[llvm-commits] [llvm] r63752 - /llvm/trunk/lib/Target/X86/README-SSE.txt

[Chris Lattner]

Author: lattner
Date: Wed Feb  4 13:09:07 2009
New Revision: 63752

URL: http://llvm.org/viewvc/llvm-project?rev=63752&view=rev
Log:
Bill implemented this.

Modified:
    llvm/trunk/lib/Target/X86/README-SSE.txt

Modified: llvm/trunk/lib/Target/X86/README-SSE.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/README-SSE.txt?rev=63752&r1=63751&r2=63752&view=diff

==============================================================================
--- llvm/trunk/lib/Target/X86/README-SSE.txt (original)
+++ llvm/trunk/lib/Target/X86/README-SSE.txt Wed Feb  4 13:09:07 2009
@@ -841,42 +841,6 @@
 	movaps	%xmm0, 0
 
 //===---------------------------------------------------------------------===//
-rdar://6037315
-
-llvm-gcc-4.2 does the following for uint32_t -> float conversions on i386:
-
-	uint32_t x;
-	float y = (float)x;
-
-becomes:
-
-movl	%eax,		-8(%ebp)	// write x to the stack
-movl	$0x3ff00000,	-4(%ebp)	// 2^52 + x as a double at -4(%ebp)
-movsd	-8(%ebp),		%xmm0
-subsd	[2^52 double], 	%xmm0	// subtract 2^52 -- this is exact
-cvtsd2ss %xmm0,		%xmm0	// convert to single -- rounding happens here
-
-On merom/yonah, this takes a substantial stall.  The following is a much 
-better option:
-
-movd	%eax,		%xmm0	// load x into low word of xmm0
-movsd	[2^52 double],	%xmm1 	// load 2^52 into xmm1
-orpd	%xmm1,		%xmm0	// 2^52 + x in double precision
-subsd	%xmm1,		%xmm0	// x in double precision
-cvtsd2ss %xmm0,		%xmm0	// x rounded to single precision
-
-IF we don't already need PIC, then the following is even faster still, at a 
-small cost to code size:
-
-movl		$0x3ff00000,	%ecx		// conjure high word of 2^52
-movd		%ecx,		%xmm1
-movss	%eax,		%xmm0	// load x into low word of xmm0
-psllq		$32,			%xmm1	// 2^52
-orpd		%xmm1,		%xmm0	// 2^52 + x in double precision
-subsd		%xmm1,		%xmm0	// x in double precision
-cvtsd2ss	%xmm0,		%xmm0	// x in single precision
-
-//===---------------------------------------------------------------------===//
 rdar://5907648
 
 This function: