//===---------------------------------------------------------------------===//
-Instcombine misses several of these cases (see the testcase in the patch):
-http://gcc.gnu.org/ml/gcc-patches/2006-10/msg01519.html
-
-//===---------------------------------------------------------------------===//
-
viterbi speeds up *significantly* if the various "history" related copy loops
are turned into memcpy calls at the source level. We need a "loops to memcpy"
pass.
exit value computation.
//===---------------------------------------------------------------------===//
+
+We miss a bunch of rotate opportunities on various targets, including ppc, x86,
+etc. On X86, we miss a bunch of 'rotate by variable' cases because the rotate
+matching code in dag combine doesn't look through truncates aggressively
+enough. Here are some testcases reduces from GCC PR17886:
+
+unsigned long long f(unsigned long long x, int y) {
+ return (x << y) | (x >> 64-y);
+}
+unsigned f2(unsigned x, int y){
+ return (x << y) | (x >> 32-y);
+}
+unsigned long long f3(unsigned long long x){
+ int y = 9;
+ return (x << y) | (x >> 64-y);
+}
+unsigned f4(unsigned x){
+ int y = 10;
+ return (x << y) | (x >> 32-y);
+}
+unsigned long long f5(unsigned long long x, unsigned long long y) {
+ return (x << 8) | ((y >> 48) & 0xffull);
+}
+unsigned long long f6(unsigned long long x, unsigned long long y, int z) {
+ switch(z) {
+ case 1:
+ return (x << 8) | ((y >> 48) & 0xffull);
+ case 2:
+ return (x << 16) | ((y >> 40) & 0xffffull);
+ case 3:
+ return (x << 24) | ((y >> 32) & 0xffffffull);
+ case 4:
+ return (x << 32) | ((y >> 24) & 0xffffffffull);
+ default:
+ return (x << 40) | ((y >> 16) & 0xffffffffffull);
+ }
+}
+
+On X86-64, we only handle f3/f4 right. On x86-32, several of these
+generate truly horrible code, instead of using shld and friends. On
+ARM, we end up with calls to L___lshrdi3/L___ashldi3 in f, which is
+badness. PPC64 misses f, f5 and f6. CellSPU aborts in isel.
+
+//===---------------------------------------------------------------------===//
+
+We do a number of simplifications in simplify libcalls to strength reduce
+standard library functions, but we don't currently merge them together. For
+example, it is useful to merge memcpy(a,b,strlen(b)) -> strcpy. This can only
+be done safely if "b" isn't modified between the strlen and memcpy of course.
+
+//===---------------------------------------------------------------------===//
+
+We should be able to evaluate this loop:
+
+int test(int x_offs) {
+ while (x_offs > 4)
+ x_offs -= 4;
+ return x_offs;
+}
+
+//===---------------------------------------------------------------------===//