Thumb1 load/store optimizer: Improve code to materialize new base register.
There are two add-immediate instructions in Thumb1: tADDi8 and tADDi3. Only
the latter supports using different source and destination registers, so
whenever we materialize a new base register (at a certain offset) we'd do
so by moving the base register value to the new register and then adding in
place. This patch changes the code to use a single tADDi3 if the offset is
small enough to fit in 3 bits.
Differential Revision: http://reviews.llvm.org/D5006
llvm-svn: 216193
diff --git a/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp b/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
index dc8cafa..9dc74a1 100644
--- a/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
+++ b/llvm/lib/Target/ARM/ARMLoadStoreOptimizer.cpp
@@ -360,13 +360,15 @@
int BaseOpc =
isThumb2 ? ARM::t2ADDri :
+ (isThumb1 && Offset < 8) ? ARM::tADDi3 :
isThumb1 ? ARM::tADDi8 : ARM::ADDri;
if (Offset < 0) {
+ Offset = - Offset;
BaseOpc =
isThumb2 ? ARM::t2SUBri :
+ (isThumb1 && Offset < 8) ? ARM::tSUBi3 :
isThumb1 ? ARM::tSUBi8 : ARM::SUBri;
- Offset = - Offset;
}
if (!TL->isLegalAddImmediate(Offset))
@@ -374,22 +376,28 @@
return false; // Probably not worth it then.
if (isThumb1) {
- if (Base != NewBase) {
+ // Thumb1: depending on immediate size, use either
+ // ADD NewBase, Base, #imm3
+ // or
+ // MOV NewBase, Base
+ // ADD NewBase, #imm8.
+ if (Base != NewBase && Offset >= 8) {
// Need to insert a MOV to the new base first.
- // FIXME: If the immediate fits in 3 bits, use ADD instead.
BuildMI(MBB, MBBI, dl, TII->get(ARM::tMOVr), NewBase)
.addReg(Base, getKillRegState(BaseKill))
.addImm(Pred).addReg(PredReg);
+ // Set up BaseKill and Base correctly to insert the ADDS/SUBS below.
+ Base = NewBase;
+ BaseKill = false;
}
AddDefaultT1CC(BuildMI(MBB, MBBI, dl, TII->get(BaseOpc), NewBase))
- .addReg(NewBase, getKillRegState(true)).addImm(Offset)
+ .addReg(Base, getKillRegState(BaseKill)).addImm(Offset)
.addImm(Pred).addReg(PredReg);
} else {
BuildMI(MBB, MBBI, dl, TII->get(BaseOpc), NewBase)
.addReg(Base, getKillRegState(BaseKill)).addImm(Offset)
.addImm(Pred).addReg(PredReg).addReg(0);
}
-
Base = NewBase;
BaseKill = true; // New base is always killed straight away.
}