Codegen: Tail-duplicate during placement.

The tail duplication pass uses an assumed layout when making duplication
decisions. This is fine, but passes up duplication opportunities that
may arise when blocks are outlined. Because we want the updated CFG to
affect subsequent placement decisions, this change must occur during
placement.

In order to achieve this goal, TailDuplicationPass is split into a
utility class, TailDuplicator, and the pass itself. The pass delegates
nearly everything to the TailDuplicator object, except for looping over
the blocks in a function. This allows the same code to be used for tail
duplication in both places.

This change, in concert with outlining optional branches, allows
triangle shaped code to perform much better, esepecially when the
taken/untaken branches are correlated, as it creates a second spine when
the tests are small enough.

Issue from previous rollback fixed, and a new test was added for that
case as well.

Differential revision: https://reviews.llvm.org/D18226

llvm-svn: 283274

1 files changed, 20 insertions, 2 deletions

diff --git a/llvm/test/CodeGen/X86/ragreedy-bug.ll b/llvm/test/CodeGen/X86/ragreedy-bug.ll
index e8426317f13..bfeb041f89a 100644
--- a/llvm/test/CodeGen/X86/ragreedy-bug.ll
+++ b/llvm/test/CodeGen/X86/ragreedy-bug.ll
@@ -3,16 +3,34 @@
 ; This testing case is reduced from 197.parser prune_match function.
 ; We make sure register copies are not generated on isupper.exit blocks.
 
-; CHECK: isupper.exit
+; isupper.exit and isupper.exit223 get tail-duplicated into all their
+; predecessors.
+; CHECK: cond.true.i.i
 ; CHECK-NEXT: in Loop
+; Mem-move
+; CHECK-NEXT: movl
+; CHECK-NEXT: andl
 ; CHECK-NEXT: testl
 ; CHECK-NEXT: jne
-; CHECK: isupper.exit
+; CHECK: cond.true.i.i217
 ; CHECK-NEXT: in Loop
+; Mem-move
+; CHECK-NEXT: movl
+; CHECK-NEXT: andl
 ; CHECK-NEXT: testl
 ; CHECK-NEXT: je
+; CHECK: cond.false.i.i
 ; CHECK: maskrune
+; CHECK-NEXT: movzbl
+; CHECK-NEXT: movzbl
+; CHECK-NEXT: testl
+; CHECK-NEXT: je
+; CHECK: cond.false.i.i219
 ; CHECK: maskrune
+; CHECK-NEXT: movzbl
+; CHECK-NEXT: movzbl
+; CHECK-NEXT: testl
+; CHECK-NEXT: jne
 
 %struct.List_o_links_struct = type { i32, i32, i32, %struct.List_o_links_struct* }
 %struct.Connector_struct = type { i16, i16, i8, i8, %struct.Connector_struct*, i8* }