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[HashRecognize] Tighten pre-conditions for analysis #144757

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Merged
merged 3 commits into from
Jun 18, 2025
Merged

[HashRecognize] Tighten pre-conditions for analysis #144757

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86904ee
[HashRecognize] Tighten pre-conditions for analysis
artagnon Jun 18, 2025
61296b6
[HashRecognize] Add test with multiple blocks
artagnon Jun 18, 2025
982f8d8
[HashRecognize] Add test for TC % 8 != 0
artagnon Jun 18, 2025
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8 changes: 4 additions & 4 deletions llvm/lib/Analysis/HashRecognize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -561,14 +561,14 @@ std::variant<PolynomialInfo, ErrBits, StringRef>
HashRecognize::recognizeCRC() const {
if (!L.isInnermost())
return "Loop is not innermost";
unsigned TC = SE.getSmallConstantMaxTripCount(&L);
if (!TC || TC > 256)
return "Unable to find a small constant trip count";
BasicBlock *Latch = L.getLoopLatch();
BasicBlock *Exit = L.getExitBlock();
const PHINode *IndVar = L.getCanonicalInductionVariable();
if (!Latch || !Exit || !IndVar)
if (!Latch || !Exit || !IndVar || L.getNumBlocks() != 1)
return "Loop not in canonical form";
unsigned TC = SE.getSmallConstantTripCount(&L);
if (!TC || TC > 256 || TC % 8)
return "Unable to find a small constant byte-multiple trip count";

auto R = getRecurrences(Latch, IndVar, L);
if (!R)
Expand Down
62 changes: 57 additions & 5 deletions llvm/test/Analysis/HashRecognize/cyclic-redundancy-check.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -384,7 +384,7 @@ exit: ; preds = %loop
define i16 @not.crc.non.const.tc(i16 %crc.init, i32 %loop.limit) {
; CHECK-LABEL: 'not.crc.non.const.tc'
; CHECK-NEXT: Did not find a hash algorithm
; CHECK-NEXT: Reason: Unable to find a small constant trip count
; CHECK-NEXT: Reason: Unable to find a small constant byte-multiple trip count
;
entry:
br label %loop
Expand All @@ -404,8 +404,31 @@ exit: ; preds = %loop
ret i16 %crc.next
}

define i16 @not.crc.non.canonical.loop(i16 %crc.init) {
; CHECK-LABEL: 'not.crc.non.canonical.loop'
define i16 @not.crc.non.canonical.not.multiple.8(i16 %crc.init) {
; CHECK-LABEL: 'not.crc.non.canonical.not.multiple.8'
; CHECK-NEXT: Did not find a hash algorithm
; CHECK-NEXT: Reason: Unable to find a small constant byte-multiple trip count
;
entry:
br label %loop

loop: ; preds = %loop, %entry
%iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
%crc = phi i16 [ %crc.init, %entry ], [ %crc.next, %loop ]
%crc.shl = shl i16 %crc, 1
%crc.xor = xor i16 %crc.shl, 4129
%check.sb = icmp slt i16 %crc, 0
%crc.next = select i1 %check.sb, i16 %crc.xor, i16 %crc.shl
%iv.next = add nuw nsw i32 %iv, 1
%exit.cond = icmp samesign eq i32 %iv, 3
br i1 %exit.cond, label %exit, label %loop

exit: ; preds = %loop
ret i16 %crc.next
}

define i16 @not.crc.non.canonical.loop.countdown(i16 %crc.init) {
; CHECK-LABEL: 'not.crc.non.canonical.loop.countdown'
; CHECK-NEXT: Did not find a hash algorithm
; CHECK-NEXT: Reason: Loop not in canonical form
;
Expand All @@ -427,10 +450,39 @@ exit: ; preds = %loop
ret i16 %crc.next
}

define i16 @not.crc.non.canonical.loop.multiple.blocks(i16 %crc.init) {
; CHECK-LABEL: 'not.crc.non.canonical.loop.multiple.blocks'
; CHECK-NEXT: Did not find a hash algorithm
; CHECK-NEXT: Reason: Loop not in canonical form
;
entry:
br label %loop

loop: ; preds = %loop, %entry
%iv = phi i32 [ 0, %entry ], [ %iv.next, %continue ]
%crc = phi i16 [ %crc.init, %entry ], [ %crc.next, %continue ]
%check.sb = icmp slt i16 %crc, 0
%crc.shl = shl i16 %crc, 1
br i1 %check.sb, label %xor, label %continue

xor:
%crc.xor = xor i16 %crc.shl, 4129
br label %continue

continue:
%crc.next = phi i16 [ %crc.xor, %xor ], [ %crc.shl, %loop ]
%iv.next = add nuw nsw i32 %iv, 1
%exit.cond = icmp samesign eq i32 %iv, 7
br i1 %exit.cond, label %exit, label %loop

exit: ; preds = %loop
ret i16 %crc.next
}

define i16 @not.crc.tc.limit(i16 %crc.init) {
; CHECK-LABEL: 'not.crc.tc.limit'
; CHECK-NEXT: Did not find a hash algorithm
; CHECK-NEXT: Reason: Unable to find a small constant trip count
; CHECK-NEXT: Reason: Unable to find a small constant byte-multiple trip count
;
entry:
br label %loop
Expand Down Expand Up @@ -617,7 +669,7 @@ loop: ; preds = %loop, %entry
%crc.xor = xor i16 %crc.lshr, -24575
%crc.next = select i1 %check.sb, i16 %crc.lshr, i16 %crc.xor
%iv.next = add nuw nsw i8 %iv, 1
%exit.cond = icmp samesign ult i8 %iv, 20
%exit.cond = icmp samesign ult i8 %iv, 31
br i1 %exit.cond, label %loop, label %exit

exit: ; preds = %loop
Expand Down
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