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llvm-mirror/test/Transforms/LoopUnroll/full-unroll-keep-first-exit.ll
John Brawn c944a4af03 [LoopUnroll] Keep the loop test only on the first iteration of max-or-zero loops 
When we have a loop with a known upper bound on the number of iterations, and
furthermore know that either the number of iterations will be either exactly
that upper bound or zero, then we can fully unroll up to that upper bound
keeping only the first loop test to check for the zero iteration case.

Most of the work here is in plumbing this 'max-or-zero' information from the
part of scalar evolution where it's detected through to loop unrolling. I've
also gone for the safe default of 'false' everywhere but howManyLessThans which
could probably be improved.

Differential Revision: https://reviews.llvm.org/D25682

llvm-svn: 284818
2016-10-21 11:08:48 +00:00

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; RUN: opt -S -loop-unroll < %s | FileCheck %s
; Unroll twice, with first loop exit kept
; CHECK-LABEL: @s32_max1
; CHECK: do.body:
; CHECK: store
; CHECK: br i1 %cmp, label %do.body.1, label %do.end
; CHECK: do.end:
; CHECK: ret void
; CHECK: do.body.1:
; CHECK: store
; CHECK: br label %do.end
define void @s32_max1(i32 %n, i32* %p) {
entry:
%add = add i32 %n, 1
br label %do.body
do.body:
%i.0 = phi i32 [ %n, %entry ], [ %inc, %do.body ]
%arrayidx = getelementptr i32, i32* %p, i32 %i.0
store i32 %i.0, i32* %arrayidx, align 4
%inc = add i32 %i.0, 1
%cmp = icmp slt i32 %i.0, %add
br i1 %cmp, label %do.body, label %do.end ; taken either 0 or 1 times
do.end:
ret void
}
; Unroll thrice, with first loop exit kept
; CHECK-LABEL: @s32_max2
; CHECK: do.body:
; CHECK: store
; CHECK: br i1 %cmp, label %do.body.1, label %do.end
; CHECK: do.end:
; CHECK: ret void
; CHECK: do.body.1:
; CHECK: store
; CHECK: store
; CHECK: br label %do.end
define void @s32_max2(i32 %n, i32* %p) {
entry:
%add = add i32 %n, 2
br label %do.body
do.body:
%i.0 = phi i32 [ %n, %entry ], [ %inc, %do.body ]
%arrayidx = getelementptr i32, i32* %p, i32 %i.0
store i32 %i.0, i32* %arrayidx, align 4
%inc = add i32 %i.0, 1
%cmp = icmp slt i32 %i.0, %add
br i1 %cmp, label %do.body, label %do.end ; taken either 0 or 2 times
do.end:
ret void
}
; Should not be unrolled
; CHECK-LABEL: @s32_maxx
; CHECK: do.body:
; CHECK: do.end:
; CHECK-NOT: do.body.1:
define void @s32_maxx(i32 %n, i32 %x, i32* %p) {
entry:
%add = add i32 %x, %n
br label %do.body
do.body:
%i.0 = phi i32 [ %n, %entry ], [ %inc, %do.body ]
%arrayidx = getelementptr i32, i32* %p, i32 %i.0
store i32 %i.0, i32* %arrayidx, align 4
%inc = add i32 %i.0, 1
%cmp = icmp slt i32 %i.0, %add
br i1 %cmp, label %do.body, label %do.end ; taken either 0 or x times
do.end:
ret void
}
; Should not be unrolled
; CHECK-LABEL: @s32_max2_unpredictable_exit
; CHECK: do.body:
; CHECK: do.end:
; CHECK-NOT: do.body.1:
define void @s32_max2_unpredictable_exit(i32 %n, i32 %x, i32* %p) {
entry:
%add = add i32 %n, 2
br label %do.body
do.body:
%i.0 = phi i32 [ %n, %entry ], [ %inc, %if.end ]
%cmp = icmp eq i32 %i.0, %x
br i1 %cmp, label %do.end, label %if.end ; unpredictable
if.end:
%arrayidx = getelementptr i32, i32* %p, i32 %i.0
store i32 %i.0, i32* %arrayidx, align 4
%inc = add i32 %i.0, 1
%cmp1 = icmp slt i32 %i.0, %add
br i1 %cmp1, label %do.body, label %do.end ; taken either 0 or 2 times
do.end:
ret void
}
; Unroll twice, with first loop exit kept
; CHECK-LABEL: @u32_max1
; CHECK: do.body:
; CHECK: store
; CHECK: br i1 %cmp, label %do.body.1, label %do.end
; CHECK: do.end:
; CHECK: ret void
; CHECK: do.body.1:
; CHECK: store
; CHECK: br label %do.end
define void @u32_max1(i32 %n, i32* %p) {
entry:
%add = add i32 %n, 1
br label %do.body
do.body:
%i.0 = phi i32 [ %n, %entry ], [ %inc, %do.body ]
%arrayidx = getelementptr i32, i32* %p, i32 %i.0
store i32 %i.0, i32* %arrayidx, align 4
%inc = add i32 %i.0, 1
%cmp = icmp ult i32 %i.0, %add
br i1 %cmp, label %do.body, label %do.end ; taken either 0 or 1 times
do.end:
ret void
}
; Unroll thrice, with first loop exit kept
; CHECK-LABEL: @u32_max2
; CHECK: do.body:
; CHECK: store
; CHECK: br i1 %cmp, label %do.body.1, label %do.end
; CHECK: do.end:
; CHECK: ret void
; CHECK: do.body.1:
; CHECK: store
; CHECK: store
; CHECK: br label %do.end
define void @u32_max2(i32 %n, i32* %p) {
entry:
%add = add i32 %n, 2
br label %do.body
do.body:
%i.0 = phi i32 [ %n, %entry ], [ %inc, %do.body ]
%arrayidx = getelementptr i32, i32* %p, i32 %i.0
store i32 %i.0, i32* %arrayidx, align 4
%inc = add i32 %i.0, 1
%cmp = icmp ult i32 %i.0, %add
br i1 %cmp, label %do.body, label %do.end ; taken either 0 or 2 times
do.end:
ret void
}
; Should not be unrolled
; CHECK-LABEL: @u32_maxx
; CHECK: do.body:
; CHECK: do.end:
; CHECK-NOT: do.body.1:
define void @u32_maxx(i32 %n, i32 %x, i32* %p) {
entry:
%add = add i32 %x, %n
br label %do.body
do.body:
%i.0 = phi i32 [ %n, %entry ], [ %inc, %do.body ]
%arrayidx = getelementptr i32, i32* %p, i32 %i.0
store i32 %i.0, i32* %arrayidx, align 4
%inc = add i32 %i.0, 1
%cmp = icmp ult i32 %i.0, %add
br i1 %cmp, label %do.body, label %do.end ; taken either 0 or x times
do.end:
ret void
}
; Should not be unrolled
; CHECK-LABEL: @u32_max2_unpredictable_exit
; CHECK: do.body:
; CHECK: do.end:
; CHECK-NOT: do.body.1:
define void @u32_max2_unpredictable_exit(i32 %n, i32 %x, i32* %p) {
entry:
%add = add i32 %n, 2
br label %do.body
do.body:
%i.0 = phi i32 [ %n, %entry ], [ %inc, %if.end ]
%cmp = icmp eq i32 %i.0, %x
br i1 %cmp, label %do.end, label %if.end ; unpredictable
if.end:
%arrayidx = getelementptr i32, i32* %p, i32 %i.0
store i32 %i.0, i32* %arrayidx, align 4
%inc = add i32 %i.0, 1
%cmp1 = icmp ult i32 %i.0, %add
br i1 %cmp1, label %do.body, label %do.end ; taken either 0 or 2 times
do.end:
ret void
}
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