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[DA] Remove special handling for SCEVAddExpr in GCD MIV (#169927)

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In `gcdMIVtest`, there is logic that assumes the addition(s) of
`SCEVAddExpr` don't overflow without any checks. Adding overflow checks
would be fine, but this part appeart to be less useful. So this patch
removes it.

Fix one of the tests added in #169926.
This commit is contained in:
Ryotaro Kasuga
2025-12-01 23:34:10 +09:00
committed by GitHub
parent 235d44d8b6
commit fa6d611f0a
2 changed files with 4 additions and 23 deletions
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18
llvm/lib/Analysis/DependenceAnalysis.cpp
View File

@@ -2587,30 +2587,12 @@ bool DependenceInfo::gcdMIVtest(const SCEV *Src, const SCEV *Dst,
return false;
LLVM_DEBUG(dbgs() << " Delta = " << *Delta << "\n");
const SCEVConstant *Constant = dyn_cast<SCEVConstant>(Delta);
if (const SCEVAddExpr *Sum = dyn_cast<SCEVAddExpr>(Delta)) {
// If Delta is a sum of products, we may be able to make further progress.
for (const SCEV *Operand : Sum->operands()) {
if (isa<SCEVConstant>(Operand)) {
assert(!Constant && "Surprised to find multiple constants");
Constant = cast<SCEVConstant>(Operand);
} else if (const SCEVMulExpr *Product = dyn_cast<SCEVMulExpr>(Operand)) {
// Search for constant operand to participate in GCD;
// If none found; return false.
std::optional<APInt> ConstOp = getConstanCoefficient(Product);
if (!ConstOp)
return false;
ExtraGCD = APIntOps::GreatestCommonDivisor(ExtraGCD, ConstOp->abs());
} else
return false;
}
}
if (!Constant)
return false;
APInt ConstDelta = cast<SCEVConstant>(Constant)->getAPInt();
LLVM_DEBUG(dbgs() << " ConstDelta = " << ConstDelta << "\n");
if (ConstDelta == 0)
return false;
RunningGCD = APIntOps::GreatestCommonDivisor(RunningGCD, ExtraGCD);
LLVM_DEBUG(dbgs() << " RunningGCD = " << RunningGCD << "\n");
APInt Remainder = ConstDelta.srem(RunningGCD);
if (Remainder != 0) {

9
llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll
View File

@@ -127,9 +127,8 @@ exit:
; A[-3*i - 3*m - INT64_MAX] = 1;
; }
;
; FIXME: DependenceAnalysis currently detects no dependency between the two
; stores, but it may exist. For example, consider `m = 1`. Then,
; `-3*m - INT64_MAX` is `INT64_MAX - 1`. So `-3*i - 3*m - INT64_MAX` is
; Dependency may exist between the two stores. For example, consider `m = 1`.
; Then, `-3*m - INT64_MAX` is `INT64_MAX - 1`. So `-3*i - 3*m - INT64_MAX` is
; effectively `-3*i + (INT64_MAX - 1)`. Thus, accesses will be as follows:
;
; memory access | i == 1 | i == max_i - 1
@@ -143,7 +142,7 @@ define void @gcdmiv_const_ovfl(ptr %A, i64 %m) {
; CHECK-ALL-NEXT: Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 0, ptr %gep.0, align 1
; CHECK-ALL-NEXT: da analyze - none!
; CHECK-ALL-NEXT: Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 1, ptr %gep.1, align 1
; CHECK-ALL-NEXT: da analyze - none!
; CHECK-ALL-NEXT: da analyze - output [*|<]!
; CHECK-ALL-NEXT: Src: store i8 1, ptr %gep.1, align 1 --> Dst: store i8 1, ptr %gep.1, align 1
; CHECK-ALL-NEXT: da analyze - none!
;
@@ -151,7 +150,7 @@ define void @gcdmiv_const_ovfl(ptr %A, i64 %m) {
; CHECK-GCD-MIV-NEXT: Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 0, ptr %gep.0, align 1
; CHECK-GCD-MIV-NEXT: da analyze - consistent output [*]!
; CHECK-GCD-MIV-NEXT: Src: store i8 0, ptr %gep.0, align 1 --> Dst: store i8 1, ptr %gep.1, align 1
; CHECK-GCD-MIV-NEXT: da analyze - none!
; CHECK-GCD-MIV-NEXT: da analyze - consistent output [*|<]!
; CHECK-GCD-MIV-NEXT: Src: store i8 1, ptr %gep.1, align 1 --> Dst: store i8 1, ptr %gep.1, align 1
; CHECK-GCD-MIV-NEXT: da analyze - consistent output [*]!
;