Changes in directory llvm/lib/Target:
README.txt updated: 1.37 -> 1.38
---
Log message:
add a note noticed through source inspection
---
Diffs of the changes: (+30 -3)
README.txt | 33 ++++++++++++++++++++++++++++++---
1 files changed, 30 insertions(+), 3 deletions(-)
Index: llvm/lib/Target/README.txt
diff -u llvm/lib/Target/README.txt:1.37 llvm/lib/Target/README.txt:1.38
--- llvm/lib/Target/README.txt:1.37 Fri Sep 15 15:31:36 2006
+++ llvm/lib/Target/README.txt Sat Sep 16 18:57:51 2006
@@ -198,11 +198,11 @@
%struct.Y = type { %struct.X }
ulong %bar() {
%retval = alloca %struct.Y, align 8 ; <%struct.Y*>
[#uses=3]
- %tmp12 = getelementptr %struct.Y* %retval, int 0, uint 0, uint 0
; <int*> [#uses=1]
+ %tmp12 = getelementptr %struct.Y* %retval, int 0, uint 0, uint 0
store int 0, int* %tmp12
- %tmp15 = getelementptr %struct.Y* %retval, int 0, uint 0, uint 1
; <int*> [#uses=1]
+ %tmp15 = getelementptr %struct.Y* %retval, int 0, uint 0, uint 1
store int 1, int* %tmp15
- %retval = cast %struct.Y* %retval to ulong* ; <ulong*>
[#uses=1]
+ %retval = cast %struct.Y* %retval to ulong*
%retval = load ulong* %retval ; <ulong> [#uses=1]
ret ulong %retval
}
@@ -247,3 +247,30 @@
on targets that have popcnt but not ctlz. itanium, what else?
+//===---------------------------------------------------------------------===//
+
+quantum_sigma_x in 462.libquantum contains the following loop:
+
+ for(i=0; i<reg->size; i++)
+ {
+ /* Flip the target bit of each basis state */
+ reg->node[i].state ^= ((MAX_UNSIGNED) 1 << target);
+ }
+
+Where MAX_UNSIGNED/state is a 64-bit int. On a 32-bit platform it would be
just
+so cool to turn it into something like:
+
+ if (target < 32) {
+ for(i=0; i<reg->size; i++)
+ reg->node[i].state ^= ((int) (1 << target));
+ } else {
+ for(i=0; i<reg->size; i++)
+ reg->node[i].state ^= (long long)((int) (1 << (target-32))) << 32;
+ }
+
+... which would only do one 32-bit XOR per loop iteration instead of two.
+
+It would also be nice to recognize the reg->size doesn't alias reg->node[i],
but
+alas...
+
+//===---------------------------------------------------------------------===//
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