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llvm-project/llvm/test/Transforms/LoopUnroll/runtime-small-upperbound.ll
Justin Fargnoli cb32b8bffb [LoopUnrollPass] Don't pre-set UP.Count before legality checks in computeUnrollCount() (#185979) 
We currently set `UP.Count` to `TripCount` and `MaxTripCount` prior to
full and upper bound unrolling, respectively. This was likely done to
ensure that calls to `UCE.getUnrolledLoopSize(UP)` use the appropriate
trip count. However, we can use `UCE.getUnrolledLoopSize(UP,
FullUnrollTripCount)` instead.

To prevent unintentional unrolling, we set `UP.Count = 0` when
early-exiting `computeUnrollCount()`. (Note: this does not occur
[here](eb687fb106/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp (L1190-L1198)).
This seems like a bug.)

We only perform early exits when evaluating runtime unrolling. At that
point, [we know `TripCount` is
false](3fb31e7b06/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp (L1157-L1158)),
and thus we could not have leaked `TripCount`. However, we [could've
leaked
`MaxTripCount`](eb687fb106/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp (L1102-L1110)).

It seems like:
eb687fb106/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp (L1181-L1188)

was supposed to handle this case. However:

- It uses `<` instead of `<=`. This breaks the existing convention
[[1]](eb687fb106/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp (L869))
[[2]](eb687fb106/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp (L1103))
for how `UP.MaxUpperBound` is treated.
- It's ignored when a target sets `UP.Force = true`.

Thus:
- When `UP.Force == false`, we leak `MaxTripCount` into runtime
unrolling when `MaxTripCount && (UP.UpperBound || MaxOrZero) &&
MaxTripCount == UP.MaxUpperBound`
- When `UP.Force == true`, we leak `MaxTripCount` into runtime unrolling
when `MaxTripCount && (UP.UpperBound || MaxOrZero) && MaxTripCount <=
UP.MaxUpperBound`.

This PR:
- Uses `UCE.getUnrolledLoopSize(UP, FullUnrollTripCount)`
- Stops setting `TripCount` and `MaxTripCount` prior to calling
`shouldFullUnroll()`
- Removes the `UP.Count = 0` safeguards
- Swaps `<` with `<=`, to address the `UP.Force == false` case
- Adds a test to document the behavior change (no longer leaking
`MaxTripCount`) in the `UP.Force == true` case.
2026-03-31 19:50:52 +00:00

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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -S -passes=loop-unroll -unroll-runtime %s -o - | FileCheck %s
; RUN: opt -S -passes=loop-unroll -unroll-runtime -unroll-max-upperbound=5 %s -o - | FileCheck %s --check-prefix=UPPER
target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
@global = dso_local local_unnamed_addr global i32 0, align 4
@global.1 = dso_local local_unnamed_addr global ptr null, align 4
; Check that loop in hoge_3, with a runtime upperbound of 3, is not unrolled.
define dso_local void @hoge_3(i8 %arg) {
; CHECK-LABEL: @hoge_3(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[X:%.*]] = load i32, ptr @global, align 4
; CHECK-NEXT: [[Y:%.*]] = load ptr, ptr @global.1, align 4
; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i32 [[X]], 17
; CHECK-NEXT: br i1 [[TMP0]], label [[LOOP_PREHEADER:%.*]], label [[EXIT:%.*]]
; CHECK: loop.preheader:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ [[IV_NEXT:%.*]], [[LOOP]] ], [ [[X]], [[LOOP_PREHEADER]] ]
; CHECK-NEXT: [[PTR:%.*]] = phi ptr [ [[PTR_NEXT:%.*]], [[LOOP]] ], [ [[Y]], [[LOOP_PREHEADER]] ]
; CHECK-NEXT: [[IV_NEXT]] = add nuw i32 [[IV]], 8
; CHECK-NEXT: [[PTR_NEXT]] = getelementptr inbounds i8, ptr [[PTR]], i32 1
; CHECK-NEXT: store i8 [[ARG:%.*]], ptr [[PTR_NEXT]], align 1
; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i32 [[IV_NEXT]], 17
; CHECK-NEXT: br i1 [[TMP1]], label [[LOOP]], label [[EXIT_LOOPEXIT:%.*]]
; CHECK: exit.loopexit:
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret void
;
; UPPER-LABEL: @hoge_3(
; UPPER-NEXT: entry:
; UPPER-NEXT: [[X:%.*]] = load i32, ptr @global, align 4
; UPPER-NEXT: [[Y:%.*]] = load ptr, ptr @global.1, align 4
; UPPER-NEXT: [[TMP0:%.*]] = icmp ult i32 [[X]], 17
; UPPER-NEXT: br i1 [[TMP0]], label [[LOOP_PREHEADER:%.*]], label [[EXIT:%.*]]
; UPPER: loop.preheader:
; UPPER-NEXT: br label [[LOOP:%.*]]
; UPPER: loop:
; UPPER-NEXT: [[IV:%.*]] = phi i32 [ [[IV_NEXT:%.*]], [[LOOP]] ], [ [[X]], [[LOOP_PREHEADER]] ]
; UPPER-NEXT: [[PTR:%.*]] = phi ptr [ [[PTR_NEXT:%.*]], [[LOOP]] ], [ [[Y]], [[LOOP_PREHEADER]] ]
; UPPER-NEXT: [[IV_NEXT]] = add nuw i32 [[IV]], 8
; UPPER-NEXT: [[PTR_NEXT]] = getelementptr inbounds i8, ptr [[PTR]], i32 1
; UPPER-NEXT: store i8 [[ARG:%.*]], ptr [[PTR_NEXT]], align 1
; UPPER-NEXT: [[TMP1:%.*]] = icmp ult i32 [[IV_NEXT]], 17
; UPPER-NEXT: br i1 [[TMP1]], label [[LOOP]], label [[EXIT_LOOPEXIT:%.*]]
; UPPER: exit.loopexit:
; UPPER-NEXT: br label [[EXIT]]
; UPPER: exit:
; UPPER-NEXT: ret void
;
entry:
%x = load i32, ptr @global, align 4
%y = load ptr, ptr @global.1, align 4
%0 = icmp ult i32 %x, 17
br i1 %0, label %loop, label %exit
loop:
%iv = phi i32 [ %x, %entry ], [ %iv.next, %loop ]
%ptr = phi ptr [ %y, %entry ], [ %ptr.next, %loop ]
%iv.next = add nuw i32 %iv, 8
%ptr.next = getelementptr inbounds i8, ptr %ptr, i32 1
store i8 %arg, ptr %ptr.next, align 1
%1 = icmp ult i32 %iv.next, 17
br i1 %1, label %loop, label %exit
exit:
ret void
}
; Check that loop in hoge_5, with a runtime upperbound of 5, is unrolled when -unroll-max-upperbound=5
define dso_local void @hoge_5(i8 %arg) {
; CHECK-LABEL: @hoge_5(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[X:%.*]] = load i32, ptr @global, align 4
; CHECK-NEXT: [[Y:%.*]] = load ptr, ptr @global.1, align 4
; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i32 [[X]], 17
; CHECK-NEXT: br i1 [[TMP0]], label [[LOOP_PREHEADER:%.*]], label [[EXIT:%.*]]
; CHECK: loop.preheader:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ [[IV_NEXT:%.*]], [[LOOP]] ], [ [[X]], [[LOOP_PREHEADER]] ]
; CHECK-NEXT: [[PTR:%.*]] = phi ptr [ [[PTR_NEXT:%.*]], [[LOOP]] ], [ [[Y]], [[LOOP_PREHEADER]] ]
; CHECK-NEXT: [[IV_NEXT]] = add nuw i32 [[IV]], 4
; CHECK-NEXT: [[PTR_NEXT]] = getelementptr inbounds i8, ptr [[PTR]], i32 1
; CHECK-NEXT: store i8 [[ARG:%.*]], ptr [[PTR_NEXT]], align 1
; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i32 [[IV_NEXT]], 17
; CHECK-NEXT: br i1 [[TMP1]], label [[LOOP]], label [[EXIT_LOOPEXIT:%.*]]
; CHECK: exit.loopexit:
; CHECK-NEXT: br label [[EXIT]]
; CHECK: exit:
; CHECK-NEXT: ret void
;
; UPPER-LABEL: @hoge_5(
; UPPER-NEXT: entry:
; UPPER-NEXT: [[X:%.*]] = load i32, ptr @global, align 4
; UPPER-NEXT: [[Y:%.*]] = load ptr, ptr @global.1, align 4
; UPPER-NEXT: [[TMP0:%.*]] = icmp ult i32 [[X]], 17
; UPPER-NEXT: br i1 [[TMP0]], label [[LOOP_PREHEADER:%.*]], label [[EXIT:%.*]]
; UPPER: loop.preheader:
; UPPER-NEXT: br label [[LOOP:%.*]]
; UPPER: loop:
; UPPER-NEXT: [[IV_NEXT:%.*]] = add nuw i32 [[X]], 4
; UPPER-NEXT: [[PTR_NEXT:%.*]] = getelementptr inbounds i8, ptr [[Y]], i32 1
; UPPER-NEXT: store i8 [[ARG:%.*]], ptr [[PTR_NEXT]], align 1
; UPPER-NEXT: [[TMP1:%.*]] = icmp ult i32 [[IV_NEXT]], 17
; UPPER-NEXT: br i1 [[TMP1]], label [[LOOP_1:%.*]], label [[EXIT_LOOPEXIT:%.*]]
; UPPER: loop.1:
; UPPER-NEXT: [[IV_NEXT_1:%.*]] = add nuw i32 [[X]], 8
; UPPER-NEXT: [[PTR_NEXT_1:%.*]] = getelementptr inbounds i8, ptr [[PTR_NEXT]], i32 1
; UPPER-NEXT: store i8 [[ARG]], ptr [[PTR_NEXT_1]], align 1
; UPPER-NEXT: [[TMP2:%.*]] = icmp ult i32 [[IV_NEXT_1]], 17
; UPPER-NEXT: br i1 [[TMP2]], label [[LOOP_2:%.*]], label [[EXIT_LOOPEXIT]]
; UPPER: loop.2:
; UPPER-NEXT: [[IV_NEXT_2:%.*]] = add nuw i32 [[X]], 12
; UPPER-NEXT: [[PTR_NEXT_2:%.*]] = getelementptr inbounds i8, ptr [[PTR_NEXT_1]], i32 1
; UPPER-NEXT: store i8 [[ARG]], ptr [[PTR_NEXT_2]], align 1
; UPPER-NEXT: [[TMP3:%.*]] = icmp ult i32 [[IV_NEXT_2]], 17
; UPPER-NEXT: br i1 [[TMP3]], label [[LOOP_3:%.*]], label [[EXIT_LOOPEXIT]]
; UPPER: loop.3:
; UPPER-NEXT: [[IV_NEXT_3:%.*]] = add nuw i32 [[X]], 16
; UPPER-NEXT: [[PTR_NEXT_3:%.*]] = getelementptr inbounds i8, ptr [[PTR_NEXT_2]], i32 1
; UPPER-NEXT: store i8 [[ARG]], ptr [[PTR_NEXT_3]], align 1
; UPPER-NEXT: [[TMP4:%.*]] = icmp ult i32 [[IV_NEXT_3]], 17
; UPPER-NEXT: br i1 [[TMP4]], label [[LOOP_4:%.*]], label [[EXIT_LOOPEXIT]]
; UPPER: loop.4:
; UPPER-NEXT: [[PTR_NEXT_4:%.*]] = getelementptr inbounds i8, ptr [[PTR_NEXT_3]], i32 1
; UPPER-NEXT: store i8 [[ARG]], ptr [[PTR_NEXT_4]], align 1
; UPPER-NEXT: br i1 false, label [[LOOP_5:%.*]], label [[EXIT_LOOPEXIT]]
; UPPER: loop.5:
; UPPER-NEXT: [[PTR_NEXT_5:%.*]] = getelementptr inbounds i8, ptr [[PTR_NEXT_4]], i32 1
; UPPER-NEXT: store i8 [[ARG]], ptr [[PTR_NEXT_5]], align 1
; UPPER-NEXT: br label [[EXIT_LOOPEXIT]]
; UPPER: exit.loopexit:
; UPPER-NEXT: br label [[EXIT]]
; UPPER: exit:
; UPPER-NEXT: ret void
;
entry:
%x = load i32, ptr @global, align 4
%y = load ptr, ptr @global.1, align 4
%0 = icmp ult i32 %x, 17
br i1 %0, label %loop, label %exit
loop:
%iv = phi i32 [ %x, %entry ], [ %iv.next, %loop ]
%ptr = phi ptr [ %y, %entry ], [ %ptr.next, %loop ]
%iv.next = add nuw i32 %iv, 4
%ptr.next = getelementptr inbounds i8, ptr %ptr, i32 1
store i8 %arg, ptr %ptr.next, align 1
%1 = icmp ult i32 %iv.next, 17
br i1 %1, label %loop, label %exit
exit:
ret void
}
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