Summary:
The BranchFolding pass is currently missing opportunities to hoist
common code if the hoisted-to block contains a single conditional branch
that has register uses. This occurs somewhat frequently on AArch64 with
CBZ/TBZ opcodes.
This change also eliminates some code differences when debug info is
present since the presence of e.g. DBG_VALUE instructions in the
hoisted-to block can enable hoisting that wouldn't have occurred without
them.
Reviewers: MatzeB, rnk, kparzysz, twoh, aprantl, javed.absar
Subscribers: kristof.beyls, JDevlieghere, mcrosier, llvm-commits
Differential Revision: https://reviews.llvm.org/D46324
llvm-svn: 332265
if (Uses.empty())
return Loc;
+ // If the terminator is the only instruction in the block and Uses is not
+ // empty (or we would have returned above), we can still safely hoist
+ // instructions just before the terminator as long as the Defs/Uses are not
+ // violated (which is checked in HoistCommonCodeInSuccs).
if (Loc == MBB->begin())
- return MBB->end();
+ return Loc;
// The terminator is probably a conditional branch, try not to separate the
// branch from condition setting instruction.
--- /dev/null
+# RUN: llc -o - %s -mtriple=aarch64 -run-pass branch-folder | FileCheck %s
+# Check that BranchFolding pass is able to hoist a common instruction into a block with a single branch instruction.
+name: func
+tracksRegLiveness: true
+body: |
+ bb.0:
+ ; CHECK-LABEL: name: func
+ ; CHECK-LABEL: bb.0:
+ ; CHECK: $x0 = ADDXri $x0, 1, 0
+ ; CHECK: CBZX $x1, %bb.2
+ liveins: $x1
+ CBZX $x1, %bb.2
+
+ bb.1:
+ ; CHECK-LABEL: bb.1:
+ ; CHECK-NOT: $x0 = ADDXri $x0, 1, 0
+ liveins: $x0
+ $x0 = ADDXri $x0, 1, 0
+ $x0 = ADDXri $x0, 2, 0
+ RET_ReallyLR implicit $x0
+
+ bb.2:
+ ; CHECK-LABEL: bb.2:
+ ; CHECK-NOT: $x0 = ADDXri $x0, 1, 0
+ liveins: $x0
+ $x0 = ADDXri $x0, 1, 0
+ $x0 = ADDXri $x0, 3, 0
+ RET_ReallyLR implicit $x0
+...