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Roman Lebedev 473a063a5e [InstCombine] Fold '((%x * %y) u/ %x) != %y' to '@llvm.umul.with.overflow' + overflow bit extraction 
Summary:
`((%x * %y) u/ %x) != %y` is one of (3?) common ways to check that
some unsigned multiplication (will not) overflow.
Currently, we don't catch it. We could:
```
$ /repositories/alive2/build-Clang-unknown/alive -root-only ~/llvm-patch1.ll
Processing /home/lebedevri/llvm-patch1.ll..

----------------------------------------
Name: no overflow
  %o0 = mul i4 %y, %x
  %o1 = udiv i4 %o0, %x
  %r = icmp ne i4 %o1, %y
  ret i1 %r
=>
  %n0 = umul_overflow i4 %x, %y
  %o0 = extractvalue {i4, i1} %n0, 0
  %o1 = udiv %o0, %x
  %r = extractvalue {i4, i1} %n0, 1
  ret %r

Done: 1
Optimization is correct!

----------------------------------------
Name: no overflow
  %o0 = mul i4 %y, %x
  %o1 = udiv i4 %o0, %x
  %r = icmp eq i4 %o1, %y
  ret i1 %r
=>
  %n0 = umul_overflow i4 %x, %y
  %o0 = extractvalue {i4, i1} %n0, 0
  %o1 = udiv %o0, %x
  %n1 = extractvalue {i4, i1} %n0, 1
  %r = xor %n1, -1
  ret i1 %r

Done: 1
Optimization is correct!

```

Reviewers: nikic, spatel, efriedma, xbolva00, RKSimon

Reviewed By: nikic

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65144

llvm-svn: 370348
 		2019-08-29 12:47:20 +00:00
clang Fix variable ‘IsInitCapturePack’ set but not used warning. NFCI. 2019-08-29 12:41:19 +00:00
clang-tools-extra Fix MSVC "not all control paths return a value" warning. NFCI. 2019-08-29 12:37:02 +00:00
compiler-rt [sanitizer] Support monorepo layout in symbolizer build script 2019-08-29 02:02:03 +00:00
debuginfo-tests Make nrvo-string test more robust. 2019-06-27 20:38:37 +00:00
libclc Revert "Rename F_{None,Text,Append} to OF_{None,Text,Append}. NFC" 2019-08-05 17:23:23 +00:00
libcxx [libc++] Fix visibility of __vector_base_common on GCC 2019-08-28 18:10:39 +00:00
libcxxabi Provide a meaningful diagnostic when LLVM_PATH doesn't point to a directory 2019-08-19 23:51:26 +00:00
libunwind [runtimes] Don't depend on libpthread on Android 2019-07-22 20:41:03 +00:00
lld lld: Make a test not fail if "repro" is part of the build directory name 2019-08-28 14:33:35 +00:00
lldb [lldb][NFC] Try fixing TestCompletion.py on Windows 2019-08-29 09:57:02 +00:00
llgo IR: Support parsing numeric block ids, and emit them in textual output. 2019-03-22 18:27:13 +00:00
llvm [InstCombine] Fold '((%x * %y) u/ %x) != %y' to '@llvm.umul.with.overflow' + overflow bit extraction 2019-08-29 12:47:20 +00:00
openmp Use target_impl functions to replace more inline asm 2019-08-28 15:04:06 +00:00
parallel-libs Fix typos throughout the license files that somehow I and my reviewers 2019-01-21 09:52:34 +00:00
polly [ScopBuilder] Simplify main statement flag in buildEqivClassBlockStmts. NFC. 2019-08-26 21:31:47 +00:00
pstl [pstl] Allow customizing whether per-TU insulation is provided 2019-08-13 12:49:00 +00:00
.arcconfig Update monorepo .arcconfig with new project callsign. 2019-01-31 14:34:59 +00:00
.clang-format Add .clang-tidy and .clang-format files to the toplevel of the 2019-01-29 16:43:16 +00:00
.clang-tidy Disable tidy checks with too many hits 2019-02-01 11:20:13 +00:00
.gitignore Change /build to /build* in top-level .gitignore. 2019-08-02 02:14:08 +00:00
README.md
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README.md

The LLVM Compiler Infrastructure

This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments.