Change Thumb2 jumptable codegen to one that uses two level jumps:
Before:
adr r12, #LJTI3_0_0
ldr pc, [r12, +r0, lsl #2]
LJTI3_0_0:
.long LBB3_24
.long LBB3_30
.long LBB3_31
.long LBB3_32
After:
adr r12, #LJTI3_0_0
add pc, r12, +r0, lsl #2
LJTI3_0_0:
b.w LBB3_24
b.w LBB3_30
b.w LBB3_31
b.w LBB3_32
This has several advantages.
1. This will make it easier to optimize this to a TBB / TBH instruction +
(smaller) table.
2. This eliminate the need for ugly asm printer hack to force the address
into thumb addresses (bit 0 is one).
3. Same codegen for pic and non-pic.
4. This eliminate the need to align the table so constantpool island pass
won't have to over-estimate the size.
Based on my calculation, the later is probably slightly faster as well since
ldr pc with shifter address is very slow. That is, it should be a win as long
as the HW implementation can do a reasonable job of branch predict the second
branch.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@77024 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/ARMConstantIslandPass.cpp b/lib/Target/ARM/ARMConstantIslandPass.cpp
index 48db39b..2465521 100644
--- a/lib/Target/ARM/ARMConstantIslandPass.cpp
+++ b/lib/Target/ARM/ARMConstantIslandPass.cpp
@@ -389,10 +389,7 @@
int UOpc = Opc;
switch (Opc) {
case ARM::tBR_JTr:
- case ARM::t2BR_JTr:
- case ARM::t2BR_JTm:
- case ARM::t2BR_JTadd:
- // A Thumb table jump may involve padding; for the offsets to
+ // A Thumb1 table jump may involve padding; for the offsets to
// be right, functions containing these must be 4-byte aligned.
AFI->setAlign(2U);
if ((Offset+MBBSize)%4 != 0)
@@ -787,10 +784,7 @@
// Thumb1 jump tables require padding. They should be at the end;
// following unconditional branches are removed by AnalyzeBranch.
MachineInstr *ThumbJTMI = prior(MBB->end());
- if (ThumbJTMI->getOpcode() == ARM::tBR_JTr ||
- ThumbJTMI->getOpcode() == ARM::t2BR_JTr ||
- ThumbJTMI->getOpcode() == ARM::t2BR_JTm ||
- ThumbJTMI->getOpcode() == ARM::t2BR_JTadd) {
+ if (ThumbJTMI->getOpcode() == ARM::tBR_JTr) {
unsigned newMIOffset = GetOffsetOf(ThumbJTMI);
unsigned oldMIOffset = newMIOffset - delta;
if (oldMIOffset%4 == 0 && newMIOffset%4 != 0) {