[llvm] d480f96 - Revert "[SCEV] Model `ashr exact x, C` as `(abs(x) EXACT/u (1<<C)) * signum(x)`"
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Sun Apr 18 06:27:11 PDT 2021
Author: Roman Lebedev
Date: 2021-04-18T16:26:45+03:00
New Revision: d480f968ad8b56d3ee4a6b6df5532d485b0ad01e
URL: https://github.com/llvm/llvm-project/commit/d480f968ad8b56d3ee4a6b6df5532d485b0ad01e
DIFF: https://github.com/llvm/llvm-project/commit/d480f968ad8b56d3ee4a6b6df5532d485b0ad01e.diff
LOG: Revert "[SCEV] Model `ashr exact x, C` as `(abs(x) EXACT/u (1<<C)) * signum(x)`"
As being discussed in https://reviews.llvm.org/D100721,
this modelling is lossy, we can't reconstruct `ash`/`ashr exact`
from it, which means that whenever we actually expand the IR,
we've just pessimized the code..
It would be good to model this pattern, after all it comes up every time
you want to compute a distance between two pointers, but not at this cost.
This reverts commit ec54867df5e7f20e12146e628af34f0384308bcb.
Added:
Modified:
llvm/include/llvm/Analysis/ScalarEvolution.h
llvm/lib/Analysis/ScalarEvolution.cpp
llvm/test/Analysis/ScalarEvolution/ashr.ll
llvm/test/Analysis/ScalarEvolution/ptrtoint.ll
llvm/test/Transforms/IndVarSimplify/ashr-expansion.ll
Removed:
################################################################################
diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index 8407be99a82b1..ccdf29cf3a187 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -575,7 +575,6 @@ class ScalarEvolution {
const SCEV *getGEPExpr(GEPOperator *GEP,
const SmallVectorImpl<const SCEV *> &IndexExprs);
const SCEV *getAbsExpr(const SCEV *Op, bool IsNSW);
- const SCEV *getSignumExpr(const SCEV *Op);
const SCEV *getMinMaxExpr(SCEVTypes Kind,
SmallVectorImpl<const SCEV *> &Operands);
const SCEV *getSMaxExpr(const SCEV *LHS, const SCEV *RHS);
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 4630c5562623c..f92cccd448167 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3503,11 +3503,6 @@ const SCEV *ScalarEvolution::getAbsExpr(const SCEV *Op, bool IsNSW) {
return getSMaxExpr(Op, getNegativeSCEV(Op, Flags));
}
-const SCEV *ScalarEvolution::getSignumExpr(const SCEV *Op) {
- Type *Ty = Op->getType();
- return getSMinExpr(getSMaxExpr(Op, getMinusOne(Ty)), getOne(Ty));
-}
-
const SCEV *ScalarEvolution::getMinMaxExpr(SCEVTypes Kind,
SmallVectorImpl<const SCEV *> &Ops) {
assert(!Ops.empty() && "Cannot get empty (u|s)(min|max)!");
@@ -4559,7 +4554,6 @@ struct BinaryOp {
Value *RHS;
bool IsNSW = false;
bool IsNUW = false;
- bool IsExact = false;
/// Op is set if this BinaryOp corresponds to a concrete LLVM instruction or
/// constant expression.
@@ -4572,14 +4566,11 @@ struct BinaryOp {
IsNSW = OBO->hasNoSignedWrap();
IsNUW = OBO->hasNoUnsignedWrap();
}
- if (auto *PEO = dyn_cast<PossiblyExactOperator>(Op))
- IsExact = PEO->isExact();
}
explicit BinaryOp(unsigned Opcode, Value *LHS, Value *RHS, bool IsNSW = false,
- bool IsNUW = false, bool IsExact = false)
- : Opcode(Opcode), LHS(LHS), RHS(RHS), IsNSW(IsNSW), IsNUW(IsNUW),
- IsExact(IsExact) {}
+ bool IsNUW = false)
+ : Opcode(Opcode), LHS(LHS), RHS(RHS), IsNSW(IsNSW), IsNUW(IsNUW) {}
};
} // end anonymous namespace
@@ -6745,15 +6736,6 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
}
}
}
- if (BO->IsExact) {
- // Given exact arithmetic in-bounds right-shift by a constant,
- // we can lower it into: (abs(x) EXACT/u (1<<C)) * signum(x)
- const SCEV *X = getSCEV(BO->LHS);
- const SCEV *AbsX = getAbsExpr(X, /*IsNSW=*/false);
- APInt Mult = APInt::getOneBitSet(BitWidth, AShrAmt);
- const SCEV *Div = getUDivExactExpr(AbsX, getConstant(Mult));
- return getMulExpr(Div, getSignumExpr(X), SCEV::FlagNSW);
- }
break;
}
}
diff --git a/llvm/test/Analysis/ScalarEvolution/ashr.ll b/llvm/test/Analysis/ScalarEvolution/ashr.ll
index 0da69e5d082f6..b8bf8a42fbb64 100644
--- a/llvm/test/Analysis/ScalarEvolution/ashr.ll
+++ b/llvm/test/Analysis/ScalarEvolution/ashr.ll
@@ -42,7 +42,7 @@ define i32 @t3(i32 %x, i32 %y) {
; CHECK-LABEL: 't3'
; CHECK-NEXT: Classifying expressions for: @t3
; CHECK-NEXT: %i0 = ashr exact i32 %x, 4
-; CHECK-NEXT: --> ((((-1 * %x) smax %x) /u 16) * (1 smin (-1 smax %x)))<nsw> U: [-268435455,268435456) S: [-268435455,268435456)
+; CHECK-NEXT: --> %i0 U: [-134217728,134217728) S: [-134217728,134217728)
; CHECK-NEXT: Determining loop execution counts for: @t3
;
%i0 = ashr exact i32 %x, 4
@@ -65,7 +65,7 @@ define i32 @t5(i32 %x, i32 %y) {
; CHECK-LABEL: 't5'
; CHECK-NEXT: Classifying expressions for: @t5
; CHECK-NEXT: %i0 = ashr exact i32 %x, 5
-; CHECK-NEXT: --> ((((-1 * %x) smax %x) /u 32) * (1 smin (-1 smax %x)))<nsw> U: [-134217727,134217728) S: [-134217727,134217728)
+; CHECK-NEXT: --> %i0 U: [-67108864,67108864) S: [-67108864,67108864)
; CHECK-NEXT: Determining loop execution counts for: @t5
;
%i0 = ashr exact i32 %x, 5
diff --git a/llvm/test/Analysis/ScalarEvolution/ptrtoint.ll b/llvm/test/Analysis/ScalarEvolution/ptrtoint.ll
index 3c3da6c4daabe..6f5785f42b92a 100644
--- a/llvm/test/Analysis/ScalarEvolution/ptrtoint.ll
+++ b/llvm/test/Analysis/ScalarEvolution/ptrtoint.ll
@@ -473,9 +473,9 @@ define void @pr46786_c26_int(i32* %arg, i32* %arg1, i32* %arg2) {
; X64-NEXT: %i10 = sub i64 %i9, %i4
; X64-NEXT: --> {0,+,4}<nw><%bb6> U: [0,-3) S: [-9223372036854775808,9223372036854775805) Exits: (4 * ((-4 + (-1 * %arg) + %arg1) /u 4))<nuw> LoopDispositions: { %bb6: Computable }
; X64-NEXT: %i11 = ashr exact i64 %i10, 2
-; X64-NEXT: --> ((({0,+,4}<nw><%bb6> smax {0,+,-4}<nw><%bb6>) /u 4) * (1 smin (-1 smax {0,+,4}<nw><%bb6>)))<nsw> U: [-4611686018427387903,4611686018427387904) S: [-4611686018427387903,4611686018427387904) Exits: ((((4 * ((-4 + (-1 * %arg) + %arg1) /u 4))<nuw> smax (-4 * ((-4 + (-1 * %arg) + %arg1) /u 4))) /u 4) * (1 smin (-1 smax (4 * ((-4 + (-1 * %arg) + %arg1) /u 4))<nuw>)))<nsw> LoopDispositions: { %bb6: Computable }
+; X64-NEXT: --> %i11 U: [-2305843009213693952,2305843009213693952) S: [-2305843009213693952,2305843009213693952) Exits: <<Unknown>> LoopDispositions: { %bb6: Variant }
; X64-NEXT: %i12 = getelementptr inbounds i32, i32* %arg2, i64 %i11
-; X64-NEXT: --> ((4 * (({0,+,4}<nw><%bb6> smax {0,+,-4}<nw><%bb6>) /u 4) * (1 smin (-1 smax {0,+,4}<nw><%bb6>))) + %arg2) U: full-set S: full-set Exits: ((4 * (((4 * ((-4 + (-1 * %arg) + %arg1) /u 4))<nuw> smax (-4 * ((-4 + (-1 * %arg) + %arg1) /u 4))) /u 4) * (1 smin (-1 smax (4 * ((-4 + (-1 * %arg) + %arg1) /u 4))<nuw>))) + %arg2) LoopDispositions: { %bb6: Computable }
+; X64-NEXT: --> ((4 * %i11)<nsw> + %arg2) U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %bb6: Variant }
; X64-NEXT: %i13 = load i32, i32* %i12, align 4
; X64-NEXT: --> %i13 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %bb6: Variant }
; X64-NEXT: %i14 = add nsw i32 %i13, %i8
@@ -502,9 +502,9 @@ define void @pr46786_c26_int(i32* %arg, i32* %arg1, i32* %arg2) {
; X32-NEXT: %i10 = sub i64 %i9, %i4
; X32-NEXT: --> {0,+,4}<nw><%bb6> U: [0,4294967293) S: [0,4294967293) Exits: (4 * ((zext i32* (-4 + (-1 * %arg) + %arg1) to i64) /u 4))<nuw><nsw> LoopDispositions: { %bb6: Computable }
; X32-NEXT: %i11 = ashr exact i64 %i10, 2
-; X32-NEXT: --> ({0,+,1}<nw><%bb6> * (1 smin {0,+,4}<nuw><nsw><%bb6>))<nuw><nsw> U: [0,1073741824) S: [0,1073741824) Exits: (((zext i32* (-4 + (-1 * %arg) + %arg1) to i64) /u 4) * (1 smin (4 * ((zext i32* (-4 + (-1 * %arg) + %arg1) to i64) /u 4))<nuw><nsw>))<nuw><nsw> LoopDispositions: { %bb6: Computable }
+; X32-NEXT: --> %i11 U: [-2147483648,2147483648) S: [-2147483648,2147483648) Exits: <<Unknown>> LoopDispositions: { %bb6: Variant }
; X32-NEXT: %i12 = getelementptr inbounds i32, i32* %arg2, i64 %i11
-; X32-NEXT: --> (((trunc i64 (1 smin {0,+,4}<nuw><nsw><%bb6>) to i32) * {0,+,4}<%bb6>) + %arg2) U: full-set S: full-set Exits: ((4 * (trunc i64 (1 smin (4 * ((zext i32* (-4 + (-1 * %arg) + %arg1) to i64) /u 4))<nuw><nsw>) to i32) * ((-4 + (-1 * %arg) + %arg1) /u 4)) + %arg2) LoopDispositions: { %bb6: Computable }
+; X32-NEXT: --> ((4 * (trunc i64 %i11 to i32))<nsw> + %arg2) U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %bb6: Variant }
; X32-NEXT: %i13 = load i32, i32* %i12, align 4
; X32-NEXT: --> %i13 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %bb6: Variant }
; X32-NEXT: %i14 = add nsw i32 %i13, %i8
diff --git a/llvm/test/Transforms/IndVarSimplify/ashr-expansion.ll b/llvm/test/Transforms/IndVarSimplify/ashr-expansion.ll
index a4eb654d28fcf..23dbeffffd24e 100644
--- a/llvm/test/Transforms/IndVarSimplify/ashr-expansion.ll
+++ b/llvm/test/Transforms/IndVarSimplify/ashr-expansion.ll
@@ -6,13 +6,8 @@ target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
define float @ashr_expansion_valid(i64 %x, float* %ptr) {
; CHECK-LABEL: @ashr_expansion_valid(
; CHECK-NEXT: entry:
-; CHECK-NEXT: [[SMAX:%.*]] = call i64 @llvm.smax.i64(i64 [[X:%.*]], i64 -1)
-; CHECK-NEXT: [[SMIN:%.*]] = call i64 @llvm.smin.i64(i64 [[SMAX]], i64 1)
-; CHECK-NEXT: [[TMP0:%.*]] = sub i64 0, [[X]]
-; CHECK-NEXT: [[SMAX1:%.*]] = call i64 @llvm.smax.i64(i64 [[X]], i64 [[TMP0]])
-; CHECK-NEXT: [[TMP1:%.*]] = lshr i64 [[SMAX1]], 4
-; CHECK-NEXT: [[TMP2:%.*]] = mul nsw i64 [[SMIN]], [[TMP1]]
-; CHECK-NEXT: [[UMAX:%.*]] = call i64 @llvm.umax.i64(i64 [[TMP2]], i64 1)
+; CHECK-NEXT: [[BOUND:%.*]] = ashr exact i64 [[X:%.*]], 4
+; CHECK-NEXT: [[UMAX:%.*]] = call i64 @llvm.umax.i64(i64 [[BOUND]], i64 1)
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
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