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Author SHA1 Message Date
Benjamin Kramer b49b964b98 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.

llvm-svn: 127418
 2011-03-10 18:40:14 +00:00
Chris Lattner 1e8c032a6e 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

llvm-svn: 122186
 2010-12-19 20:03:11 +00:00
Chris Lattner 33dc3f0cfa 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.

llvm-svn: 122181
 2010-12-19 19:35:32 +00:00
Eli Friedman f99e7e6643 PR7853: fix a silly mistake introduced in r101899, and add a test to make sure 
it doesn't regress again.

llvm-svn: 110597
 2010-08-09 20:49:43 +00:00
Chris Lattner 249da5cb73 implement a simple instcombine xform that has been in the 
readme forever.

llvm-svn: 94318
 2010-01-23 18:49:30 +00:00
Chris Lattner 54f4e39956 optimize comparisons against cttz/ctlz/ctpop, patch by Alastair Lynn! 
llvm-svn: 92745
 2010-01-05 18:09:56 +00:00
Chris Lattner 9da1cb243b optimize cttz and ctlz when we can prove something about the 
leading/trailing bits.  Patch by Alastair Lynn!

llvm-svn: 92706
 2010-01-05 07:23:56 +00:00
Chris Lattner 8330daf733 add a few trivial instcombines for llvm.powi. 
llvm-svn: 92383
 2010-01-01 01:52:15 +00:00
Chris Lattner 1cc4cca193 add testcases for the foo_with_overflow op xforms added recently and 
fix bugs exposed by the tests.  Testcases from Alastair Lynn!

llvm-svn: 90056
 2009-11-29 02:57:29 +00:00
Chris Lattner 39c07b2eef if a 'with overflow' intrinsic just has the normal result used, simplify 
it to a normal binop.  Patch by Alastair Lynn, testcase by me.

llvm-svn: 86524
 2009-11-09 07:07:56 +00:00