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[SCEV] Compute ranges for lshr recurrences

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Straight forward extension to the recently added infrastructure which was pioneered with shl.

Differential Revision: https://reviews.llvm.org/D99687
This commit is contained in:
Philip Reames 2021-04-22 11:05:19 -07:00
parent 8361e53fbe
commit 555456c598
2 changed files with 26 additions and 12 deletions
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14
lib/Analysis/ScalarEvolution.cpp
View File

@ -5696,6 +5696,7 @@ getRangeForUnknownRecurrence(const SCEVUnknown *U) {
switch (BO->getOpcode()) {
default:
return CR;
case Instruction::LShr:
case Instruction::Shl:
break;
};
@ -5724,6 +5725,19 @@ getRangeForUnknownRecurrence(const SCEVUnknown *U) {
switch (BO->getOpcode()) {
default:
llvm_unreachable("filtered out above");
case Instruction::LShr: {
// For each lshr, three cases:
// shift = 0 => unchanged value
// saturation => 0
// other => a smaller positive number
// Thus, the low end of the unsigned range is the last value produced.
auto KnownEnd = KnownBits::lshr(KnownStart,
KnownBits::makeConstant(TotalShift));
auto R = ConstantRange::getNonEmpty(KnownEnd.getMinValue(),
KnownStart.getMaxValue() + 1);
CR = CR.intersectWith(R);
break;
}
case Instruction::Shl: {
// Iff no bits are shifted out, value increases on every shift.
auto KnownEnd = KnownBits::shl(KnownStart,

24
test/Analysis/ScalarEvolution/shift-recurrences.ll
View File

@ -630,11 +630,11 @@ define void @test_lshr_tc_positive() {
; CHECK-NEXT: %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
; CHECK-NEXT: --> {0,+,1}<%loop> U: [0,5) S: [0,5) Exits: 4 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr = phi i64 [ 1023, %entry ], [ %iv.lshr.next, %loop ]
; CHECK-NEXT: --> %iv.lshr U: [0,1024) S: [0,1024) Exits: 63 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> %iv.lshr U: [63,1024) S: [63,1024) Exits: 63 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: %iv.next = add i64 %iv, 1
; CHECK-NEXT: --> {1,+,1}<%loop> U: [1,6) S: [1,6) Exits: 5 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr.next = lshr i64 %iv.lshr, 1
; CHECK-NEXT: --> (%iv.lshr /u 2) U: [0,512) S: [0,512) Exits: 31 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> (%iv.lshr /u 2) U: [31,512) S: [31,512) Exits: 31 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: Determining loop execution counts for: @test_lshr_tc_positive
; CHECK-NEXT: Loop %loop: backedge-taken count is 4
; CHECK-NEXT: Loop %loop: max backedge-taken count is 4
@ -661,11 +661,11 @@ define void @test_lshr_tc_negative() {
; CHECK-NEXT: %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
; CHECK-NEXT: --> {0,+,1}<%loop> U: [0,5) S: [0,5) Exits: 4 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr = phi i8 [ -1, %entry ], [ %iv.lshr.next, %loop ]
; CHECK-NEXT: --> %iv.lshr U: [-1,-128) S: [-1,-128) Exits: 15 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> %iv.lshr U: [15,0) S: [-1,-128) Exits: 15 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: %iv.next = add i64 %iv, 1
; CHECK-NEXT: --> {1,+,1}<%loop> U: [1,6) S: [1,6) Exits: 5 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr.next = lshr i8 %iv.lshr, 1
; CHECK-NEXT: --> (%iv.lshr /u 2) U: [0,-128) S: [0,-128) Exits: 7 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> (%iv.lshr /u 2) U: [7,-128) S: [7,-128) Exits: 7 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: Determining loop execution counts for: @test_lshr_tc_negative
; CHECK-NEXT: Loop %loop: backedge-taken count is 4
; CHECK-NEXT: Loop %loop: max backedge-taken count is 4
@ -726,11 +726,11 @@ define void @test_lshr_zero_shift() {
; CHECK-NEXT: %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
; CHECK-NEXT: --> {0,+,1}<%loop> U: [0,5) S: [0,5) Exits: 4 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr = phi i64 [ 1023, %entry ], [ %iv.lshr.next, %loop ]
; CHECK-NEXT: --> %iv.lshr U: [0,1024) S: [0,1024) Exits: 1023 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> %iv.lshr U: [1023,1024) S: [1023,1024) Exits: 1023 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: %iv.next = add i64 %iv, 1
; CHECK-NEXT: --> {1,+,1}<%loop> U: [1,6) S: [1,6) Exits: 5 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr.next = lshr i64 %iv.lshr, 0
; CHECK-NEXT: --> %iv.lshr U: [0,1024) S: [0,1024) Exits: 1023 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> %iv.lshr U: [1023,1024) S: [1023,1024) Exits: 1023 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: Determining loop execution counts for: @test_lshr_zero_shift
; CHECK-NEXT: Loop %loop: backedge-taken count is 4
; CHECK-NEXT: Loop %loop: max backedge-taken count is 4
@ -758,11 +758,11 @@ define void @test_lshr_power_of_2_start() {
; CHECK-NEXT: %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
; CHECK-NEXT: --> {0,+,1}<%loop> U: [0,5) S: [0,5) Exits: 4 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr = phi i64 [ 1024, %entry ], [ %iv.lshr.next, %loop ]
; CHECK-NEXT: --> %iv.lshr U: [0,1025) S: [0,1025) Exits: 4 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> %iv.lshr U: [4,1025) S: [4,1025) Exits: 4 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: %iv.next = add i64 %iv, 1
; CHECK-NEXT: --> {1,+,1}<%loop> U: [1,6) S: [1,6) Exits: 5 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr.next = lshr i64 %iv.lshr, 2
; CHECK-NEXT: --> (%iv.lshr /u 4) U: [0,512) S: [0,512) Exits: 1 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> (%iv.lshr /u 4) U: [1,257) S: [1,257) Exits: 1 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: Determining loop execution counts for: @test_lshr_power_of_2_start
; CHECK-NEXT: Loop %loop: backedge-taken count is 4
; CHECK-NEXT: Loop %loop: max backedge-taken count is 4
@ -790,11 +790,11 @@ define void @test_lshr_arbitrary_start() {
; CHECK-NEXT: %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
; CHECK-NEXT: --> {0,+,1}<%loop> U: [0,5) S: [0,5) Exits: 4 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr = phi i64 [ 957, %entry ], [ %iv.lshr.next, %loop ]
; CHECK-NEXT: --> %iv.lshr U: [0,958) S: [0,958) Exits: 3 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> %iv.lshr U: [3,958) S: [3,958) Exits: 3 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: %iv.next = add i64 %iv, 1
; CHECK-NEXT: --> {1,+,1}<%loop> U: [1,6) S: [1,6) Exits: 5 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr.next = lshr i64 %iv.lshr, 2
; CHECK-NEXT: --> (%iv.lshr /u 4) U: [0,256) S: [0,256) Exits: 0 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> (%iv.lshr /u 4) U: [0,240) S: [0,240) Exits: 0 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: Determining loop execution counts for: @test_lshr_arbitrary_start
; CHECK-NEXT: Loop %loop: backedge-taken count is 4
; CHECK-NEXT: Loop %loop: max backedge-taken count is 4
@ -821,11 +821,11 @@ define void @test_lshr_start_power_of_2_plus_one() {
; CHECK-NEXT: %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
; CHECK-NEXT: --> {0,+,1}<%loop> U: [0,5) S: [0,5) Exits: 4 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr = phi i64 [ 1025, %entry ], [ %iv.lshr.next, %loop ]
; CHECK-NEXT: --> %iv.lshr U: [0,1026) S: [0,1026) Exits: 4 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> %iv.lshr U: [4,1026) S: [4,1026) Exits: 4 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: %iv.next = add i64 %iv, 1
; CHECK-NEXT: --> {1,+,1}<%loop> U: [1,6) S: [1,6) Exits: 5 LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.lshr.next = lshr i64 %iv.lshr, 2
; CHECK-NEXT: --> (%iv.lshr /u 4) U: [0,512) S: [0,512) Exits: 1 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: --> (%iv.lshr /u 4) U: [1,257) S: [1,257) Exits: 1 LoopDispositions: { %loop: Variant }
; CHECK-NEXT: Determining loop execution counts for: @test_lshr_start_power_of_2_plus_one
; CHECK-NEXT: Loop %loop: backedge-taken count is 4
; CHECK-NEXT: Loop %loop: max backedge-taken count is 4