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| -rw-r--r-- | lib/Target/PowerPC/README.txt | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/lib/Target/PowerPC/README.txt b/lib/Target/PowerPC/README.txt index 463e406779..8858296699 100644 --- a/lib/Target/PowerPC/README.txt +++ b/lib/Target/PowerPC/README.txt @@ -217,3 +217,26 @@ _test: stw r2, 0(r3) blr +===-------------------------------------------------------------------------=== + +Compile this: + +int %f1(int %a, int %b) { + %tmp.1 = and int %a, 15 ; <int> [#uses=1] + %tmp.3 = and int %b, 240 ; <int> [#uses=1] + %tmp.4 = or int %tmp.3, %tmp.1 ; <int> [#uses=1] + ret int %tmp.4 +} + +without a copy. We make this currently: + +_f1: + rlwinm r2, r4, 0, 24, 27 + rlwimi r2, r3, 0, 28, 31 + or r3, r2, r2 + blr + +The two-addr pass or RA needs to learn when it is profitable to commute an +instruction to avoid a copy AFTER the 2-addr instruction. The 2-addr pass +currently only commutes to avoid inserting a copy BEFORE the two addr instr. + |