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| -rw-r--r-- | lib/Target/PowerPC/README.txt | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/lib/Target/PowerPC/README.txt b/lib/Target/PowerPC/README.txt index 8fad506f5c..898af148e0 100644 --- a/lib/Target/PowerPC/README.txt +++ b/lib/Target/PowerPC/README.txt @@ -466,3 +466,44 @@ we can convert to the "three address" instruction, to save code space. This only matters when we start generating cr logical ops. +===-------------------------------------------------------------------------=== + +We should compile these two functions to the same thing: + +#include <stdlib.h> +void f(int a, int b, int *P) { + *P = (a-b)>=0?(a-b):(b-a); +} +void g(int a, int b, int *P) { + *P = abs(a-b); +} + +Further, they should compile to something better than: + +_g: + subf r2, r4, r3 + subfic r3, r2, 0 + cmpwi cr0, r2, -1 + bgt cr0, LBB2_2 ; entry +LBB2_1: ; entry + mr r2, r3 +LBB2_2: ; entry + stw r2, 0(r5) + blr + +GCC produces: + +_g: + subf r4,r4,r3 + srawi r2,r4,31 + xor r0,r2,r4 + subf r0,r2,r0 + stw r0,0(r5) + blr + +... which is much nicer. + +This theoretically may help improve twolf slightly (used in dimbox.c:142?). + +===-------------------------------------------------------------------------=== + |