[llvm] a10a64e - [SCEV] Recommit "Use nw flag and symbolic iteration count to sharpen ranges of AddRecs", attempt 2
Max Kazantsev via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 19 21:33:03 PDT 2020
Author: Max Kazantsev
Date: 2020-10-20T11:32:36+07:00
New Revision: a10a64e7e334dc878d281aba9a46f751fe606567
URL: https://github.com/llvm/llvm-project/commit/a10a64e7e334dc878d281aba9a46f751fe606567
DIFF: https://github.com/llvm/llvm-project/commit/a10a64e7e334dc878d281aba9a46f751fe606567.diff
LOG: [SCEV] Recommit "Use nw flag and symbolic iteration count to sharpen ranges of AddRecs", attempt 2
Fixed wrapping range case & proof methods reduced to constant range
checks to save compile time.
Differential Revision: https://reviews.llvm.org/D89381
Added:
Modified:
llvm/include/llvm/Analysis/ScalarEvolution.h
llvm/lib/Analysis/ScalarEvolution.cpp
llvm/test/Analysis/ScalarEvolution/no-wrap-symbolic-becount.ll
llvm/test/Transforms/IndVarSimplify/X86/eliminate-trunc.ll
llvm/test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll
Removed:
################################################################################
diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index 85c04a79ba45..691c424a280c 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -1497,6 +1497,13 @@ class ScalarEvolution {
ConstantRange getRangeForAffineAR(const SCEV *Start, const SCEV *Stop,
const SCEV *MaxBECount, unsigned BitWidth);
+ /// Determines the range for the affine non-self-wrapping SCEVAddRecExpr {\p
+ /// Start,+,\p Stop}<nw>.
+ ConstantRange getRangeForAffineNoSelfWrappingAR(const SCEVAddRecExpr *AddRec,
+ const SCEV *MaxBECount,
+ unsigned BitWidth,
+ RangeSignHint SignHint);
+
/// Try to compute a range for the affine SCEVAddRecExpr {\p Start,+,\p
/// Stop} by "factoring out" a ternary expression from the add recurrence.
/// Helper called by \c getRange.
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index efc4600e248f..b9c6cf8f1338 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -5527,6 +5527,17 @@ ScalarEvolution::getRangeRef(const SCEV *S,
ConservativeResult =
ConservativeResult.intersectWith(RangeFromFactoring, RangeType);
}
+
+ // Now try symbolic BE count and more powerful methods.
+ MaxBECount = computeMaxBackedgeTakenCount(AddRec->getLoop());
+ if (!isa<SCEVCouldNotCompute>(MaxBECount) &&
+ getTypeSizeInBits(MaxBECount->getType()) <= BitWidth &&
+ AddRec->hasNoSelfWrap()) {
+ auto RangeFromAffineNew = getRangeForAffineNoSelfWrappingAR(
+ AddRec, MaxBECount, BitWidth, SignHint);
+ ConservativeResult =
+ ConservativeResult.intersectWith(RangeFromAffineNew, RangeType);
+ }
}
return setRange(AddRec, SignHint, std::move(ConservativeResult));
@@ -5696,6 +5707,70 @@ ConstantRange ScalarEvolution::getRangeForAffineAR(const SCEV *Start,
return SR.intersectWith(UR, ConstantRange::Smallest);
}
+ConstantRange ScalarEvolution::getRangeForAffineNoSelfWrappingAR(
+ const SCEVAddRecExpr *AddRec, const SCEV *MaxBECount, unsigned BitWidth,
+ ScalarEvolution::RangeSignHint SignHint) {
+ assert(AddRec->isAffine() && "Non-affine AddRecs are not suppored!\n");
+ assert(AddRec->hasNoSelfWrap() &&
+ "This only works for non-self-wrapping AddRecs!");
+ const bool IsSigned = SignHint == HINT_RANGE_SIGNED;
+ const SCEV *Step = AddRec->getStepRecurrence(*this);
+ // Let's make sure that we can prove that we do not self-wrap during
+ // MaxBECount iterations. We need this because MaxBECount is a maximum
+ // iteration count estimate, and we might infer nw from some exit for which we
+ // do not know max exit count (or any other side reasoning).
+ // TODO: Turn into assert at some point.
+ MaxBECount = getNoopOrZeroExtend(MaxBECount, AddRec->getType());
+ const SCEV *RangeWidth = getNegativeSCEV(getOne(AddRec->getType()));
+ const SCEV *StepAbs = getUMinExpr(Step, getNegativeSCEV(Step));
+ const SCEV *MaxItersWithoutWrap = getUDivExpr(RangeWidth, StepAbs);
+ if (!isKnownPredicate(ICmpInst::ICMP_ULE, MaxBECount, MaxItersWithoutWrap))
+ return ConstantRange::getFull(BitWidth);
+
+ ICmpInst::Predicate LEPred =
+ IsSigned ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE;
+ ICmpInst::Predicate GEPred =
+ IsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE;
+ const SCEV *Start = AddRec->getStart();
+ const SCEV *End = AddRec->evaluateAtIteration(MaxBECount, *this);
+
+ // We know that there is no self-wrap. Let's take Start and End values and
+ // look at all intermediate values V1, V2, ..., Vn that IndVar takes during
+ // the iteration. They either lie inside the range [Min(Start, End),
+ // Max(Start, End)] or outside it:
+ //
+ // Case 1: RangeMin ... Start V1 ... VN End ... RangeMax;
+ // Case 2: RangeMin Vk ... V1 Start ... End Vn ... Vk + 1 RangeMax;
+ //
+ // No self wrap flag guarantees that the intermediate values cannot be BOTH
+ // outside and inside the range [Min(Start, End), Max(Start, End)]. Using that
+ // knowledge, let's try to prove that we are dealing with Case 1. It is so if
+ // Start <= End and step is positive, or Start >= End and step is negative.
+ ConstantRange StartRange =
+ IsSigned ? getSignedRange(Start) : getUnsignedRange(Start);
+ ConstantRange EndRange =
+ IsSigned ? getSignedRange(End) : getUnsignedRange(End);
+ ConstantRange RangeBetween = StartRange.unionWith(EndRange);
+ // If they already cover full iteration space, we will know nothing useful
+ // even if we prove what we want to prove.
+ if (RangeBetween.isFullSet())
+ return RangeBetween;
+ // Only deal with ranges that do not wrap (i.e. RangeMin < RangeMax).
+ bool IsWrappingRange =
+ IsSigned ? RangeBetween.getLower().sge(RangeBetween.getUpper())
+ : RangeBetween.getLower().uge(RangeBetween.getUpper());
+ if (IsWrappingRange)
+ return ConstantRange::getFull(BitWidth);
+
+ if (isKnownPositive(Step) &&
+ isKnownPredicateViaConstantRanges(LEPred, Start, End))
+ return RangeBetween;
+ else if (isKnownNegative(Step) &&
+ isKnownPredicateViaConstantRanges(GEPred, Start, End))
+ return RangeBetween;
+ return ConstantRange::getFull(BitWidth);
+}
+
ConstantRange ScalarEvolution::getRangeViaFactoring(const SCEV *Start,
const SCEV *Step,
const SCEV *MaxBECount,
diff --git a/llvm/test/Analysis/ScalarEvolution/no-wrap-symbolic-becount.ll b/llvm/test/Analysis/ScalarEvolution/no-wrap-symbolic-becount.ll
index 77c1017edb1a..b49ec80c6d28 100644
--- a/llvm/test/Analysis/ScalarEvolution/no-wrap-symbolic-becount.ll
+++ b/llvm/test/Analysis/ScalarEvolution/no-wrap-symbolic-becount.ll
@@ -7,7 +7,7 @@ define i32 @test_01(i32 %start, i32* %p, i32* %q) {
; CHECK-NEXT: %0 = zext i32 %start to i64
; CHECK-NEXT: --> (zext i32 %start to i64) U: [0,4294967296) S: [0,4294967296)
; CHECK-NEXT: %indvars.iv = phi i64 [ %indvars.iv.next, %backedge ], [ %0, %entry ]
-; CHECK-NEXT: --> {(zext i32 %start to i64),+,-1}<nsw><%loop> U: [-4294967295,4294967296) S: [-4294967295,4294967296) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT: --> {(zext i32 %start to i64),+,-1}<nsw><%loop> U: [0,4294967296) S: [0,4294967296) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv = phi i32 [ %start, %entry ], [ %iv.next, %backedge ]
; CHECK-NEXT: --> {%start,+,-1}<%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.next = add i32 %iv, -1
@@ -21,7 +21,7 @@ define i32 @test_01(i32 %start, i32* %p, i32* %q) {
; CHECK-NEXT: %stop = load i32, i32* %load.addr, align 4
; CHECK-NEXT: --> %stop U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
; CHECK-NEXT: %indvars.iv.next = add nsw i64 %indvars.iv, -1
-; CHECK-NEXT: --> {(-1 + (zext i32 %start to i64))<nsw>,+,-1}<nsw><%loop> U: [-4294967296,4294967295) S: [-4294967296,4294967295) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT: --> {(-1 + (zext i32 %start to i64))<nsw>,+,-1}<nsw><%loop> U: [-4294967296,4294967295) S: [-1,4294967295) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
; CHECK-NEXT: Determining loop execution counts for: @test_01
; CHECK-NEXT: Loop %loop: <multiple exits> Unpredictable backedge-taken count.
; CHECK-NEXT: exit count for loop: (zext i32 %start to i64)
diff --git a/llvm/test/Transforms/IndVarSimplify/X86/eliminate-trunc.ll b/llvm/test/Transforms/IndVarSimplify/X86/eliminate-trunc.ll
index 9fb7977c207f..4738369c0aca 100644
--- a/llvm/test/Transforms/IndVarSimplify/X86/eliminate-trunc.ll
+++ b/llvm/test/Transforms/IndVarSimplify/X86/eliminate-trunc.ll
@@ -474,7 +474,7 @@ define void @test_10(i32 %n) {
; CHECK-NEXT: [[TMP1:%.*]] = zext i32 [[TMP0]] to i64
; CHECK-NEXT: [[TMP2:%.*]] = icmp ult i64 [[TMP1]], 90
; CHECK-NEXT: [[UMIN:%.*]] = select i1 [[TMP2]], i64 [[TMP1]], i64 90
-; CHECK-NEXT: [[TMP3:%.*]] = add i64 [[UMIN]], -99
+; CHECK-NEXT: [[TMP3:%.*]] = add nuw nsw i64 [[UMIN]], -99
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i64 [ -100, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
diff --git a/llvm/test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll b/llvm/test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll
index 5cc288c58e68..090efa44d9c0 100644
--- a/llvm/test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll
+++ b/llvm/test/Transforms/IndVarSimplify/promote-iv-to-eliminate-casts.ll
@@ -196,7 +196,7 @@ define void @promote_latch_condition_decrementing_loop_01(i32* %p, i32* %a) {
; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], [[LOOP]] ], [ [[TMP0]], [[PREHEADER]] ]
; CHECK-NEXT: [[EL:%.*]] = getelementptr inbounds i32, i32* [[A:%.*]], i64 [[INDVARS_IV]]
; CHECK-NEXT: store atomic i32 0, i32* [[EL]] unordered, align 4
-; CHECK-NEXT: [[LOOPCOND:%.*]] = icmp slt i64 [[INDVARS_IV]], 1
+; CHECK-NEXT: [[LOOPCOND:%.*]] = icmp ult i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nsw i64 [[INDVARS_IV]], -1
; CHECK-NEXT: br i1 [[LOOPCOND]], label [[LOOPEXIT_LOOPEXIT:%.*]], label [[LOOP]]
;
@@ -241,7 +241,7 @@ define void @promote_latch_condition_decrementing_loop_02(i32* %p, i32* %a) {
; CHECK-NEXT: [[EL:%.*]] = getelementptr inbounds i32, i32* [[A:%.*]], i64 [[INDVARS_IV]]
; CHECK-NEXT: store atomic i32 0, i32* [[EL]] unordered, align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nsw i64 [[INDVARS_IV]], -1
-; CHECK-NEXT: [[LOOPCOND:%.*]] = icmp slt i64 [[INDVARS_IV]], 1
+; CHECK-NEXT: [[LOOPCOND:%.*]] = icmp ult i64 [[INDVARS_IV]], 1
; CHECK-NEXT: br i1 [[LOOPCOND]], label [[LOOPEXIT_LOOPEXIT:%.*]], label [[LOOP]]
;
@@ -285,7 +285,7 @@ define void @promote_latch_condition_decrementing_loop_03(i32* %p, i32* %a) {
; CHECK-NEXT: [[EL:%.*]] = getelementptr inbounds i32, i32* [[A:%.*]], i64 [[INDVARS_IV]]
; CHECK-NEXT: store atomic i32 0, i32* [[EL]] unordered, align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nsw i64 [[INDVARS_IV]], -1
-; CHECK-NEXT: [[LOOPCOND:%.*]] = icmp slt i64 [[INDVARS_IV]], 1
+; CHECK-NEXT: [[LOOPCOND:%.*]] = icmp ult i64 [[INDVARS_IV]], 1
; CHECK-NEXT: br i1 [[LOOPCOND]], label [[LOOPEXIT_LOOPEXIT:%.*]], label [[LOOP]]
;
@@ -336,7 +336,7 @@ define void @promote_latch_condition_decrementing_loop_04(i32* %p, i32* %a, i1 %
; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], [[LOOP]] ], [ [[TMP0]], [[PREHEADER]] ]
; CHECK-NEXT: [[EL:%.*]] = getelementptr inbounds i32, i32* [[A:%.*]], i64 [[INDVARS_IV]]
; CHECK-NEXT: store atomic i32 0, i32* [[EL]] unordered, align 4
-; CHECK-NEXT: [[LOOPCOND:%.*]] = icmp slt i64 [[INDVARS_IV]], 1
+; CHECK-NEXT: [[LOOPCOND:%.*]] = icmp ult i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nsw i64 [[INDVARS_IV]], -1
; CHECK-NEXT: br i1 [[LOOPCOND]], label [[LOOPEXIT_LOOPEXIT:%.*]], label [[LOOP]]
;
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