Introduce a new technique for merging BasicBlock with Instruction sentinel by superpo...

[oota-llvm.git] / lib / Target / X86 / README-SSE.txt

diff --git a/lib/Target/X86/README-SSE.txt b/lib/Target/X86/README-SSE.txt
index 67cad42a3548a7281fb0978c8698bce5412460cd..71ad51c7984eb5ee07cd9563cb261ac35aff302d 100644 (file)
--- a/lib/Target/X86/README-SSE.txt
+++ b/lib/Target/X86/README-SSE.txt
@@ -840,42 +840,6 @@ _t:
        shufps  $132, %xmm2, %xmm0
        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