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LoopVectorize: Do not vectorize loops with tiny constant trip counts.

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llvm-svn: 167101
This commit is contained in:
Nadav Rotem 2012-10-31 03:31:07 +00:00
parent f4c899f8e7
commit 9ab0e93cc1
2 changed files with 41 additions and 0 deletions
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8
lib/Transforms/Vectorize/LoopVectorize.cpp
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@ -1145,6 +1145,14 @@ bool LoopVectorizationLegality::canVectorize() {
return false;
}
// Do not loop-vectorize loops with a tiny trip count.
unsigned TC = SE->getSmallConstantTripCount(TheLoop, BB);
if (TC > 0 && TC < 16) {
DEBUG(dbgs() << "LV: Found a loop with a very small trip count. " <<
"This loop is not worth vectorizing.\n");
return false;
}
DEBUG(dbgs() << "LV: We can vectorize this loop!\n");
// Okay! We can vectorize. At this point we don't have any other mem analysis

33
test/Transforms/LoopVectorize/small-loop.ll Normal file
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@ -0,0 +1,33 @@
; RUN: opt < %s -loop-vectorize -force-vector-width=4 -dce -instcombine -licm -S | FileCheck %s
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.8.0"
@a = common global [2048 x i32] zeroinitializer, align 16
@b = common global [2048 x i32] zeroinitializer, align 16
@c = common global [2048 x i32] zeroinitializer, align 16
;CHECK: @example1
;CHECK-NOT: load <4 x i32>
;CHECK: ret void
define void @example1() nounwind uwtable ssp {
br label %1
; <label>:1 ; preds = %1, %0
%indvars.iv = phi i64 [ 0, %0 ], [ %indvars.iv.next, %1 ]
%2 = getelementptr inbounds [2048 x i32]* @b, i64 0, i64 %indvars.iv
%3 = load i32* %2, align 4
%4 = getelementptr inbounds [2048 x i32]* @c, i64 0, i64 %indvars.iv
%5 = load i32* %4, align 4
%6 = add nsw i32 %5, %3
%7 = getelementptr inbounds [2048 x i32]* @a, i64 0, i64 %indvars.iv
store i32 %6, i32* %7, align 4
%indvars.iv.next = add i64 %indvars.iv, 1
%lftr.wideiv = trunc i64 %indvars.iv.next to i32
%exitcond = icmp eq i32 %lftr.wideiv, 8 ; <----- A really small trip count.
br i1 %exitcond, label %8, label %1
; <label>:8 ; preds = %1
ret void
}