br i1 %cmp1, label %if.then, label %if.else
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if.then: ; preds = %while.body
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br label %while.cond
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if.else: ; preds = %while.body
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%add2 = add i32 %div, 1
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br label %while.cond
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while.end: ; preds = %while.cond
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ret i32 %low.0
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}
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