Commit Graph

9 Commits

Author SHA1 Message Date
Benjamin Kramer
1c10b8de46 BuildUDIV: If the divisor is even we can simplify the fixup of the multiplied value by introducing an early shift.
This allows us to compile "unsigned foo(unsigned x) { return x/28; }" into
	shrl	$2, %edi
	imulq	$613566757, %rdi, %rax
	shrq	$32, %rax
	ret

instead of
	movl    %edi, %eax
	imulq   $613566757, %rax, %rcx
	shrq    $32, %rcx
	subl    %ecx, %eax
	shrl    %eax
	addl    %ecx, %eax
	shrl    $4, %eax

on x86_64

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127829 91177308-0d34-0410-b5e6-96231b3b80d8
2011-03-17 20:39:14 +00:00
Cameron Zwarich
8d7285d0e5 The signed version of our "magic number" computation for the integer approximation
of a constant had a minor typo introduced when copying it from the book, which
caused it to favor negative approximations over positive approximations in many
cases. Positive approximations require fewer operations beyond the multiplication.

In the case of division by 3, we still generate code that is a single instruction
larger than GCC's code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126097 91177308-0d34-0410-b5e6-96231b3b80d8
2011-02-21 00:22:02 +00:00
Benjamin Kramer
9b108a338d Teach DAGCombine to fold fold (sra (trunc (sr x, c1)), c2) -> (trunc (sra x, c1+c2) when c1 equals the amount of bits that are truncated off.
This happens all the time when a smul is promoted to a larger type.

On x86-64 we now compile "int test(int x) { return x/10; }" into
  movslq  %edi, %rax
  imulq $1717986919, %rax, %rax
  movq  %rax, %rcx
  shrq  $63, %rcx
  sarq  $34, %rax <- used to be "shrq $32, %rax; sarl $2, %eax"
  addl  %ecx, %eax

This fires 96 times in gcc.c on x86-64.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124559 91177308-0d34-0410-b5e6-96231b3b80d8
2011-01-30 16:38:43 +00:00
Dale Johannesen
c72b18cdc8 Reapply 122353-122355 with fixes. 122354 was wrong;
the shift type was needed one place, the shift count
type another.  The transform in 123555 had the same
problem.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122366 91177308-0d34-0410-b5e6-96231b3b80d8
2010-12-21 21:55:50 +00:00
Dale Johannesen
d0cf2585a0 Revert 122353-122355 for the moment, they broke stuff.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122360 91177308-0d34-0410-b5e6-96231b3b80d8
2010-12-21 21:22:27 +00:00
Dale Johannesen
5ecc340e34 Get the type of a shift from the shift, not from its shift
count operand.  These should be the same but apparently are
not always, and this is cleaner anyway.  This improves the
code in an existing test.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122354 91177308-0d34-0410-b5e6-96231b3b80d8
2010-12-21 20:06:19 +00:00
Chris Lattner
33e77d3cb9 take care of some todos, transforming [us]mul_lohi into
a wider mul if the wider mul is legal.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121848 91177308-0d34-0410-b5e6-96231b3b80d8
2010-12-15 06:04:19 +00:00
Chris Lattner
2ff28e4b9e merge two tests
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121847 91177308-0d34-0410-b5e6-96231b3b80d8
2010-12-15 05:58:59 +00:00
Chris Lattner
bfc9749f0a rename test
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121697 91177308-0d34-0410-b5e6-96231b3b80d8
2010-12-13 08:39:40 +00:00