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10 Commits

Author SHA1 Message Date
Benjamin Kramer
6b96fe7e14 InstCombine: Turn umul_with_overflow into mul nuw if we can prove that it cannot overflow. 
This happens a lot in clang-compiled C++ code because it adds overflow checks to operator new[]:
  unsigned *foo(unsigned n) { return new unsigned[n]; }
We can optimize away the overflow check on 64 bit targets because (uint64_t)n*4 cannot overflow.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127418 91177308-0d34-0410-b5e6-96231b3b80d8
 2011-03-10 18:40:14 +00:00
Chris Lattner
a34b3cf953 X86 supports i8/i16 overflow ops (except i8 multiplies), we should 
generate them.  

Now we compile:

define zeroext i8 @X(i8 signext %a, i8 signext %b) nounwind ssp {
entry:
  %0 = tail call %0 @llvm.sadd.with.overflow.i8(i8 %a, i8 %b)
  %cmp = extractvalue %0 %0, 1
  br i1 %cmp, label %if.then, label %if.end

into:

_X:                                     ## @X
## BB#0:                                ## %entry
	subl	$12, %esp
	movb	16(%esp), %al
	addb	20(%esp), %al
	jo	LBB0_2

Before we were generating:

_X:                                     ## @X
## BB#0:                                ## %entry
	pushl	%ebp
	movl	%esp, %ebp
	subl	$8, %esp
	movb	12(%ebp), %al
	testb	%al, %al
	setge	%cl
	movb	8(%ebp), %dl
	testb	%dl, %dl
	setge	%ah
	cmpb	%cl, %ah
	sete	%cl
	addb	%al, %dl
	testb	%dl, %dl
	setge	%al
	cmpb	%al, %ah
	setne	%al
	andb	%cl, %al
	testb	%al, %al
	jne	LBB0_2




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122186 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-12-19 20:03:11 +00:00
Chris Lattner
26b482d7a7 optimize uadd(x, cst) into a comparison when the normal 
result is dead.  This is required for my next patch to not
regress the testsuite.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122181 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-12-19 19:35:32 +00:00
Eli Friedman
4fffb345ed PR7853: fix a silly mistake introduced in r101899, and add a test to make sure 
it doesn't regress again.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110597 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-08-09 20:49:43 +00:00
Chris Lattner
818ff34bc0 implement a simple instcombine xform that has been in the 
readme forever.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94318 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-01-23 18:49:30 +00:00
Chris Lattner
033574074d optimize comparisons against cttz/ctlz/ctpop, patch by Alastair Lynn! 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92745 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-01-05 18:09:56 +00:00
Chris Lattner
16507fe9fd optimize cttz and ctlz when we can prove something about the 
leading/trailing bits.  Patch by Alastair Lynn!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92706 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-01-05 07:23:56 +00:00
Chris Lattner
d27f911b23 add a few trivial instcombines for llvm.powi. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92383 91177308-0d34-0410-b5e6-96231b3b80d8
 2010-01-01 01:52:15 +00:00
Chris Lattner
cd188e9665 add testcases for the foo_with_overflow op xforms added recently and 
fix bugs exposed by the tests.  Testcases from Alastair Lynn!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90056 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-11-29 02:57:29 +00:00
Chris Lattner
7e606e2e98 if a 'with overflow' intrinsic just has the normal result used, simplify 
it to a normal binop.  Patch by Alastair Lynn, testcase by me.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86524 91177308-0d34-0410-b5e6-96231b3b80d8
 2009-11-09 07:07:56 +00:00