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llvm-project/llvm/test/Transforms/LoopUnroll/full-unroll-one-unpredictable-exit.ll
Philip Reames de2fed6152 [unroll] Keep unrolled iterations with initial iteration 
The unrolling code was previously inserting new cloned blocks at the end of the function.  The result of this with typical loop structures is that the new iterations are placed far from the initial iteration.

With unrolling, the general assumption is that the a) the loop is reasonable hot, and b) the first Count-1 copies of the loop are rarely (if ever) loop exiting.  As such, placing Count-1 copies out of line is a fairly poor code placement choice.  We'd much rather fall through into the hot (non-exiting) path.  For code with branch profiles, later layout would fix this, but this may have a positive impact on non-PGO compiled code.

However, the real motivation for this change isn't performance.  Its readability and human understanding.  Having to jump around long distances in an IR file to trace an unrolled loop structure is error prone and tedious.
2021-11-12 11:40:50 -08:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -loop-unroll %s | FileCheck %s
; In both cases, we have one unpredictable exit and one IV-based exit with
; known trip count. We can fully unroll against the latter. In one of the
; examples the IV-based exit is the latch exit, in the other the non-latch
; exit. After full unrolling, the functions fold to ret i1 true.
define i1 @test_latch() {
; CHECK-LABEL: @test_latch(
; CHECK-NEXT: start:
; CHECK-NEXT: [[A1:%.*]] = alloca [2 x i64], align 8
; CHECK-NEXT: [[A2:%.*]] = alloca [2 x i64], align 8
; CHECK-NEXT: [[A1_0:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A1]], i64 0, i64 0
; CHECK-NEXT: store i64 -5015437470765251660, i64* [[A1_0]], align 8
; CHECK-NEXT: [[A1_1:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A1]], i64 0, i64 1
; CHECK-NEXT: store i64 -8661621401413125213, i64* [[A1_1]], align 8
; CHECK-NEXT: [[A2_0:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A2]], i64 0, i64 0
; CHECK-NEXT: store i64 -5015437470765251660, i64* [[A2_0]], align 8
; CHECK-NEXT: [[A2_1:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A2]], i64 0, i64 1
; CHECK-NEXT: store i64 -8661621401413125213, i64* [[A2_1]], align 8
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[GEP1:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A1]], i64 0, i64 0
; CHECK-NEXT: [[GEP2:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A2]], i64 0, i64 0
; CHECK-NEXT: [[LOAD1:%.*]] = load i64, i64* [[GEP1]], align 8
; CHECK-NEXT: [[LOAD2:%.*]] = load i64, i64* [[GEP2]], align 8
; CHECK-NEXT: [[EXITCOND2:%.*]] = icmp eq i64 [[LOAD1]], [[LOAD2]]
; CHECK-NEXT: br i1 [[EXITCOND2]], label [[LATCH:%.*]], label [[EXIT:%.*]]
; CHECK: latch:
; CHECK-NEXT: [[GEP1_1:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A1]], i64 0, i64 1
; CHECK-NEXT: [[GEP2_1:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A2]], i64 0, i64 1
; CHECK-NEXT: [[LOAD1_1:%.*]] = load i64, i64* [[GEP1_1]], align 8
; CHECK-NEXT: [[LOAD2_1:%.*]] = load i64, i64* [[GEP2_1]], align 8
; CHECK-NEXT: [[EXITCOND2_1:%.*]] = icmp eq i64 [[LOAD1_1]], [[LOAD2_1]]
; CHECK-NEXT: br i1 [[EXITCOND2_1]], label [[LATCH_1:%.*]], label [[EXIT]]
; CHECK: latch.1:
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: [[EXIT_VAL:%.*]] = phi i1 [ false, [[LOOP]] ], [ false, [[LATCH]] ], [ true, [[LATCH_1]] ]
; CHECK-NEXT: ret i1 [[EXIT_VAL]]
;
start:
%a1 = alloca [2 x i64], align 8
%a2 = alloca [2 x i64], align 8
%a1.0 = getelementptr inbounds [2 x i64], [2 x i64]* %a1, i64 0, i64 0
store i64 -5015437470765251660, i64* %a1.0, align 8
%a1.1 = getelementptr inbounds [2 x i64], [2 x i64]* %a1, i64 0, i64 1
store i64 -8661621401413125213, i64* %a1.1, align 8
%a2.0 = getelementptr inbounds [2 x i64], [2 x i64]* %a2, i64 0, i64 0
store i64 -5015437470765251660, i64* %a2.0, align 8
%a2.1 = getelementptr inbounds [2 x i64], [2 x i64]* %a2, i64 0, i64 1
store i64 -8661621401413125213, i64* %a2.1, align 8
br label %loop
loop:
%iv = phi i64 [ 0, %start ], [ %iv.next, %latch ]
%gep1 = getelementptr inbounds [2 x i64], [2 x i64]* %a1, i64 0, i64 %iv
%gep2 = getelementptr inbounds [2 x i64], [2 x i64]* %a2, i64 0, i64 %iv
%load1 = load i64, i64* %gep1, align 8
%load2 = load i64, i64* %gep2, align 8
%exitcond2 = icmp eq i64 %load1, %load2
br i1 %exitcond2, label %latch, label %exit
latch:
%iv.next = add nuw nsw i64 %iv, 1
%exitcond = icmp eq i64 %iv.next, 2
br i1 %exitcond, label %exit, label %loop
exit:
%exit.val = phi i1 [ true, %latch ], [ false, %loop ]
ret i1 %exit.val
}
define i1 @test_non_latch() {
; CHECK-LABEL: @test_non_latch(
; CHECK-NEXT: start:
; CHECK-NEXT: [[A1:%.*]] = alloca [2 x i64], align 8
; CHECK-NEXT: [[A2:%.*]] = alloca [2 x i64], align 8
; CHECK-NEXT: [[A1_0:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A1]], i64 0, i64 0
; CHECK-NEXT: store i64 -5015437470765251660, i64* [[A1_0]], align 8
; CHECK-NEXT: [[A1_1:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A1]], i64 0, i64 1
; CHECK-NEXT: store i64 -8661621401413125213, i64* [[A1_1]], align 8
; CHECK-NEXT: [[A2_0:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A2]], i64 0, i64 0
; CHECK-NEXT: store i64 -5015437470765251660, i64* [[A2_0]], align 8
; CHECK-NEXT: [[A2_1:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A2]], i64 0, i64 1
; CHECK-NEXT: store i64 -8661621401413125213, i64* [[A2_1]], align 8
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: br label [[LATCH:%.*]]
; CHECK: latch:
; CHECK-NEXT: [[GEP1:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A1]], i64 0, i64 0
; CHECK-NEXT: [[GEP2:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A2]], i64 0, i64 0
; CHECK-NEXT: [[LOAD1:%.*]] = load i64, i64* [[GEP1]], align 8
; CHECK-NEXT: [[LOAD2:%.*]] = load i64, i64* [[GEP2]], align 8
; CHECK-NEXT: [[EXITCOND2:%.*]] = icmp eq i64 [[LOAD1]], [[LOAD2]]
; CHECK-NEXT: br i1 [[EXITCOND2]], label [[LOOP_1:%.*]], label [[EXIT:%.*]]
; CHECK: loop.1:
; CHECK-NEXT: br label [[LATCH_1:%.*]]
; CHECK: latch.1:
; CHECK-NEXT: [[GEP1_1:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A1]], i64 0, i64 1
; CHECK-NEXT: [[GEP2_1:%.*]] = getelementptr inbounds [2 x i64], [2 x i64]* [[A2]], i64 0, i64 1
; CHECK-NEXT: [[LOAD1_1:%.*]] = load i64, i64* [[GEP1_1]], align 8
; CHECK-NEXT: [[LOAD2_1:%.*]] = load i64, i64* [[GEP2_1]], align 8
; CHECK-NEXT: [[EXITCOND2_1:%.*]] = icmp eq i64 [[LOAD1_1]], [[LOAD2_1]]
; CHECK-NEXT: br i1 [[EXITCOND2_1]], label [[LOOP_2:%.*]], label [[EXIT]]
; CHECK: loop.2:
; CHECK-NEXT: br i1 true, label [[EXIT]], label [[LATCH_2:%.*]]
; CHECK: latch.2:
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: [[EXIT_VAL:%.*]] = phi i1 [ false, [[LATCH]] ], [ false, [[LATCH_1]] ], [ true, [[LOOP_2]] ], [ false, [[LATCH_2]] ]
; CHECK-NEXT: ret i1 [[EXIT_VAL]]
;
start:
%a1 = alloca [2 x i64], align 8
%a2 = alloca [2 x i64], align 8
%a1.0 = getelementptr inbounds [2 x i64], [2 x i64]* %a1, i64 0, i64 0
store i64 -5015437470765251660, i64* %a1.0, align 8
%a1.1 = getelementptr inbounds [2 x i64], [2 x i64]* %a1, i64 0, i64 1
store i64 -8661621401413125213, i64* %a1.1, align 8
%a2.0 = getelementptr inbounds [2 x i64], [2 x i64]* %a2, i64 0, i64 0
store i64 -5015437470765251660, i64* %a2.0, align 8
%a2.1 = getelementptr inbounds [2 x i64], [2 x i64]* %a2, i64 0, i64 1
store i64 -8661621401413125213, i64* %a2.1, align 8
br label %loop
loop:
%iv = phi i64 [ 0, %start ], [ %iv.next, %latch ]
%exitcond = icmp eq i64 %iv, 2
br i1 %exitcond, label %exit, label %latch
latch:
%iv.next = add nuw nsw i64 %iv, 1
%gep1 = getelementptr inbounds [2 x i64], [2 x i64]* %a1, i64 0, i64 %iv
%gep2 = getelementptr inbounds [2 x i64], [2 x i64]* %a2, i64 0, i64 %iv
%load1 = load i64, i64* %gep1, align 8
%load2 = load i64, i64* %gep2, align 8
%exitcond2 = icmp eq i64 %load1, %load2
br i1 %exitcond2, label %loop, label %exit
exit:
%exit.val = phi i1 [ false, %latch ], [ true, %loop ]
ret i1 %exit.val
}
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