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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - SCEV: missed canonicalization ((-1 * (0 smin %n)) + %n) is actually just (0 smax %n)"
href="https://bugs.llvm.org/show_bug.cgi?id=46939">46939</a>
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<th>Summary</th>
<td>SCEV: missed canonicalization ((-1 * (0 smin %n)) + %n) is actually just (0 smax %n)
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</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Global Analyses
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>lebedev.ri@gmail.com
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</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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</tr></table>
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<div>
<pre>I'm not really sure how SCEV canonicalization is performed, but
<a href="https://rise4fun.com/Alive/GsleR">https://rise4fun.com/Alive/GsleR</a>
; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
; FIXME: ((-1 * (0 smin %n)) + %n) is actually just (0 smax %n)
declare void @iteration()
define void @reverse_loop(i32 %n) {
; CHECK-LABEL: 'reverse_loop'
; CHECK-NEXT: Classifying expressions for: @reverse_loop
; CHECK-NEXT: %i.011 = phi i32 [ %n, %for.body.lr.ph ], [ %dec, %for.body ]
; CHECK-NEXT: --> {%n,+,-1}<nsw><%for.body> U: full-set S: full-set Exits:
(0 smin %n) LoopDispositions: { %for.body: Computable }
; CHECK-NEXT: %dec = add nsw i32 %i.011, -1
; CHECK-NEXT: --> {(-1 + %n),+,-1}<nw><%for.body> U: full-set S: full-set
Exits: (-1 + (0 smin %n)) LoopDispositions: { %for.body: Computable }
; CHECK-NEXT: Determining loop execution counts for: @reverse_loop
; CHECK-NEXT: Loop %for.body: backedge-taken count is ((-1 * (0 smin %n)) +
%n)
; CHECK-NEXT: Loop %for.body: max backedge-taken count is 2147483647
; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is ((-1 * (0
smin %n)) + %n)
; CHECK-NEXT: Predicates:
; CHECK: Loop %for.body: Trip multiple is 1
;
entry:
%cmp10 = icmp sgt i32 %n, -1
br i1 %cmp10, label %for.body.lr.ph, label %for.cond.cleanup
for.body.lr.ph:
br label %for.body
for.body:
%i.011 = phi i32 [ %n, %for.body.lr.ph ], [ %dec, %for.body ]
call void @iteration()
%dec = add nsw i32 %i.011, -1
%cmp = icmp sgt i32 %i.011, 0
br i1 %cmp, label %for.body, label %for.cond.cleanup.loopexit
for.cond.cleanup.loopexit:
br label %for.cond.cleanup
for.cond.cleanup:
ret void
}</pre>
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