This patch replaces all dominated uses of condition with true/false to
improve context-sensitive optimizations. It eliminates a bunch of
branches in llvm-opt-benchmark.
As a side effect, it may introduce new phi nodes in some corner cases.
See the following case:
```
define i1 @test(i1 %cmp, i1 %cond) {
entry:
br i1 %cond, label %bb1, label %bb2
bb1:
br i1 %cmp, label %if.then, label %if.else
if.then:
br %bb2
if.else:
br %bb2
bb2:
%res = phi i1 [%cmp, %entry], [%cmp, %if.then], [%cmp, %if.else]
ret i1 %res
}
```
It will be simplified into:
```
define i1 @test(i1 %cmp, i1 %cond) {
entry:
br i1 %cond, label %bb1, label %bb2
bb1:
br i1 %cmp, label %if.then, label %if.else
if.then:
br %bb2
if.else:
br %bb2
bb2:
%res = phi i1 [%cmp, %entry], [true, %if.then], [false, %if.else]
ret i1 %res
}
```
I am planning to fix this in late pipeline/CGP since this problem exists
before the patch.
As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
llvm-svn: 358546
This patch is based on the llvm-dev discussion here:
http://lists.llvm.org/pipermail/llvm-dev/2017-January/109631.html
Folding to i1 should always be desirable because that's better for value tracking
and we have special folds for i1 types.
I checked for other users of shouldChangeType() where this might have an effect,
but we already handle the i1 case differently than other types in all of those cases.
Side note: the default datalayout includes i1, so it seems we only find this gap in
shouldChangeType + phi folding for the case when there is (1) an explicit datalayout
without i1, (2) casting to i1 from a legal type, and (3) a phi with exactly 2 incoming
casted operands (as Björn mentioned).
Differential Revision: https://reviews.llvm.org/D29336
llvm-svn: 294066
