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goldsteinngoldsteinn
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[InstCombine] Fold (icmp pred (trunc nuw/nsw X), C) -> (icmp pred X, (zext/sext C))
This is valid as long as the sign of the wrap flag doesn't differ from the sign of the `pred`. Proofs: https://alive2.llvm.org/ce/z/35NsrR NB: The online Alive2 hasn't been updated with `trunc nuw/nsw` support, so the proofs must be reproduced locally.
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‎llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

Lines changed: 11 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1409,6 +1409,17 @@ Instruction *InstCombinerImpl::foldICmpTruncConstant(ICmpInst &Cmp,
14091409
const APInt &C) {
14101410
ICmpInst::Predicate Pred = Cmp.getPredicate();
14111411
Value *X = Trunc->getOperand(0);
1412+
Type *SrcTy = X->getType();
1413+
unsigned DstBits = Trunc->getType()->getScalarSizeInBits(),
1414+
SrcBits = SrcTy->getScalarSizeInBits();
1415+
1416+
// Match (icmp pred (trunc nuw/nsw X), C)
1417+
// Which we can convert to (icmp pred X, (sext/zext C))
1418+
if (!Cmp.isSigned() && Trunc->hasNoUnsignedWrap())
1419+
return new ICmpInst(Pred, X, ConstantInt::get(SrcTy, C.zext(SrcBits)));
1420+
if (Trunc->hasNoSignedWrap())
1421+
return new ICmpInst(Pred, X, ConstantInt::get(SrcTy, C.sext(SrcBits)));
1422+
14121423
if (C.isOne() && C.getBitWidth() > 1) {
14131424
// icmp slt trunc(signum(V)) 1 --> icmp slt V, 1
14141425
Value *V = nullptr;
@@ -1417,10 +1428,6 @@ Instruction *InstCombinerImpl::foldICmpTruncConstant(ICmpInst &Cmp,
14171428
ConstantInt::get(V->getType(), 1));
14181429
}
14191430

1420-
Type *SrcTy = X->getType();
1421-
unsigned DstBits = Trunc->getType()->getScalarSizeInBits(),
1422-
SrcBits = SrcTy->getScalarSizeInBits();
1423-
14241431
// TODO: Handle any shifted constant by subtracting trailing zeros.
14251432
// TODO: Handle non-equality predicates.
14261433
Value *Y;

‎llvm/test/Transforms/InstCombine/cmp-intrinsic.ll

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -620,7 +620,7 @@ define i1 @trunc_cttz_false_ult_other_i32_i6_extra_use(i32 %x) {
620620
; CHECK-NEXT: [[TZ:%.*]] = tail call range(i32 0, 33) i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 false)
621621
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i32 [[TZ]] to i6
622622
; CHECK-NEXT: call void @use6(i6 [[TRUNC]])
623-
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i6 [[TRUNC]], 7
623+
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[TZ]], 7
624624
; CHECK-NEXT: ret i1 [[CMP]]
625625
;
626626
%tz = tail call i32 @llvm.cttz.i32(i32 %x, i1 false)
@@ -722,7 +722,7 @@ define i1 @trunc_ctlz_false_ugt_other_i32_i6_extra_use(i32 %x) {
722722
; CHECK-NEXT: [[LZ:%.*]] = tail call range(i32 0, 33) i32 @llvm.ctlz.i32(i32 [[X:%.*]], i1 false)
723723
; CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i32 [[LZ]] to i6
724724
; CHECK-NEXT: call void @use6(i6 [[TRUNC]])
725-
; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i6 [[TRUNC]], 4
725+
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[X]], 134217728
726726
; CHECK-NEXT: ret i1 [[CMP]]
727727
;
728728
%lz = tail call i32 @llvm.ctlz.i32(i32 %x, i1 false)

‎llvm/test/Transforms/InstCombine/icmp-trunc.ll

Lines changed: 15 additions & 32 deletions
Original file line numberDiff line numberDiff line change
@@ -557,15 +557,9 @@ define i1 @shl1_trunc_sgt4(i32 %a) {
557557
}
558558

559559
define i1 @eq_nuw(i32 %x) {
560-
; DL64-LABEL: @eq_nuw(
561-
; DL64-NEXT: [[TMP1:%.*]] = and i32 [[X:%.*]], 255
562-
; DL64-NEXT: [[R:%.*]] = icmp eq i32 [[TMP1]], 123
563-
; DL64-NEXT: ret i1 [[R]]
564-
;
565-
; DL8-LABEL: @eq_nuw(
566-
; DL8-NEXT: [[T:%.*]] = trunc nuw i32 [[X:%.*]] to i8
567-
; DL8-NEXT: [[R:%.*]] = icmp eq i8 [[T]], 123
568-
; DL8-NEXT: ret i1 [[R]]
560+
; CHECK-LABEL: @eq_nuw(
561+
; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[X:%.*]], 123
562+
; CHECK-NEXT: ret i1 [[R]]
569563
;
570564
%t = trunc nuw i32 %x to i8
571565
%r = icmp eq i8 %t, 123
@@ -574,8 +568,7 @@ define i1 @eq_nuw(i32 %x) {
574568

575569
define i1 @ult_nuw(i32 %x) {
576570
; CHECK-LABEL: @ult_nuw(
577-
; CHECK-NEXT: [[T:%.*]] = trunc nuw i32 [[X:%.*]] to i8
578-
; CHECK-NEXT: [[R:%.*]] = icmp ult i8 [[T]], 45
571+
; CHECK-NEXT: [[R:%.*]] = icmp ult i32 [[X:%.*]], 45
579572
; CHECK-NEXT: ret i1 [[R]]
580573
;
581574
%t = trunc nuw i32 %x to i8
@@ -586,7 +579,7 @@ define i1 @ult_nuw(i32 %x) {
586579
define i1 @ule_nuw(i32 %x) {
587580
; CHECK-LABEL: @ule_nuw(
588581
; CHECK-NEXT: [[T:%.*]] = trunc nuw i32 [[X:%.*]] to i8
589-
; CHECK-NEXT: [[R:%.*]] = icmp ult i8 [[T]], 46
582+
; CHECK-NEXT: [[R:%.*]] = icmp ult i32 [[X]], 46
590583
; CHECK-NEXT: call void @use(i8 [[T]])
591584
; CHECK-NEXT: ret i1 [[R]]
592585
;
@@ -598,8 +591,7 @@ define i1 @ule_nuw(i32 %x) {
598591

599592
define i1 @ugt_nuw(i32 %x) {
600593
; CHECK-LABEL: @ugt_nuw(
601-
; CHECK-NEXT: [[T:%.*]] = trunc nuw i32 [[X:%.*]] to i8
602-
; CHECK-NEXT: [[R:%.*]] = icmp ugt i8 [[T]], 12
594+
; CHECK-NEXT: [[R:%.*]] = icmp ugt i32 [[X:%.*]], 12
603595
; CHECK-NEXT: ret i1 [[R]]
604596
;
605597
%t = trunc nuw i32 %x to i8
@@ -610,7 +602,7 @@ define i1 @ugt_nuw(i32 %x) {
610602
define i1 @uge_nuw(i48 %x) {
611603
; CHECK-LABEL: @uge_nuw(
612604
; CHECK-NEXT: [[T:%.*]] = trunc nuw i48 [[X:%.*]] to i8
613-
; CHECK-NEXT: [[R:%.*]] = icmp ugt i8 [[T]], 98
605+
; CHECK-NEXT: [[R:%.*]] = icmp ugt i48 [[X]], 98
614606
; CHECK-NEXT: call void @use(i8 [[T]])
615607
; CHECK-NEXT: ret i1 [[R]]
616608
;
@@ -632,15 +624,9 @@ define i1 @sgt_nuw_fail(i32 %x) {
632624
}
633625

634626
define i1 @ne_nsw(i32 %x) {
635-
; DL64-LABEL: @ne_nsw(
636-
; DL64-NEXT: [[TMP1:%.*]] = and i32 [[X:%.*]], 255
637-
; DL64-NEXT: [[R:%.*]] = icmp ne i32 [[TMP1]], 123
638-
; DL64-NEXT: ret i1 [[R]]
639-
;
640-
; DL8-LABEL: @ne_nsw(
641-
; DL8-NEXT: [[T:%.*]] = trunc nsw i32 [[X:%.*]] to i8
642-
; DL8-NEXT: [[R:%.*]] = icmp ne i8 [[T]], 123
643-
; DL8-NEXT: ret i1 [[R]]
627+
; CHECK-LABEL: @ne_nsw(
628+
; CHECK-NEXT: [[R:%.*]] = icmp ne i32 [[X:%.*]], 123
629+
; CHECK-NEXT: ret i1 [[R]]
644630
;
645631
%t = trunc nsw i32 %x to i8
646632
%r = icmp ne i8 %t, 123
@@ -649,8 +635,7 @@ define i1 @ne_nsw(i32 %x) {
649635

650636
define i1 @slt_nsw(i32 %x) {
651637
; CHECK-LABEL: @slt_nsw(
652-
; CHECK-NEXT: [[T:%.*]] = trunc nsw i32 [[X:%.*]] to i8
653-
; CHECK-NEXT: [[R:%.*]] = icmp slt i8 [[T]], 45
638+
; CHECK-NEXT: [[R:%.*]] = icmp slt i32 [[X:%.*]], 45
654639
; CHECK-NEXT: ret i1 [[R]]
655640
;
656641
%t = trunc nsw i32 %x to i8
@@ -661,7 +646,7 @@ define i1 @slt_nsw(i32 %x) {
661646
define i1 @sle_nsw(i32 %x) {
662647
; CHECK-LABEL: @sle_nsw(
663648
; CHECK-NEXT: [[T:%.*]] = trunc nsw i32 [[X:%.*]] to i8
664-
; CHECK-NEXT: [[R:%.*]] = icmp slt i8 [[T]], 46
649+
; CHECK-NEXT: [[R:%.*]] = icmp slt i32 [[X]], 46
665650
; CHECK-NEXT: call void @use(i8 [[T]])
666651
; CHECK-NEXT: ret i1 [[R]]
667652
;
@@ -673,8 +658,7 @@ define i1 @sle_nsw(i32 %x) {
673658

674659
define i1 @sgt_nsw(i32 %x) {
675660
; CHECK-LABEL: @sgt_nsw(
676-
; CHECK-NEXT: [[T:%.*]] = trunc nsw i32 [[X:%.*]] to i8
677-
; CHECK-NEXT: [[R:%.*]] = icmp sgt i8 [[T]], 12
661+
; CHECK-NEXT: [[R:%.*]] = icmp sgt i32 [[X:%.*]], 12
678662
; CHECK-NEXT: ret i1 [[R]]
679663
;
680664
%t = trunc nsw i32 %x to i8
@@ -685,7 +669,7 @@ define i1 @sgt_nsw(i32 %x) {
685669
define i1 @sge_nsw(i48 %x) {
686670
; CHECK-LABEL: @sge_nsw(
687671
; CHECK-NEXT: [[T:%.*]] = trunc nsw i48 [[X:%.*]] to i8
688-
; CHECK-NEXT: [[R:%.*]] = icmp sgt i8 [[T]], 98
672+
; CHECK-NEXT: [[R:%.*]] = icmp sgt i48 [[X]], 98
689673
; CHECK-NEXT: call void @use(i8 [[T]])
690674
; CHECK-NEXT: ret i1 [[R]]
691675
;
@@ -698,8 +682,7 @@ define i1 @sge_nsw(i48 %x) {
698682

699683
define <2 x i1> @uge_nsw(<2 x i32> %x) {
700684
; CHECK-LABEL: @uge_nsw(
701-
; CHECK-NEXT: [[T:%.*]] = trunc nsw <2 x i32> [[X:%.*]] to <2 x i8>
702-
; CHECK-NEXT: [[R:%.*]] = icmp ugt <2 x i8> [[T]], <i8 44, i8 44>
685+
; CHECK-NEXT: [[R:%.*]] = icmp ugt <2 x i32> [[X:%.*]], <i32 44, i32 44>
703686
; CHECK-NEXT: ret <2 x i1> [[R]]
704687
;
705688
%t = trunc nsw <2 x i32> %x to <2 x i8>

‎llvm/test/Transforms/InstCombine/known-bits.ll

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -455,8 +455,7 @@ define i64 @test_icmp_trunc5(i64 %n) {
455455
; CHECK-LABEL: @test_icmp_trunc5(
456456
; CHECK-NEXT: entry:
457457
; CHECK-NEXT: [[SHR:%.*]] = ashr i64 [[N:%.*]], 47
458-
; CHECK-NEXT: [[CONV1:%.*]] = trunc nsw i64 [[SHR]] to i32
459-
; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i32 [[CONV1]], -13
458+
; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i64 [[SHR]], -13
460459
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
461460
; CHECK: if.then:
462461
; CHECK-NEXT: [[TMP0:%.*]] = and i64 [[SHR]], 15

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