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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
65 lines
2.0 KiB
LLVM
65 lines
2.0 KiB
LLVM
; RUN: opt < %s -jump-threading -S | FileCheck %s
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; Skip simplifying unconditional branches from empty blocks in simplifyCFG,
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; when it can destroy canonical loop structure.
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; void foo();
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; bool test(int a, int b, int *c) {
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; bool changed = false;
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; for (unsigned int i = 2; i--;) {
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; int r = a | b;
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; if ( r != c[i]) {
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; c[i] = r;
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; foo();
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; changed = true;
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; }
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; }
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; return changed;
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; }
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; CHECK-LABEL: @test(
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; CHECK: for.cond:
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; CHECK-NEXT: %i.0 = phi i32 [ 2, %entry ], [ %dec, %if.end ]
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; CHECK: for.body:
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; CHECK: br i1 %cmp, label %if.end, label %if.then
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; CHECK-NOT: br i1 %cmp, label %for.cond, label %if.then
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; CHECK: if.then:
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; CHECK: br label %if.end
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; CHECK-NOT: br label %for.cond
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; CHECK: if.end:
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; CHECK br label %for.cond
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define i1 @test(i32 %a, i32 %b, i32* %c) {
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entry:
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br label %for.cond
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for.cond: ; preds = %if.end, %entry
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%i.0 = phi i32 [ 2, %entry ], [ %dec, %if.end ]
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%changed.0.off0 = phi i1 [ false, %entry ], [ %changed.1.off0, %if.end ]
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%dec = add nsw i32 %i.0, -1
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%tobool = icmp eq i32 %i.0, 0
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br i1 %tobool, label %for.cond.cleanup, label %for.body
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for.cond.cleanup: ; preds = %for.cond
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%changed.0.off0.lcssa = phi i1 [ %changed.0.off0, %for.cond ]
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ret i1 %changed.0.off0.lcssa
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for.body: ; preds = %for.cond
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%or = or i32 %a, %b
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%idxprom = sext i32 %dec to i64
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%arrayidx = getelementptr inbounds i32, i32* %c, i64 %idxprom
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%0 = load i32, i32* %arrayidx, align 4
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%cmp = icmp eq i32 %or, %0
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br i1 %cmp, label %if.end, label %if.then
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if.then: ; preds = %for.body
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store i32 %or, i32* %arrayidx, align 4
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call void @foo()
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br label %if.end
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if.end: ; preds = %for.body, %if.then
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%changed.1.off0 = phi i1 [ true, %if.then ], [ %changed.0.off0, %for.body ]
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br label %for.cond
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}
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declare void @foo()
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