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[DA] Add tests for GCD MIV misses dependency due to overflow (NFC) #169926

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Merged
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Dec 1, 2025
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[DA] Add tests for GCD MIV misses dependency due to overflow (NFC) #169926

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119 changes: 119 additions & 0 deletions llvm/test/Analysis/DependenceAnalysis/gcd-miv-overflow.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,125 @@ loop:
%ec = icmp eq i64 %i.inc, 100
br i1 %ec, label %exit, label %loop

exit:
ret void
}

; max_i = INT64_MAX/6 // 1537228672809129301
; for (long long i = 0; i <= max_i; i++) {
; A[-6*i + INT64_MAX] = 0;
; if (i)
; A[3*i - 2] = 1;
; }
;
; FIXME: DependenceAnalysis currently detects no dependency between the two
; stores, but it does exist. For example,
;
; memory access | i == 1 | i == (max_i + 1) / 2 | i == max_i
; ---------------------|--------|----------------------|-------------------
; A[-6*i + INT64_MAX] | | A[3*max_i - 2] | A[1]
; A[3*i - 2] | A[1] | | A[3*max_i - 2]
;
;
define void @gcdmiv_delta_ovfl(ptr %A) {
; CHECK-ALL-LABEL: 'gcdmiv_delta_ovfl'
; CHECK-ALL-NEXT: Src: store i8 0, ptr %idx.0, align 1 --> Dst: store i8 0, ptr %idx.0, align 1
; CHECK-ALL-NEXT: da analyze - none!
; CHECK-ALL-NEXT: Src: store i8 0, ptr %idx.0, align 1 --> Dst: store i8 1, ptr %idx.1, align 1
; CHECK-ALL-NEXT: da analyze - none!
; CHECK-ALL-NEXT: Src: store i8 1, ptr %idx.1, align 1 --> Dst: store i8 1, ptr %idx.1, align 1
; CHECK-ALL-NEXT: da analyze - none!
;
; CHECK-GCD-MIV-LABEL: 'gcdmiv_delta_ovfl'
; CHECK-GCD-MIV-NEXT: Src: store i8 0, ptr %idx.0, align 1 --> Dst: store i8 0, ptr %idx.0, align 1
; CHECK-GCD-MIV-NEXT: da analyze - consistent output [*]!
; CHECK-GCD-MIV-NEXT: Src: store i8 0, ptr %idx.0, align 1 --> Dst: store i8 1, ptr %idx.1, align 1
; CHECK-GCD-MIV-NEXT: da analyze - none!
; CHECK-GCD-MIV-NEXT: Src: store i8 1, ptr %idx.1, align 1 --> Dst: store i8 1, ptr %idx.1, align 1
; CHECK-GCD-MIV-NEXT: da analyze - consistent output [*]!
;
entry:
br label %loop.header

loop.header:
%i = phi i64 [ 0, %entry ], [ %i.inc, %loop.latch ]
%subscript.0 = phi i64 [ 9223372036854775807, %entry ], [ %subscript.0.next, %loop.latch ]
%subscript.1 = phi i64 [ -2, %entry ], [ %subscript.1.next, %loop.latch ]
%idx.0 = getelementptr inbounds i8, ptr %A, i64 %subscript.0
store i8 0, ptr %idx.0
%cond.store = icmp ne i64 %i, 0
br i1 %cond.store, label %if.store, label %loop.latch

if.store:
%idx.1 = getelementptr i8, ptr %A, i64 %subscript.1
store i8 1, ptr %idx.1
br label %loop.latch

loop.latch:
%i.inc = add nuw nsw i64 %i, 1
%subscript.0.next = add nsw i64 %subscript.0, -6
%subscript.1.next = add nsw i64 %subscript.1, 3
%exitcond = icmp sgt i64 %i.inc, 1537228672809129301
br i1 %exitcond, label %exit, label %loop.header

exit:
ret void
}

; max_i = INT64_MAX/3 // 3074457345618258602
; for (i = 0; i < max_i; i++) {
; A[3*i] = 0;
; 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
; effectively `-3*i + (INT64_MAX - 1)`. Thus, accesses will be as follows:
;
; memory access | i == 1 | i == max_i - 1
; ---------------------------|------------------|------------------
; A[3*i] | A[3] | A[INT64_MAX - 4]
; A[-3*i - 3*m - INT64_MAX] | A[INT64_MAX - 4] | A[3]
;

define void @gcdmiv_const_ovfl(ptr %A, i64 %m) {
; CHECK-ALL-LABEL: 'gcdmiv_const_ovfl'
; 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: Src: store i8 1, ptr %gep.1, align 1 --> Dst: store i8 1, ptr %gep.1, align 1
; CHECK-ALL-NEXT: da analyze - none!
;
; CHECK-GCD-MIV-LABEL: 'gcdmiv_const_ovfl'
; 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: 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 [*]!
;
entry:
%m.3 = mul nsw i64 -3, %m
%const = sub i64 %m.3, 9223372036854775807
%guard = icmp ne i64 %const, 0
br i1 %guard, label %loop, label %exit
Comment on lines +161 to +162
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@kasuga-fj kasuga-fj Nov 29, 2025

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This is a hack to transfer the nsw flag of 3 * %m from IR to SCEV. Please let me know if there is a better way to do this.


loop:
%i = phi i64 [ 0, %entry ], [ %i.inc, %loop ]
%offset.0 = phi i64 [ 0, %entry ], [ %offset.0.next, %loop ]
%offset.1 = phi i64 [ %const, %entry ], [ %offset.1.next, %loop ]
%gep.0 = getelementptr inbounds i8, ptr %A, i64 %offset.0
%gep.1 = getelementptr inbounds i8, ptr %A, i64 %offset.1
store i8 0, ptr %gep.0
store i8 1, ptr %gep.1
%i.inc = add nuw nsw i64 %i, 1
%offset.0.next = add nsw i64 %offset.0, 3
%offset.1.next = add nsw i64 %offset.1, -3
%ec = icmp eq i64 %i.inc, 3074457345618258602
br i1 %ec, label %exit, label %loop

exit:
ret void
}
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