Teach the function cloner (and thus the inliner) to simplify PHINodes

aggressively. There are lots of dire warnings about this being expensive
that seem to predate switching to the TrackingVH-based value remapper
that is automatically updated on RAUW. This makes it easy to not just
prune single-entry PHIs, but to fully simplify PHIs, and to recursively
simplify the newly inlined code to propagate PHINode simplifications.

This introduces a bit of a thorny problem though. We may end up
simplifying a branch condition to a constant when we fold PHINodes, and
we would like to nuke any dead blocks resulting from this so that time
isn't wasted continually analyzing them, but this isn't easy. Deleting
basic blocks *after* they are fully cloned and mapped into the new
function currently requires manually updating the value map. The last
piece of the simplification-during-inlining puzzle will require either
switching to WeakVH mappings or some other piece of refactoring. I've
left a FIXME in the testcase about this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153410 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 33 insertions, 3 deletions

diff --git a/test/Transforms/Inline/inline_cleanup.ll b/test/Transforms/Inline/inline_cleanup.ll
index 7583dddea9..cf57cf0641 100644
--- a/test/Transforms/Inline/inline_cleanup.ll
+++ b/test/Transforms/Inline/inline_cleanup.ll
@@ -74,7 +74,7 @@ entry:
 
 declare void @f(i32 %x)
 
-define void @inner2(i32 %x, i32 %y, i32 %z) {
+define void @inner2(i32 %x, i32 %y, i32 %z, i1 %b) {
 entry:
   %cmp1 = icmp ne i32 %x, 0
   br i1 %cmp1, label %then1, label %end1
@@ -102,17 +102,47 @@ then3:
   br label %end3
 
 end3:
+  br i1 %b, label %end3.1, label %end3.2
+
+end3.1:
+  %x3.1 = or i32 %x, 10
+  br label %end3.3
+
+end3.2:
+  %x3.2 = or i32 %x, 10
+  br label %end3.3
+
+end3.3:
+  %x3.3 = phi i32 [ %x3.1, %end3.1 ], [ %x3.2, %end3.2 ]
+  %cmp4 = icmp slt i32 %x3.3, 1
+  br i1 %cmp4, label %then4, label %end4
+
+then4:
+  call void @f(i32 %x3.3)
+  br label %end4
+
+end4:
   ret void
 }
 
-define void @outer2(i32 %z) {
+define void @outer2(i32 %z, i1 %b) {
 ; Ensure that after inlining, none of the blocks with a call to @f actually
 ; make it through inlining.
 ; CHECK: define void @outer2
 ; CHECK-NOT: call
+;
+; FIXME: Currently, we aren't smart enough to delete the last dead basic block.
+; However, we do make the condition a constant. Check that at least until we can
+; start removing the block itself.
+; CHECK: br i1 false, label %[[LABEL:[a-z0-9_.]+]],
+; CHECK-NOT: call
+; CHECK: [[LABEL]]:
+; CHECK-NEXT: call void @f(i32 10)
+; CHECK-NOT: call
+;
 ; CHECK: ret void
 
 entry:
-  call void @inner2(i32 0, i32 -1, i32 %z)
+  call void @inner2(i32 0, i32 -1, i32 %z, i1 %b)
   ret void
 }