https://llvm.org/bugs/show_bug.cgi?id=28922
Bug ID: 28922
Summary: Unsigned wrap check conditions falling to original
code
Product: Polly
Version: unspecified
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Optimizer
Assignee: polly-...@googlegroups.com
Reporter: chr...@codeaurora.org
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Created attachment 16927
--> https://llvm.org/bugs/attachment.cgi?id=16927&action=edit
test case
> opt -polly-process-unprofitable -polly-code-generator=isl -polly-ast
> -analyze test.ll
Consider the context check below,
:: isl ast :: foo4 :: %entry.split---%for.cond.cleanup
if (1 && 0 == (m >= n + 9223372036854775809 || n >= m + 9223372036854775808 ||
m == -9223372036854775808))
for (int c0 = 0; c0 < -m + n; c0 += 1)
Stmt_for_body(c0);
else
{ /* original code */ }
Values 9223372036854775809 (0x8000000000000001) and 9223372036854775808
(8000000000000000) are already overflown and having addition operation with
them leads to the result being wrapped.
Hence this would lead to the context condition falling to the original code. On
the other hand, say if the condition were in form where there was no operation
with the max int values it would not wrap. i.e. if the condition were like (m -
n >= 9223372036854775809) or (n - m >= 9223372036854775808).
> opt -polly-process-unprofitable -polly-code-generator=isl -polly-codegen -S
> test.ll
--snip--
polly.split_new_and_old: ; preds = %entry
%0 = call { i64, i1 } @llvm.sadd.with.overflow.i64(i64 %n, i64
-9223372036854775807) <===
%.obit = extractvalue { i64, i1 } %0, 1
%polly.overflow.state = or i1 false, %.obit
%.res = extractvalue { i64, i1 } %0, 0
%1 = icmp sge i64 %m, %.res
%2 = call { i64, i1 } @llvm.sadd.with.overflow.i64(i64 %m, i64
-9223372036854775808) <===
%.obit1 = extractvalue { i64, i1 } %2, 1
%polly.overflow.state2 = or i1 %polly.overflow.state, %.obit1
%.res3 = extractvalue { i64, i1 } %2, 0
%3 = icmp sge i64 %n, %.res3
%4 = or i1 %1, %3
%5 = icmp eq i64 %m, -9223372036854775808
%6 = or i1 %4, %5
%7 = sext i1 %6 to i64
%8 = icmp eq i64 0, %7
%9 = and i1 true, %8
%polly.rtc.overflown = xor i1 %polly.overflow.state2, true
%polly.rtc.result = and i1 %9, %polly.rtc.overflown
br i1 %polly.rtc.result, label %polly.start, label %entry.split
--snip--
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