Files
llvm/test/Transforms/InstCombine
Mikhail Maltsev faeea2dc5e [Analysis] Don't assume that unsigned overflow can't happen in EmitGEPOffset (PR42699)
Summary:
Currently when computing a GEP offset using the function EmitGEPOffset
for the following instruction

  getelementptr inbounds i32, i32* %p, i64 %offs

we get

  mul nuw i64 %offs, 4

Unfortunately we cannot assume that unsigned wrapping won't happen
here because %offs is allowed to be negative.

Making such assumptions can lead to miscompilations: see the new test
test24_neg_offs in InstCombine/icmp.ll. Without the patch InstCombine
would generate the following comparison:

   icmp eq i64 %offs, 4611686018427387902; 0x3ffffffffffffffe

Whereas the correct value to compare with is -2.

This patch replaces the NUW flag with NSW in the multiplication
instructions generated by EmitGEPOffset and adjusts the test suite.

https://bugs.llvm.org/show_bug.cgi?id=42699

Reviewers: chandlerc, craig.topper, ostannard, lebedev.ri, spatel, efriedma, nlopes, aqjune

Reviewed By: lebedev.ri

Subscribers: reames, lebedev.ri, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68342

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375089 91177308-0d34-0410-b5e6-96231b3b80d8
2019-10-17 08:59:06 +00:00
..
2019-09-26 19:01:18 +00:00
2019-08-14 16:50:06 +00:00
2019-09-11 10:51:26 +00:00
2019-09-06 16:26:59 +00:00
2019-06-21 17:51:18 +00:00

This directory contains test cases for the instcombine transformation.  The
dated tests are actual bug tests, whereas the named tests are used to test
for features that the this pass should be capable of performing.