diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Target/PowerPC/README.txt | 47 |
1 files changed, 26 insertions, 21 deletions
diff --git a/lib/Target/PowerPC/README.txt b/lib/Target/PowerPC/README.txt index 1286845..69c8150 100644 --- a/lib/Target/PowerPC/README.txt +++ b/lib/Target/PowerPC/README.txt @@ -52,7 +52,7 @@ This occurs in SPASS. as: xoris r0,r3,0x1234 - cmpwi cr0,r0,0x5678 + cmplwi cr0,r0,0x5678 beq cr0,L6 not: @@ -148,30 +148,35 @@ typedef struct program_t { 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 ===-------------------------------------------------------------------------=== |