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llvm-project/llvm/test/Analysis/ScalarEvolution/pr27315.ll

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[SCEV] Don't always add no-wrap flags to post-inc add recs Fixes PR27315. The post-inc version of an add recurrence needs to "follow the same rules" as a normal add or subtract expression. Otherwise we miscompile programs like ``` int main() { int a = 0; unsigned a_u = 0; volatile long last_value; do { a_u += 3; last_value = (long) ((int) a_u); if (will_add_overflow(a, 3)) { // Leave, and don't actually do the increment, so no UB. printf("last_value = %ld\n", last_value); exit(0); } a += 3; } while (a != 46); return 0; } ``` This patch changes SCEV to put no-wrap flags on post-inc add recurrences only when the poison from a potential overflow will go ahead to cause undefined behavior. To avoid regressing performance too much, I've assumed infinite loops without side effects is undefined behavior to prove poison<->UB equivalence in more cases. This isn't ideal, but is not new to LLVM as a whole, and far better than the situation I'm trying to fix. llvm-svn: 271151
2016-05-29 08:32:17 +08:00
; RUN: opt -analyze -scalar-evolution < %s | FileCheck %s
declare i1 @use(i64)
define void @f_0() {
; CHECK-LABEL: Classifying expressions for: @f_0
; CHECK: %iv = phi i32 [ 0, %entry ], [ %iv.inc.nowrap, %be ]
; CHECK-NEXT: --> {0,+,1}<nuw><nsw><%loop>
; CHECK: %iv.inc.maywrap = add i32 %iv, 1
; CHECK-NEXT: --> {1,+,1}<nuw><%loop>
; CHECK: %iv.inc.maywrap.sext = sext i32 %iv.inc.maywrap to i64
; CHECK-NEXT: --> (sext i32 {1,+,1}<nuw><%loop> to i64)
entry:
br label %loop
loop:
%iv = phi i32 [ 0, %entry ], [ %iv.inc.nowrap, %be ]
%iv.inc.maywrap = add i32 %iv, 1
%iv.inc.maywrap.sext = sext i32 %iv.inc.maywrap to i64
%cond0 = call i1 @use(i64 %iv.inc.maywrap.sext)
br i1 %cond0, label %be, label %leave
be:
%iv.inc.nowrap = add nsw i32 %iv, 1
%be.cond = call i1 @use(i64 0) ;; Get an unanalyzable value
br i1 %be.cond, label %loop, label %leave
leave:
ret void
}