If the false value for a select_cc is really simple (has no inputs), evaluate
it in the block. This codegens:
int %test(bool %c) {
%retval = select bool %c, int 17, int 1
ret int %retval
}
as:
_test:
rlwinm r2, r3, 0, 31, 31
li r2, 17
cmpwi cr0, r3, 0
bne .LBB_test_2 ;
.LBB_test_1: ;
li r2, 1
.LBB_test_2: ;
or r3, r2, r2
blr
instead of:
_test:
rlwinm r2, r3, 0, 31, 31
li r2, 17
li r4, 1
cmpwi cr0, r3, 0
bne .LBB_test_2 ;
.LBB_test_1: ;
or r2, r4, r4
.LBB_test_2: ;
or r3, r2, r2
blr
... which is one fewer instruction. The savings are more significant for
global address and constantfp nodes.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22946 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/PowerPC/PPCISelPattern.cpp b/lib/Target/PowerPC/PPCISelPattern.cpp
index caf6b39..4362a1d 100644
--- a/lib/Target/PowerPC/PPCISelPattern.cpp
+++ b/lib/Target/PowerPC/PPCISelPattern.cpp
@@ -1675,7 +1675,16 @@
// selecting it in the fallthrough basic block rather than here, which
// increases register pressure.
unsigned TrueValue = SelectExpr(N.getOperand(2));
- unsigned FalseValue = SelectExpr(N.getOperand(3));
+ unsigned FalseValue;
+
+ // If the false value is simple enough, evaluate it inline in the false
+ // block.
+ if (isa<ConstantSDNode>(N.getOperand(3)) ||
+ isa<ConstantFPSDNode>(N.getOperand(3)) ||
+ isa<GlobalAddressSDNode>(N.getOperand(3)))
+ FalseValue = 0;
+ else
+ FalseValue = SelectExpr(N.getOperand(3));
unsigned CCReg = SelectCC(N.getOperand(0), N.getOperand(1), CC);
Opc = getBCCForSetCC(CC);
@@ -1706,6 +1715,12 @@
// %FalseValue = ...
// # fallthrough to sinkMBB
BB = copy0MBB;
+
+ // If the false value is simple enough, evaluate it here, to avoid it being
+ // evaluated on the true edge.
+ if (FalseValue == 0)
+ FalseValue = SelectExpr(N.getOperand(3));
+
// Update machine-CFG edges
BB->addSuccessor(sinkMBB);