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a04c210c0a
This addresses a vectorisation regression for tail-folded loops that are
counting down, e.g. loops as simple as this:
void foo(char *A, char *B, char *C, uint32_t N) {
while (N > 0) {
*C++ = *A++ + *B++;
N--;
}
}
These are loops that can be vectorised, but when tail-folding is requested, it
can't find a primary induction variable which we do need for predicating the
loop. As a result, the loop isn't vectorised at all, which it is able to do
when tail-folding is not attempted. So, this adds a check for the primary
induction variable where we decide how to lower the scalar epilogue. I.e., when
there isn't a primary induction variable, a scalar epilogue loop is allowed
(i.e. don't request tail-folding) so that vectorisation could still be
triggered.
Having this check for the primary induction variable make sense anyway, and in
addition, in a follow-up of this I will look into discovering earlier the
primary induction variable for counting down loops, so that this can also be
tail-folded.
Differential revision: https://reviews.llvm.org/D72324
43 lines
1.6 KiB
LLVM
43 lines
1.6 KiB
LLVM
; RUN: opt < %s -loop-vectorize -prefer-predicate-over-epilog -S | FileCheck %s
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; Check that when we can't predicate this loop that it is still vectorised (with
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; an epilogue).
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; TODO: the reason this can't be predicated is because a primary induction
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; variable can't be found (not yet) for this counting down loop. But with that
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; fixed, this should be able to be predicated.
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; CHECK-LABEL: vector.body:
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target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
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define dso_local void @foo(i8* noalias nocapture readonly %A, i8* noalias nocapture readonly %B, i8* noalias nocapture %C, i32 %N) {
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entry:
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%cmp6 = icmp eq i32 %N, 0
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br i1 %cmp6, label %while.end, label %while.body.preheader
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while.body.preheader:
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br label %while.body
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while.body:
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%N.addr.010 = phi i32 [ %dec, %while.body ], [ %N, %while.body.preheader ]
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%C.addr.09 = phi i8* [ %incdec.ptr4, %while.body ], [ %C, %while.body.preheader ]
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%B.addr.08 = phi i8* [ %incdec.ptr1, %while.body ], [ %B, %while.body.preheader ]
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%A.addr.07 = phi i8* [ %incdec.ptr, %while.body ], [ %A, %while.body.preheader ]
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%incdec.ptr = getelementptr inbounds i8, i8* %A.addr.07, i32 1
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%0 = load i8, i8* %A.addr.07, align 1
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%incdec.ptr1 = getelementptr inbounds i8, i8* %B.addr.08, i32 1
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%1 = load i8, i8* %B.addr.08, align 1
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%add = add i8 %1, %0
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%incdec.ptr4 = getelementptr inbounds i8, i8* %C.addr.09, i32 1
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store i8 %add, i8* %C.addr.09, align 1
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%dec = add i32 %N.addr.010, -1
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%cmp = icmp eq i32 %dec, 0
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br i1 %cmp, label %while.end.loopexit, label %while.body
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while.end.loopexit:
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br label %while.end
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while.end:
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ret void
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}
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