Changes in directory llvm/lib/Target/PowerPC:
README.txt updated: 1.63 -> 1.64
---
Log message:
readme updates
---
Diffs of the changes: (+26 -21)
README.txt | 47 ++++++++++++++++++++++++++---------------------
1 files changed, 26 insertions(+), 21 deletions(-)
Index: llvm/lib/Target/PowerPC/README.txt
diff -u llvm/lib/Target/PowerPC/README.txt:1.63
llvm/lib/Target/PowerPC/README.txt:1.64
--- llvm/lib/Target/PowerPC/README.txt:1.63 Wed Feb 8 00:43:51 2006
+++ llvm/lib/Target/PowerPC/README.txt Mon Feb 27 16:08:36 2006
@@ -52,7 +52,7 @@
as:
xoris r0,r3,0x1234
- cmpwi cr0,r0,0x5678
+ cmplwi cr0,r0,0x5678
beq cr0,L6
not:
@@ -148,30 +148,35 @@
void AdjustBitfields(program* prog, unsigned int fmt1)
{
- unsigned int shift = 0;
- unsigned int texCount = 0;
- unsigned int i;
-
- for (i = 0; i < 8; i++)
- {
- prog->array[i].bitfields.field0 = texCount;
- prog->array[i].bitfields.field1 = texCount + 1;
- prog->array[i].bitfields.field2 = texCount + 2;
- prog->array[i].bitfields.field3 = texCount + 3;
-
- texCount += (fmt1 >> shift) & 0x7;
- shift += 3;
- }
+ prog->array[0].bitfields.field0 = fmt1;
+ prog->array[0].bitfields.field1 = fmt1 + 1;
}
-In the loop above, the bitfield adds get generated as
-(add (shl bitfield, C1), (shl C2, C1)) where C2 is 1, 2 or 3.
+We currently generate:
-Since the input to the (or and, and) is an (add) rather than a (shl), the shift
-doesn't get folded into the rlwimi instruction. We should ideally see through
-things like this, rather than forcing llvm to generate the equivalent
+_AdjustBitfields:
+ lwz r2, 0(r3)
+ addi r5, r4, 1
+ rlwinm r2, r2, 0, 0, 19
+ rlwinm r5, r5, 6, 20, 25
+ rlwimi r2, r4, 0, 26, 31
+ or r2, r2, r5
+ stw r2, 0(r3)
+ blr
+
+We should teach someone that or (rlwimi, rlwinm) with disjoint masks can be
+turned into rlwimi (rlwimi)
-(shl (add bitfield, C2), C1) with some kind of mask.
+The better codegen would be:
+
+_AdjustBitfields:
+ lwz r0,0(r3)
+ rlwinm r4,r4,0,0xff
+ rlwimi r0,r4,0,26,31
+ addi r4,r4,1
+ rlwimi r0,r4,6,20,25
+ stw r0,0(r3)
+ blr
===-------------------------------------------------------------------------===
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