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release/20.x: [SCEV] Use ashr to adjust constant multipliers (#135534) #135543

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Merged
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Apr 14, 2025
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release/20.x: [SCEV] Use ashr to adjust constant multipliers (#135534) #135543

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2 changes: 1 addition & 1 deletion llvm/lib/Analysis/ScalarEvolution.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7854,7 +7854,7 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
unsigned GCD = std::min(MulZeros, TZ);
APInt DivAmt = APInt::getOneBitSet(BitWidth, TZ - GCD);
SmallVector<const SCEV*, 4> MulOps;
MulOps.push_back(getConstant(OpC->getAPInt().lshr(GCD)));
MulOps.push_back(getConstant(OpC->getAPInt().ashr(GCD)));
append_range(MulOps, LHSMul->operands().drop_front());
auto *NewMul = getMulExpr(MulOps, LHSMul->getNoWrapFlags());
ShiftedLHS = getUDivExpr(NewMul, getConstant(DivAmt));
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19 changes: 19 additions & 0 deletions llvm/test/Analysis/ScalarEvolution/pr135531.ll
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@@ -0,0 +1,19 @@
; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 5
; RUN: opt -disable-output -passes='print<scalar-evolution>' < %s 2>&1 | FileCheck %s

define i32 @pr135511(i32 %x) {
; CHECK-LABEL: 'pr135511'
; CHECK-NEXT: Classifying expressions for: @pr135511
; CHECK-NEXT: %and = and i32 %x, 16382
; CHECK-NEXT: --> (2 * (zext i13 (trunc i32 (%x /u 2) to i13) to i32))<nuw><nsw> U: [0,16383) S: [0,16383)
; CHECK-NEXT: %neg = sub nsw i32 0, %and
; CHECK-NEXT: --> (-2 * (zext i13 (trunc i32 (%x /u 2) to i13) to i32))<nsw> U: [0,-1) S: [-16382,1)
; CHECK-NEXT: %res = and i32 %neg, 268431360
; CHECK-NEXT: --> (4096 * (zext i16 (trunc i32 ((-1 * (zext i13 (trunc i32 (%x /u 2) to i13) to i32))<nsw> /u 2048) to i16) to i32))<nuw><nsw> U: [0,268431361) S: [0,268431361)
; CHECK-NEXT: Determining loop execution counts for: @pr135511
;
%and = and i32 %x, 16382
%neg = sub nsw i32 0, %and
%res = and i32 %neg, 268431360
ret i32 %res
}
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