Changes in directory llvm/lib/Target:
README.txt added (r1.1)
---
Log message:
target independent notes
---
Diffs of the changes: (+67 -0)
README.txt | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 67 insertions(+)
Index: llvm/lib/Target/README.txt
diff -c /dev/null llvm/lib/Target/README.txt:1.1
*** /dev/null Fri Feb 3 00:21:53 2006
--- llvm/lib/Target/README.txt Fri Feb 3 00:21:43 2006
***************
*** 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.
+
+
//===---------------------------------------------------------------------===//
+
+
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