entered into RCS

From-SVN: r335

gcc/PROBLEMS

+3. When find_reloads is used to count number of spills needed
+it does not take into account the fact that a reload may
+turn out to be a dummy.
+
+I'm not sure this really happens any more.  Doesn't it find
+all the dummies on both passes?
+
+10.     movl a3@,a0
+	movl a3@(16),a1
+	clrb a0@(a1:l)
+is generated and may be worse than
+	movl a3@,a0
+	addl a3@(16),a0
+	clrb a0@
+If ordering of operands is improved, many more
+such cases will be generated from typical array accesses.
+
+38. Hack expand_mult so that if there is no same-modes multiply
+it will use a widening multiply and then truncate rather than
+calling the library.
+
+39. Hack expanding of division to notice cases for
+long -> short division.
+
+40. Represent divide insns as (DIV:SI ...) followed by
+a separate lowpart extract.  Represent remainder insns as DIV:SI
+followed by a separate highpart extract.  Then cse can work on
+the DIV:SI part.  Problem is, this may not be desirable on machines
+where computing the quotient alone does not necessarily give
+a remainder--such as the 68020 for long operands.
+
+52. Reloading can look at how reload_contents got set up.
+If it was copied from a register, just reload from that register.
+Otherwise, perhaps can change the previous insn to move the
+data via the reload reg, thus avoiding one memory ref.
+
+63. Potential problem in cc_status.value2, if it ever activates itself
+after a two-address subtraction (which currently cannot happen).
+It is supposed to compare the current value of the destination
+but eliminating it would use the results of the subtraction, equivalent
+to comparing the previous value of the destination.
+
+65. Should loops that neither start nor end with a break
+be rearranged to end with the last break?
+
+69. Define the floating point converting arithmetic instructions
+for the 68881.
+
+74. Combine loop opt with cse opt in one pass.  Do cse on each loop,
+then loop opt on that loop, and go from innermost loops outward.
+Make loop invariants available for cse at end of loop.
+
+85. pea can force a value to be reloaded into an areg
+which can make it worse than separate adding and pushing.
+This can only happen for adding something within addql range
+and it only loses if the qty becomes dead at that point
+so it can be added to with no copying.
+
+93. If a pseudo doesn't get a hard reg everywhere,
+can it get one during a loop?
+
+96. Can do SImode bitfield insns without reloading, but must
+alter the operands in special ways.
+
+99. final could check loop-entry branches to see if they
+screw up deletion of a test instruction.  If they do,
+can put another test instruction before the branch and
+make it conditional and redirect it.
+
+106. Aliasing may be impossible if data types of refs differ
+and data type of containing objects also differ.
+(But check this wrt unions.)
+
+108. Can speed up flow analysis by making a table saying which
+register is set and which registers are used by each instruction that
+only sets one register and only uses two.  This way avoid the tree
+walk for such instructions (most instructions).
+
+109. It is desirable to avoid converting INDEX to SImode if a
+narrower mode suffices, as HImode does on the 68000.
+How can this be done?
+
+110. Possible special combination pattern:
+If the two operands to a comparison die there and both come from insns
+that are identical except for replacing one operand with the other,
+throw away those insns.  Ok if insns being discarded are known 1 to 1.
+An andl #1 after a seq is 1 to 1, but how should compiler know that?
+
+112. Can convert float to unsigned int by subtracting a constant,
+converting to signed int, and changing the sign bit.
+
+117. Any number of slow zero-extensions in one loop, that have
+their clr insns moved out of the loop, can share one register
+if their original life spans are disjoint.
+But it may be hard to be sure of this since
+the life span data that regscan produces may be hard to interpret
+validly or may be incorrect after cse.
+
+118. In cse, when a bfext insn refers to a register, if the field
+corresponds to a halfword or a byte and the register is equivalent
+to a memory location, it would be possible to detect this and
+replace it with a simple memory reference.
+
+121. Insns that store two values cannot be moved out of loops.
+The code in scan_loop doesn't even try to deal with them.
+
+122. When insn-output.c turns a bit-test into a sign-test,
+it should see whether the cc is already set up with that sign.
+
+123. When a conditional expression is used as a function arg, it would
+be faster (and in some cases shorter) to push each alternative rather
+than compute in a register and push that.  This would require
+being able to specify "push this" as a target for expand_expr.
+
+124. On the 386, bad code results from foo (bar ()) when bar
+returns a double, because the pseudo used fails to get preferenced
+into an fp reg because of the distinction between regs 8 and 9.