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FIXME: or when the offset was "add nuw" #130451

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3799bfb
Pre-commit tests [NFC]
AZero13 Mar 9, 2025
a950fba
FIXME: or when the offset was `add nuw`
AZero13 Mar 9, 2025
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8 changes: 6 additions & 2 deletions llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3020,10 +3020,14 @@ bool LoopIdiomRecognize::recognizeShiftUntilZero() {
{ValNumActiveBitsOffset, Start},
/*FMFSource=*/nullptr, "iv.final");

// Check if the offset was added with NUW flag
bool OffsetAddHasNUW = OffsetIsZero;
if (auto *OffsetAddInst = dyn_cast<BinaryOperator>(ValNumActiveBitsOffset))
OffsetAddHasNUW |= OffsetAddInst->hasNoUnsignedWrap();

auto *LoopBackedgeTakenCount = cast<Instruction>(Builder.CreateSub(
IVFinal, Start, CurLoop->getName() + ".backedgetakencount",
/*HasNUW=*/OffsetIsZero, /*HasNSW=*/true));
// FIXME: or when the offset was `add nuw`
/*HasNUW=*/OffsetAddHasNUW, /*HasNSW=*/true));

// We know loop's backedge-taken count, but what's loop's trip count?
Value *LoopTripCount =
Expand Down
227 changes: 227 additions & 0 deletions llvm/test/Transforms/LoopIdiom/X86/preserve-nuw-flag-shift-until-zero.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,227 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt -passes=loop-idiom -mtriple=x86_64 -mcpu=core-avx2 < %s -S | FileCheck %s

declare void @escape_inner(i8, i8, i8, i1, i8)
declare void @escape_outer(i8, i8, i8, i1, i8)

; Test cases where the offset addition has the nuw flag and this property
; should be preserved in the backedge taken count calculation.

; Basic case: add nuw - check that HasNUW is preserved
define i8 @preserve_nuw_flag(i8 %val, i8 %start, i8 %extraoffset) {
; CHECK-LABEL: @preserve_nuw_flag(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[VAL_NUMLEADINGZEROS:%.*]] = call i8 @llvm.ctlz.i8(i8 [[VAL:%.*]], i1 false)
; CHECK-NEXT: [[VAL_NUMACTIVEBITS:%.*]] = sub nuw nsw i8 8, [[VAL_NUMLEADINGZEROS]]
; CHECK-NEXT: [[TMP0:%.*]] = sub i8 0, [[EXTRAOFFSET:%.*]]
; CHECK-NEXT: [[VAL_NUMACTIVEBITS_OFFSET:%.*]] = add nsw i8 [[VAL_NUMACTIVEBITS]], [[TMP0]]
; CHECK-NEXT: [[IV_FINAL:%.*]] = call i8 @llvm.smax.i8(i8 [[VAL_NUMACTIVEBITS_OFFSET]], i8 [[START:%.*]])
; CHECK-NEXT: [[LOOP_BACKEDGETAKENCOUNT:%.*]] = sub nsw i8 [[IV_FINAL]], [[START]]
; CHECK-NEXT: [[LOOP_TRIPCOUNT:%.*]] = add nuw nsw i8 [[LOOP_BACKEDGETAKENCOUNT]], 1
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[LOOP_IV:%.*]] = phi i8 [ 0, [[ENTRY:%.*]] ], [ [[LOOP_IV_NEXT:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[LOOP_IV_NEXT]] = add nuw nsw i8 [[LOOP_IV]], 1
; CHECK-NEXT: [[LOOP_IVCHECK:%.*]] = icmp eq i8 [[LOOP_IV_NEXT]], [[LOOP_TRIPCOUNT]]
; CHECK-NEXT: [[IV:%.*]] = add nsw i8 [[LOOP_IV]], [[START]]
; CHECK-NEXT: [[NBITS:%.*]] = add nuw i8 [[IV]], [[EXTRAOFFSET]]
; CHECK-NEXT: [[VAL_SHIFTED:%.*]] = lshr i8 [[VAL]], [[NBITS]]
; CHECK-NEXT: [[IV_NEXT:%.*]] = add i8 [[IV]], 1
; CHECK-NEXT: call void @escape_inner(i8 [[IV]], i8 [[NBITS]], i8 [[VAL_SHIFTED]], i1 [[LOOP_IVCHECK]], i8 [[IV_NEXT]])
; CHECK-NEXT: br i1 [[LOOP_IVCHECK]], label [[END:%.*]], label [[LOOP]]
; CHECK: end:
; CHECK-NEXT: [[IV_RES:%.*]] = phi i8 [ [[IV_FINAL]], [[LOOP]] ]
; CHECK-NEXT: [[NBITS_RES:%.*]] = phi i8 [ [[NBITS]], [[LOOP]] ]
; CHECK-NEXT: [[VAL_SHIFTED_RES:%.*]] = phi i8 [ [[VAL_SHIFTED]], [[LOOP]] ]
; CHECK-NEXT: [[VAL_SHIFTED_ISZERO_RES:%.*]] = phi i1 [ [[LOOP_IVCHECK]], [[LOOP]] ]
; CHECK-NEXT: [[IV_NEXT_RES:%.*]] = phi i8 [ [[IV_NEXT]], [[LOOP]] ]
; CHECK-NEXT: call void @escape_outer(i8 [[IV_RES]], i8 [[NBITS_RES]], i8 [[VAL_SHIFTED_RES]], i1 [[VAL_SHIFTED_ISZERO_RES]], i8 [[IV_NEXT_RES]])
; CHECK-NEXT: ret i8 [[IV_RES]]
;
entry:
br label %loop

loop:
%iv = phi i8 [ %start, %entry ], [ %iv.next, %loop ]
%nbits = add nuw i8 %iv, %extraoffset
%val.shifted = lshr i8 %val, %nbits
%val.shifted.iszero = icmp eq i8 %val.shifted, 0
%iv.next = add i8 %iv, 1

call void @escape_inner(i8 %iv, i8 %nbits, i8 %val.shifted, i1 %val.shifted.iszero, i8 %iv.next)

br i1 %val.shifted.iszero, label %end, label %loop

end:
%iv.res = phi i8 [ %iv, %loop ]
%nbits.res = phi i8 [ %nbits, %loop ]
%val.shifted.res = phi i8 [ %val.shifted, %loop ]
%val.shifted.iszero.res = phi i1 [ %val.shifted.iszero, %loop ]
%iv.next.res = phi i8 [ %iv.next, %loop ]

call void @escape_outer(i8 %iv.res, i8 %nbits.res, i8 %val.shifted.res, i1 %val.shifted.iszero.res, i8 %iv.next.res)

ret i8 %iv.res
}

; Test with both nuw and nsw flags on the offset addition
define i8 @preserve_nuw_nsw_flags(i8 %val, i8 %start, i8 %extraoffset) {
; CHECK-LABEL: @preserve_nuw_nsw_flags(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[VAL_NUMLEADINGZEROS:%.*]] = call i8 @llvm.ctlz.i8(i8 [[VAL:%.*]], i1 false)
; CHECK-NEXT: [[VAL_NUMACTIVEBITS:%.*]] = sub nuw nsw i8 8, [[VAL_NUMLEADINGZEROS]]
; CHECK-NEXT: [[TMP0:%.*]] = sub i8 0, [[EXTRAOFFSET:%.*]]
; CHECK-NEXT: [[VAL_NUMACTIVEBITS_OFFSET:%.*]] = add nsw i8 [[VAL_NUMACTIVEBITS]], [[TMP0]]
; CHECK-NEXT: [[IV_FINAL:%.*]] = call i8 @llvm.smax.i8(i8 [[VAL_NUMACTIVEBITS_OFFSET]], i8 [[START:%.*]])
; CHECK-NEXT: [[LOOP_BACKEDGETAKENCOUNT:%.*]] = sub nsw i8 [[IV_FINAL]], [[START]]
; CHECK-NEXT: [[LOOP_TRIPCOUNT:%.*]] = add nuw nsw i8 [[LOOP_BACKEDGETAKENCOUNT]], 1
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[LOOP_IV:%.*]] = phi i8 [ 0, [[ENTRY:%.*]] ], [ [[LOOP_IV_NEXT:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[LOOP_IV_NEXT]] = add nuw nsw i8 [[LOOP_IV]], 1
; CHECK-NEXT: [[LOOP_IVCHECK:%.*]] = icmp eq i8 [[LOOP_IV_NEXT]], [[LOOP_TRIPCOUNT]]
; CHECK-NEXT: [[IV:%.*]] = add nsw i8 [[LOOP_IV]], [[START]]
; CHECK-NEXT: [[NBITS:%.*]] = add nuw nsw i8 [[IV]], [[EXTRAOFFSET]]
; CHECK-NEXT: [[VAL_SHIFTED:%.*]] = lshr i8 [[VAL]], [[NBITS]]
; CHECK-NEXT: [[IV_NEXT:%.*]] = add i8 [[IV]], 1
; CHECK-NEXT: call void @escape_inner(i8 [[IV]], i8 [[NBITS]], i8 [[VAL_SHIFTED]], i1 [[LOOP_IVCHECK]], i8 [[IV_NEXT]])
; CHECK-NEXT: br i1 [[LOOP_IVCHECK]], label [[END:%.*]], label [[LOOP]]
; CHECK: end:
; CHECK-NEXT: [[IV_RES:%.*]] = phi i8 [ [[IV_FINAL]], [[LOOP]] ]
; CHECK-NEXT: [[NBITS_RES:%.*]] = phi i8 [ [[NBITS]], [[LOOP]] ]
; CHECK-NEXT: [[VAL_SHIFTED_RES:%.*]] = phi i8 [ [[VAL_SHIFTED]], [[LOOP]] ]
; CHECK-NEXT: [[VAL_SHIFTED_ISZERO_RES:%.*]] = phi i1 [ [[LOOP_IVCHECK]], [[LOOP]] ]
; CHECK-NEXT: [[IV_NEXT_RES:%.*]] = phi i8 [ [[IV_NEXT]], [[LOOP]] ]
; CHECK-NEXT: call void @escape_outer(i8 [[IV_RES]], i8 [[NBITS_RES]], i8 [[VAL_SHIFTED_RES]], i1 [[VAL_SHIFTED_ISZERO_RES]], i8 [[IV_NEXT_RES]])
; CHECK-NEXT: ret i8 [[IV_RES]]
;
entry:
br label %loop

loop:
%iv = phi i8 [ %start, %entry ], [ %iv.next, %loop ]
%nbits = add nuw nsw i8 %iv, %extraoffset
%val.shifted = lshr i8 %val, %nbits
%val.shifted.iszero = icmp eq i8 %val.shifted, 0
%iv.next = add i8 %iv, 1

call void @escape_inner(i8 %iv, i8 %nbits, i8 %val.shifted, i1 %val.shifted.iszero, i8 %iv.next)

br i1 %val.shifted.iszero, label %end, label %loop

end:
%iv.res = phi i8 [ %iv, %loop ]
%nbits.res = phi i8 [ %nbits, %loop ]
%val.shifted.res = phi i8 [ %val.shifted, %loop ]
%val.shifted.iszero.res = phi i1 [ %val.shifted.iszero, %loop ]
%iv.next.res = phi i8 [ %iv.next, %loop ]

call void @escape_outer(i8 %iv.res, i8 %nbits.res, i8 %val.shifted.res, i1 %val.shifted.iszero.res, i8 %iv.next.res)

ret i8 %iv.res
}

; Test with left shift instead of logical right shift
define i8 @preserve_nuw_flag_shl(i8 %val, i8 %start, i8 %extraoffset) {
; CHECK-LABEL: @preserve_nuw_flag_shl(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[VAL_NUMLEADINGZEROS:%.*]] = call i8 @llvm.cttz.i8(i8 [[VAL:%.*]], i1 false)
; CHECK-NEXT: [[VAL_NUMACTIVEBITS:%.*]] = sub nuw nsw i8 8, [[VAL_NUMLEADINGZEROS]]
; CHECK-NEXT: [[TMP0:%.*]] = sub i8 0, [[EXTRAOFFSET:%.*]]
; CHECK-NEXT: [[VAL_NUMACTIVEBITS_OFFSET:%.*]] = add nsw i8 [[VAL_NUMACTIVEBITS]], [[TMP0]]
; CHECK-NEXT: [[IV_FINAL:%.*]] = call i8 @llvm.smax.i8(i8 [[VAL_NUMACTIVEBITS_OFFSET]], i8 [[START:%.*]])
; CHECK-NEXT: [[LOOP_BACKEDGETAKENCOUNT:%.*]] = sub nsw i8 [[IV_FINAL]], [[START]]
; CHECK-NEXT: [[LOOP_TRIPCOUNT:%.*]] = add nuw nsw i8 [[LOOP_BACKEDGETAKENCOUNT]], 1
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[LOOP_IV:%.*]] = phi i8 [ 0, [[ENTRY:%.*]] ], [ [[LOOP_IV_NEXT:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[LOOP_IV_NEXT]] = add nuw nsw i8 [[LOOP_IV]], 1
; CHECK-NEXT: [[LOOP_IVCHECK:%.*]] = icmp eq i8 [[LOOP_IV_NEXT]], [[LOOP_TRIPCOUNT]]
; CHECK-NEXT: [[IV:%.*]] = add nsw i8 [[LOOP_IV]], [[START]]
; CHECK-NEXT: [[NBITS:%.*]] = add nuw i8 [[IV]], [[EXTRAOFFSET]]
; CHECK-NEXT: [[VAL_SHIFTED:%.*]] = shl i8 [[VAL]], [[NBITS]]
; CHECK-NEXT: [[IV_NEXT:%.*]] = add i8 [[IV]], 1
; CHECK-NEXT: call void @escape_inner(i8 [[IV]], i8 [[NBITS]], i8 [[VAL_SHIFTED]], i1 [[LOOP_IVCHECK]], i8 [[IV_NEXT]])
; CHECK-NEXT: br i1 [[LOOP_IVCHECK]], label [[END:%.*]], label [[LOOP]]
; CHECK: end:
; CHECK-NEXT: [[IV_RES:%.*]] = phi i8 [ [[IV_FINAL]], [[LOOP]] ]
; CHECK-NEXT: [[NBITS_RES:%.*]] = phi i8 [ [[NBITS]], [[LOOP]] ]
; CHECK-NEXT: [[VAL_SHIFTED_RES:%.*]] = phi i8 [ [[VAL_SHIFTED]], [[LOOP]] ]
; CHECK-NEXT: [[VAL_SHIFTED_ISZERO_RES:%.*]] = phi i1 [ [[LOOP_IVCHECK]], [[LOOP]] ]
; CHECK-NEXT: [[IV_NEXT_RES:%.*]] = phi i8 [ [[IV_NEXT]], [[LOOP]] ]
; CHECK-NEXT: call void @escape_outer(i8 [[IV_RES]], i8 [[NBITS_RES]], i8 [[VAL_SHIFTED_RES]], i1 [[VAL_SHIFTED_ISZERO_RES]], i8 [[IV_NEXT_RES]])
; CHECK-NEXT: ret i8 [[IV_RES]]
;
entry:
br label %loop

loop:
%iv = phi i8 [ %start, %entry ], [ %iv.next, %loop ]
%nbits = add nuw i8 %iv, %extraoffset
%val.shifted = shl i8 %val, %nbits
%val.shifted.iszero = icmp eq i8 %val.shifted, 0
%iv.next = add i8 %iv, 1

call void @escape_inner(i8 %iv, i8 %nbits, i8 %val.shifted, i1 %val.shifted.iszero, i8 %iv.next)

br i1 %val.shifted.iszero, label %end, label %loop

end:
%iv.res = phi i8 [ %iv, %loop ]
%nbits.res = phi i8 [ %nbits, %loop ]
%val.shifted.res = phi i8 [ %val.shifted, %loop ]
%val.shifted.iszero.res = phi i1 [ %val.shifted.iszero, %loop ]
%iv.next.res = phi i8 [ %iv.next, %loop ]

call void @escape_outer(i8 %iv.res, i8 %nbits.res, i8 %val.shifted.res, i1 %val.shifted.iszero.res, i8 %iv.next.res)

ret i8 %iv.res
}

; Test with arithmetic right shift
define i8 @preserve_nuw_flag_ashr(i8 %val, i8 %start, i8 %extraoffset) {
; CHECK-LABEL: @preserve_nuw_flag_ashr(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i8 [ [[START:%.*]], [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[NBITS:%.*]] = add nuw i8 [[IV]], [[EXTRAOFFSET:%.*]]
; CHECK-NEXT: [[VAL_SHIFTED:%.*]] = ashr i8 [[VAL:%.*]], [[NBITS]]
; CHECK-NEXT: [[VAL_SHIFTED_ISZERO:%.*]] = icmp eq i8 [[VAL_SHIFTED]], 0
; CHECK-NEXT: [[IV_NEXT]] = add i8 [[IV]], 1
; CHECK-NEXT: call void @escape_inner(i8 [[IV]], i8 [[NBITS]], i8 [[VAL_SHIFTED]], i1 [[VAL_SHIFTED_ISZERO]], i8 [[IV_NEXT]])
; CHECK-NEXT: br i1 [[VAL_SHIFTED_ISZERO]], label [[END:%.*]], label [[LOOP]]
; CHECK: end:
; CHECK-NEXT: [[IV_RES:%.*]] = phi i8 [ [[IV]], [[LOOP]] ]
; CHECK-NEXT: [[NBITS_RES:%.*]] = phi i8 [ [[NBITS]], [[LOOP]] ]
; CHECK-NEXT: [[VAL_SHIFTED_RES:%.*]] = phi i8 [ [[VAL_SHIFTED]], [[LOOP]] ]
; CHECK-NEXT: [[VAL_SHIFTED_ISZERO_RES:%.*]] = phi i1 [ [[VAL_SHIFTED_ISZERO]], [[LOOP]] ]
; CHECK-NEXT: [[IV_NEXT_RES:%.*]] = phi i8 [ [[IV_NEXT]], [[LOOP]] ]
; CHECK-NEXT: call void @escape_outer(i8 [[IV_RES]], i8 [[NBITS_RES]], i8 [[VAL_SHIFTED_RES]], i1 [[VAL_SHIFTED_ISZERO_RES]], i8 [[IV_NEXT_RES]])
; CHECK-NEXT: ret i8 [[IV_RES]]
;
entry:
br label %loop

loop:
%iv = phi i8 [ %start, %entry ], [ %iv.next, %loop ]
%nbits = add nuw i8 %iv, %extraoffset
%val.shifted = ashr i8 %val, %nbits
%val.shifted.iszero = icmp eq i8 %val.shifted, 0
%iv.next = add i8 %iv, 1

call void @escape_inner(i8 %iv, i8 %nbits, i8 %val.shifted, i1 %val.shifted.iszero, i8 %iv.next)

br i1 %val.shifted.iszero, label %end, label %loop

end:
%iv.res = phi i8 [ %iv, %loop ]
%nbits.res = phi i8 [ %nbits, %loop ]
%val.shifted.res = phi i8 [ %val.shifted, %loop ]
%val.shifted.iszero.res = phi i1 [ %val.shifted.iszero, %loop ]
%iv.next.res = phi i8 [ %iv.next, %loop ]

call void @escape_outer(i8 %iv.res, i8 %nbits.res, i8 %val.shifted.res, i1 %val.shifted.iszero.res, i8 %iv.next.res)

ret i8 %iv.res
}