Taking too long to build a huge file

[llvmbot]

Bugzilla Link	28649
Version	trunk
OS	Linux
Blocks	#24719
Attachments	test case, small.c
Reporter	LLVM Bugzilla Contributor
CC	@lalozano

Extended Description

It seems to take an infinite long time to do this:

$ clang -cc1 -triple thumbv7-linux-gnueabi -emit-obj -x c huge.c

while it "only" takes 2 minutes for armv7 and x86_64. If invoked in this way, it only took ~1 minute:

$ clang -target thumbv7-linux-gnueabi -c -o huge.o -x c huge.c

[llvmbot]

TL;DR selectiondag reassociate and combining

I can only reproduce it at O0.

[llvmbot]

The original source code is written to stress i-tlb. With O1 and O2, the compiler optimizes everything away before the pass.

The upstream bug is here:
https://bugs.chromium.org/p/chromium/issues/detail?id=630443