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[SCEV] Add predicate in SolveLinEq to ensure B is a multiple of A. #108777

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Merged
merged 10 commits into from
Sep 28, 2024
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[SCEV] Add predicate in SolveLinEq to ensure B is a multiple of A. #108777

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c91b942
[SCEV] Add predicate in SolveLinEq to ensure B is a multiple of A.
fhahn Sep 15, 2024
2832a8a
Merge remote-tracking branch 'origin/main' into scev-align-predicate
fhahn Sep 26, 2024
fcf36c4
!fixup Address latest comments, thanks!
fhahn Sep 26, 2024
f23bddc
Merge remote-tracking branch 'origin/main' into scev-align-predicate
fhahn Sep 26, 2024
c312060
!fixup update and assert.
fhahn Sep 26, 2024
d6522f9
!fixup use APInt::getOneBitSet, thanks!
fhahn Sep 26, 2024
7624c7d
Merge remote-tracking branch 'origin/main' into scev-align-predicate
fhahn Sep 27, 2024
f648176
Merge remote-tracking branch 'origin/main' into scev-align-predicate
fhahn Sep 27, 2024
e36de7d
!fixup replace assertion with check
fhahn Sep 27, 2024
ee755af
!fixup update thumb test
fhahn Sep 28, 2024
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28 changes: 22 additions & 6 deletions llvm/lib/Analysis/ScalarEvolution.cpp
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Expand Up @@ -10129,8 +10129,11 @@ const SCEV *ScalarEvolution::stripInjectiveFunctions(const SCEV *S) const {
/// A and B isn't important.
///
/// If the equation does not have a solution, SCEVCouldNotCompute is returned.
static const SCEV *SolveLinEquationWithOverflow(const APInt &A, const SCEV *B,
ScalarEvolution &SE) {
static const SCEV *
SolveLinEquationWithOverflow(const APInt &A, const SCEV *B,
SmallPtrSetImpl<const SCEVPredicate *> *Predicates,

ScalarEvolution &SE) {
uint32_t BW = A.getBitWidth();
assert(BW == SE.getTypeSizeInBits(B->getType()));
assert(A != 0 && "A must be non-zero.");
Expand All @@ -10146,8 +10149,20 @@ static const SCEV *SolveLinEquationWithOverflow(const APInt &A, const SCEV *B,
//
// B is divisible by D if and only if the multiplicity of prime factor 2 for B
// is not less than multiplicity of this prime factor for D.
if (SE.getMinTrailingZeros(B) < Mult2)
return SE.getCouldNotCompute();
if (SE.getMinTrailingZeros(B) < Mult2) {
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@preames preames Sep 17, 2024

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Should we maybe try to prove that (urem B, A) == 0 before resorting to the predicate?

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@fhahn fhahn Sep 26, 2024

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IIUC that check shouldn't be true, otherwise we are missing some logic in getMinTrailingZeros? Added an assert that the check isn't true.

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@preames preames Sep 26, 2024

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With the reframing of urem (B, 1 << Mult2) == 0, I agree with your comment, but I think we could reasonable see divergence with the original urem(B,A) check. Those are just different enough.

My suggestion is basically, can we prove the original fact without using the trailing bits proof strategy? Said differently. what if D = gcd(A, N) is something like 3^M?

Hm, though now I see that the multiplicative inverse code below would need updated too. I'd missed that originally.

(Totally fine to move forward here, this is purely a possible followup.)

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@fhahn fhahn Sep 27, 2024

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I stand corrected, the assertion actually uncovered a case where getMinTrailingZeros returns a worse result and I think catching this in getMinTrailingZeros would require matching a specific pattern (https://alive2.llvm.org/ce/z/t3A5X2)

I updated the code to check if the URem is zero if the trailing bits check failed, as we need to build the expression there already. Test is in llvm/test/Analysis/ScalarEvolution/trip-count-urem.ll

if (!Predicates)
return SE.getCouldNotCompute();
// Try to add a predicate ensuring B is a multiple of 1 << Mult2.
const SCEV *URem =
SE.getURemExpr(B, SE.getConstant(APInt::getOneBitSet(BW, Mult2)));
const SCEV *Zero = SE.getZero(B->getType());
assert(!SE.isKnownPredicate(CmpInst::ICMP_EQ, URem, Zero) &&
"No remainder for 1 << Mult2 but missed by getTrailingBits?");
// Avoid adding a predicate that is known to be false.
if (SE.isKnownPredicate(CmpInst::ICMP_NE, URem, Zero))
return SE.getCouldNotCompute();
Predicates->insert(SE.getEqualPredicate(URem, Zero));
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@david-arm david-arm Sep 16, 2024

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Just thinking in terms of compile-time here - can you get the equivalent result if you first compute SE.getEqualPredicate(URem, Zero) and then test if the answer is constant-false? I don't know if isKnownPredicate is expensive or not and whether or not we care.

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@fhahn fhahn Sep 26, 2024

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I think the terminology is a bit confusing, the predicate in isKnownPredicate refers to condition to check for the arguments, while predicate in getEqualPredicate refers to a SCEVPredicate (used by PredicateScalarEvolution) and those cannot be used by the isKnownPredicate helpers AFAIK

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@david-arm david-arm Sep 27, 2024

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OK that's fair enough! Thanks for the explanation

}

// 3. Compute I: the multiplicative inverse of (A / D) in arithmetic
// modulo (N / D).
Expand Down Expand Up @@ -10577,8 +10592,9 @@ ScalarEvolution::ExitLimit ScalarEvolution::howFarToZero(const SCEV *V,
// Solve the general equation.
if (!StepC || StepC->getValue()->isZero())
return getCouldNotCompute();
const SCEV *E = SolveLinEquationWithOverflow(StepC->getAPInt(),
getNegativeSCEV(Start), *this);
const SCEV *E = SolveLinEquationWithOverflow(
StepC->getAPInt(), getNegativeSCEV(Start),
AllowPredicates ? &Predicates : nullptr, *this);

const SCEV *M = E;
if (E != getCouldNotCompute()) {
Expand Down
39 changes: 35 additions & 4 deletions llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -1580,6 +1580,15 @@ define i32 @ptr_induction_ult_2(ptr %a, ptr %b) {
; CHECK-NEXT: Loop %loop: Unpredictable backedge-taken count.
; CHECK-NEXT: Loop %loop: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %loop: Unpredictable symbolic max backedge-taken count.
; CHECK-NEXT: Loop %loop: Predicated backedge-taken count is (((-1 * (ptrtoint ptr %a to i64)) + (ptrtoint ptr %b to i64)) /u 4)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i2 ((trunc i64 (ptrtoint ptr %b to i64) to i2) + (-1 * (trunc i64 (ptrtoint ptr %a to i64) to i2))) to i64) == 0
; CHECK-NEXT: Loop %loop: Predicated constant max backedge-taken count is i64 4611686018427387903
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i2 ((trunc i64 (ptrtoint ptr %b to i64) to i2) + (-1 * (trunc i64 (ptrtoint ptr %a to i64) to i2))) to i64) == 0
; CHECK-NEXT: Loop %loop: Predicated symbolic max backedge-taken count is (((-1 * (ptrtoint ptr %a to i64)) + (ptrtoint ptr %b to i64)) /u 4)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i2 ((trunc i64 (ptrtoint ptr %b to i64) to i2) + (-1 * (trunc i64 (ptrtoint ptr %a to i64) to i2))) to i64) == 0
;
entry:
%cmp.6 = icmp ult ptr %a, %b
Expand All @@ -1606,6 +1615,15 @@ define i32 @ptr_induction_ult_3_step_6(ptr %a, ptr %b) {
; CHECK-NEXT: Loop %loop: Unpredictable backedge-taken count.
; CHECK-NEXT: Loop %loop: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %loop: Unpredictable symbolic max backedge-taken count.
; CHECK-NEXT: Loop %loop: Predicated backedge-taken count is (((3074457345618258603 * (ptrtoint ptr %b to i64)) + (-3074457345618258603 * (ptrtoint ptr %a to i64))) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i64 ((-1 * (ptrtoint ptr %a to i64)) + (ptrtoint ptr %b to i64)) to i1) to i64) == 0
; CHECK-NEXT: Loop %loop: Predicated constant max backedge-taken count is i64 9223372036854775807
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i64 ((-1 * (ptrtoint ptr %a to i64)) + (ptrtoint ptr %b to i64)) to i1) to i64) == 0
; CHECK-NEXT: Loop %loop: Predicated symbolic max backedge-taken count is (((3074457345618258603 * (ptrtoint ptr %b to i64)) + (-3074457345618258603 * (ptrtoint ptr %a to i64))) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i64 ((-1 * (ptrtoint ptr %a to i64)) + (ptrtoint ptr %b to i64)) to i1) to i64) == 0
;
entry:
%cmp.6 = icmp ult ptr %a, %b
Expand Down Expand Up @@ -1705,10 +1723,9 @@ exit:
ret void
}

; TODO: It feels like we should be able to calculate the symbolic max
; exit count for the loop.inc block here, in the same way as
; ptr_induction_eq_1. The problem seems to be in howFarToZero when the
; ControlsOnlyExit is set to false.
; %a and %b may not have the same alignment, so the loop may only via the early
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@david-arm david-arm Sep 16, 2024

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nit: s/so the loop may only via/so the loop may only exit via/

; exit when %ptr.iv > %b. The predicated exit count for the latch can be
; computed by adding a predicate.
define void @ptr_induction_early_exit_eq_1(ptr %a, ptr %b, ptr %c) {
; CHECK-LABEL: 'ptr_induction_early_exit_eq_1'
; CHECK-NEXT: Classifying expressions for: @ptr_induction_early_exit_eq_1
Expand All @@ -1722,10 +1739,24 @@ define void @ptr_induction_early_exit_eq_1(ptr %a, ptr %b, ptr %c) {
; CHECK-NEXT: Loop %loop: <multiple exits> Unpredictable backedge-taken count.
; CHECK-NEXT: exit count for loop: ***COULDNOTCOMPUTE***
; CHECK-NEXT: exit count for loop.inc: ***COULDNOTCOMPUTE***
; CHECK-NEXT: predicated exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a to i64)) + (ptrtoint ptr %b to i64)) /u 8)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i3 ((trunc i64 (ptrtoint ptr %b to i64) to i3) + (-1 * (trunc i64 (ptrtoint ptr %a to i64) to i3))) to i64) == 0
; CHECK-EMPTY:
; CHECK-NEXT: Loop %loop: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %loop: Unpredictable symbolic max backedge-taken count.
; CHECK-NEXT: symbolic max exit count for loop: ***COULDNOTCOMPUTE***
; CHECK-NEXT: symbolic max exit count for loop.inc: ***COULDNOTCOMPUTE***
; CHECK-NEXT: predicated symbolic max exit count for loop.inc: ((-8 + (-1 * (ptrtoint ptr %a to i64)) + (ptrtoint ptr %b to i64)) /u 8)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i3 ((trunc i64 (ptrtoint ptr %b to i64) to i3) + (-1 * (trunc i64 (ptrtoint ptr %a to i64) to i3))) to i64) == 0
; CHECK-EMPTY:
; CHECK-NEXT: Loop %loop: Predicated constant max backedge-taken count is i64 2305843009213693951
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i3 ((trunc i64 (ptrtoint ptr %b to i64) to i3) + (-1 * (trunc i64 (ptrtoint ptr %a to i64) to i3))) to i64) == 0
; CHECK-NEXT: Loop %loop: Predicated symbolic max backedge-taken count is ((-8 + (-1 * (ptrtoint ptr %a to i64)) + (ptrtoint ptr %b to i64)) /u 8)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i3 ((trunc i64 (ptrtoint ptr %b to i64) to i3) + (-1 * (trunc i64 (ptrtoint ptr %a to i64) to i3))) to i64) == 0
;
entry:
%cmp = icmp eq ptr %a, %b
Expand Down
101 changes: 101 additions & 0 deletions llvm/test/Analysis/ScalarEvolution/ne-overflow.ll
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Expand Up @@ -58,6 +58,15 @@ define void @test_well_defined_infinite_st(i32 %N) mustprogress {
; CHECK-NEXT: Loop %for.body: Unpredictable backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable symbolic max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is ((-2 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
; CHECK-NEXT: Loop %for.body: Predicated constant max backedge-taken count is i32 2147483647
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
; CHECK-NEXT: Loop %for.body: Predicated symbolic max backedge-taken count is ((-2 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
;
entry:
br label %for.body
Expand All @@ -79,6 +88,15 @@ define void @test_well_defined_infinite_ld(i32 %N) mustprogress {
; CHECK-NEXT: Loop %for.body: Unpredictable backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable symbolic max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is ((-2 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
; CHECK-NEXT: Loop %for.body: Predicated constant max backedge-taken count is i32 2147483647
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
; CHECK-NEXT: Loop %for.body: Predicated symbolic max backedge-taken count is ((-2 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
;
entry:
br label %for.body
Expand All @@ -100,6 +118,15 @@ define void @test_no_mustprogress(i32 %N) {
; CHECK-NEXT: Loop %for.body: Unpredictable backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable symbolic max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is ((-2 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
; CHECK-NEXT: Loop %for.body: Predicated constant max backedge-taken count is i32 2147483647
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
; CHECK-NEXT: Loop %for.body: Predicated symbolic max backedge-taken count is ((-2 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
;
entry:
br label %for.body
Expand Down Expand Up @@ -187,6 +214,15 @@ define void @test_abnormal_exit(i32 %N) mustprogress {
; CHECK-NEXT: Loop %for.body: Unpredictable backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable symbolic max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is ((-2 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
; CHECK-NEXT: Loop %for.body: Predicated constant max backedge-taken count is i32 2147483647
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
; CHECK-NEXT: Loop %for.body: Predicated symbolic max backedge-taken count is ((-2 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
;
entry:
br label %for.body
Expand All @@ -209,10 +245,24 @@ define void @test_other_exit(i32 %N) mustprogress {
; CHECK-NEXT: Loop %for.body: <multiple exits> Unpredictable backedge-taken count.
; CHECK-NEXT: exit count for for.body: i32 9
; CHECK-NEXT: exit count for for.latch: ***COULDNOTCOMPUTE***
; CHECK-NEXT: predicated exit count for for.latch: ((-2 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
; CHECK-EMPTY:
; CHECK-NEXT: Loop %for.body: constant max backedge-taken count is i32 9
; CHECK-NEXT: Loop %for.body: symbolic max backedge-taken count is i32 9
; CHECK-NEXT: symbolic max exit count for for.body: i32 9
; CHECK-NEXT: symbolic max exit count for for.latch: ***COULDNOTCOMPUTE***
; CHECK-NEXT: predicated symbolic max exit count for for.latch: ((-2 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
; CHECK-EMPTY:
; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is (9 umin ((-2 + %N) /u 2))
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
; CHECK-NEXT: Loop %for.body: Predicated symbolic max backedge-taken count is (9 umin ((-2 + %N) /u 2))
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i32 %N to i1) to i32) == 0
;
entry:
br label %for.body
Expand Down Expand Up @@ -267,6 +317,18 @@ define void @test_sext(i64 %N) mustprogress {
; CHECK-NEXT: Loop %for.body: Unpredictable backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable symbolic max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is (%N /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nssw>
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i64 %N to i1) to i64) == 0
; CHECK-NEXT: Loop %for.body: Predicated constant max backedge-taken count is i64 9223372036854775807
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nssw>
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i64 %N to i1) to i64) == 0
; CHECK-NEXT: Loop %for.body: Predicated symbolic max backedge-taken count is (%N /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nssw>
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i64 %N to i1) to i64) == 0
;
entry:
br label %for.body
Expand All @@ -288,6 +350,21 @@ define void @test_zext_of_sext(i64 %N) mustprogress {
; CHECK-NEXT: Loop %for.body: Unpredictable backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable symbolic max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is (%N /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nssw>
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nusw>
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i64 %N to i1) to i64) == 0
; CHECK-NEXT: Loop %for.body: Predicated constant max backedge-taken count is i64 9223372036854775807
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nssw>
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nusw>
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i64 %N to i1) to i64) == 0
; CHECK-NEXT: Loop %for.body: Predicated symbolic max backedge-taken count is (%N /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nssw>
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nusw>
; CHECK-NEXT: Equal predicate: (zext i1 (trunc i64 %N to i1) to i64) == 0
;
entry:
br label %for.body
Expand All @@ -310,6 +387,18 @@ define void @test_zext_offset(i64 %N) mustprogress {
; CHECK-NEXT: Loop %for.body: Unpredictable backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable symbolic max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is ((-21 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nusw>
; CHECK-NEXT: Equal predicate: (zext i1 (true + (trunc i64 %N to i1)) to i64) == 0
; CHECK-NEXT: Loop %for.body: Predicated constant max backedge-taken count is i64 9223372036854775807
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nusw>
; CHECK-NEXT: Equal predicate: (zext i1 (true + (trunc i64 %N to i1)) to i64) == 0
; CHECK-NEXT: Loop %for.body: Predicated symbolic max backedge-taken count is ((-21 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nusw>
; CHECK-NEXT: Equal predicate: (zext i1 (true + (trunc i64 %N to i1)) to i64) == 0
;
entry:
br label %for.body
Expand All @@ -332,6 +421,18 @@ define void @test_sext_offset(i64 %N) mustprogress {
; CHECK-NEXT: Loop %for.body: Unpredictable backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable symbolic max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is ((-21 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nssw>
; CHECK-NEXT: Equal predicate: (zext i1 (true + (trunc i64 %N to i1)) to i64) == 0
; CHECK-NEXT: Loop %for.body: Predicated constant max backedge-taken count is i64 9223372036854775807
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nssw>
; CHECK-NEXT: Equal predicate: (zext i1 (true + (trunc i64 %N to i1)) to i64) == 0
; CHECK-NEXT: Loop %for.body: Predicated symbolic max backedge-taken count is ((-21 + %N) /u 2)
; CHECK-NEXT: Predicates:
; CHECK-NEXT: {0,+,2}<%for.body> Added Flags: <nssw>
; CHECK-NEXT: Equal predicate: (zext i1 (true + (trunc i64 %N to i1)) to i64) == 0
;
entry:
br label %for.body
Expand Down
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