Fold the PPCISD shifts when presented with 0 inputs. This occurs for code
like:
long long test(long long X, int Y) {
return 1ULL << Y;
}
long long test2(long long X, int Y) {
return -1LL << Y;
}
which we used to compile to:
_test:
li r2, 1
subfic r3, r5, 32
li r4, 0
addi r6, r5, -32
srw r3, r2, r3
slw r4, r4, r5
slw r6, r2, r6
or r3, r4, r3
slw r4, r2, r5
or r3, r3, r6
blr
_test2:
li r2, -1
subfic r3, r5, 32
addi r6, r5, -32
srw r3, r2, r3
slw r4, r2, r5
slw r2, r2, r6
or r3, r4, r3
or r3, r3, r2
blr
Now we produce:
_test:
li r2, 1
addi r3, r5, -32
subfic r4, r5, 32
slw r3, r2, r3
srw r4, r2, r4
or r3, r4, r3
slw r4, r2, r5
blr
_test2:
li r2, -1
subfic r3, r5, 32
addi r6, r5, -32
srw r3, r2, r3
slw r4, r2, r5
slw r2, r2, r6
or r3, r4, r3
or r3, r3, r2
blr
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@30479 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/PPCISelLowering.cpp b/lib/Target/PowerPC/PPCISelLowering.cpp
index db33f5f..63ae9e7 100644
--- a/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -2309,6 +2309,26 @@
SelectionDAG &DAG = DCI.DAG;
switch (N->getOpcode()) {
default: break;
+ case PPCISD::SHL:
+ if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(N->getOperand(0))) {
+ if (C->getValue() == 0) // 0 << V -> 0.
+ return N->getOperand(0);
+ }
+ break;
+ case PPCISD::SRL:
+ if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(N->getOperand(0))) {
+ if (C->getValue() == 0) // 0 >>u V -> 0.
+ return N->getOperand(0);
+ }
+ break;
+ case PPCISD::SRA:
+ if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(N->getOperand(0))) {
+ if (C->getValue() == 0 || // 0 >>s V -> 0.
+ C->isAllOnesValue()) // -1 >>s V -> -1.
+ return N->getOperand(0);
+ }
+ break;
+
case ISD::SINT_TO_FP:
if (TM.getSubtarget<PPCSubtarget>().has64BitSupport()) {
if (N->getOperand(0).getOpcode() == ISD::FP_TO_SINT) {