diff --git a/llvm/lib/Target/README.txt b/llvm/lib/Target/README.txt new file mode 100644 index 000000000000..2a0d8e121cac --- /dev/null +++ b/llvm/lib/Target/README.txt @@ -0,0 +1,67 @@ +Target Independent Opportunities: + +===-------------------------------------------------------------------------=== + +FreeBench/mason contains code like this: + +static p_type m0u(p_type p) { + int m[]={0, 8, 1, 2, 16, 5, 13, 7, 14, 9, 3, 4, 11, 12, 15, 10, 17, 6}; + p_type pu; + pu.a = m[p.a]; + pu.b = m[p.b]; + pu.c = m[p.c]; + return pu; +} + +We currently compile this into a memcpy from a static array into 'm', then +a bunch of loads from m. It would be better to avoid the memcpy and just do +loads from the static array. + +===-------------------------------------------------------------------------=== + +Get the C front-end to expand hypot(x,y) -> llvm.sqrt(x*x+y*y) when errno and +precision don't matter (ffastmath). Misc/mandel will like this. :) + +===-------------------------------------------------------------------------=== + +For all targets, not just X86: +When llvm.memcpy, llvm.memset, or llvm.memmove are lowered, they should be +optimized to a few store instructions if the source is constant and the length +is smallish (< 8). This will greatly help some tests like Shootout/strcat.c +and fldry. + +//===---------------------------------------------------------------------===// + +Solve this DAG isel folding deficiency: + +int X, Y; + +void fn1(void) +{ + X = X | (Y << 3); +} + +compiles to + +fn1: + movl Y, %eax + shll $3, %eax + orl X, %eax + movl %eax, X + ret + +The problem is the store's chain operand is not the load X but rather +a TokenFactor of the load X and load Y, which prevents the folding. + +There are two ways to fix this: + +1. The dag combiner can start using alias analysis to realize that y/x + don't alias, making the store to X not dependent on the load from Y. +2. The generated isel could be made smarter in the case it can't + disambiguate the pointers. + +Number 1 is the preferred solution. + +//===---------------------------------------------------------------------===// + +