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PHIElimination splits critical edges when it predicts it can resolve interference and eliminate copies. It doesn't split the edge if the interference wouldn't be resolved anyway because the phi-use register is live in the critical edge anyway. Teach PHIElimination to split loop exiting edges with interference, even if it wouldn't resolve the interference. This removes the necessary copies from the loop, which is still an improvement from injecting the copies into the loop. The test case demonstrates the improvement. Before: LBB0_1: cmpb $0, (%rdx) leaq 1(%rdx), %rdx movl %esi, %eax je LBB0_1 After: LBB0_1: cmpb $0, (%rdx) leaq 1(%rdx), %rdx je LBB0_1 movl %esi, %eax llvm-svn: 160571
31 lines
1.0 KiB
LLVM
31 lines
1.0 KiB
LLVM
; RUN: llc < %s -verify-machineinstrs | FileCheck %s
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target triple = "x86_64-apple-macosx10.8.0"
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; The critical edge from for.cond to if.end2 should be split to avoid injecting
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; copies into the loop. The use of %b after the loop causes interference that
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; makes a copy necessary.
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; <rdar://problem/11561842>
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;
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; CHECK: split_loop_exit
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; CHECK: %for.cond
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; CHECK-NOT: mov
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; CHECK: je
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define i32 @split_loop_exit(i32 %a, i32 %b, i8* nocapture %p) nounwind uwtable readonly ssp {
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entry:
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%cmp = icmp sgt i32 %a, 10
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br i1 %cmp, label %for.cond, label %if.end2
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for.cond: ; preds = %entry, %for.cond
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%p.addr.0 = phi i8* [ %incdec.ptr, %for.cond ], [ %p, %entry ]
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%incdec.ptr = getelementptr inbounds i8* %p.addr.0, i64 1
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%0 = load i8* %p.addr.0, align 1
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%tobool = icmp eq i8 %0, 0
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br i1 %tobool, label %for.cond, label %if.end2
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if.end2: ; preds = %for.cond, %entry
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%r.0 = phi i32 [ %a, %entry ], [ %b, %for.cond ]
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%add = add nsw i32 %r.0, %b
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ret i32 %add
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}
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