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Diffstat (limited to 'lib/Target/X86/README-SSE.txt')
| -rw-r--r-- | lib/Target/X86/README-SSE.txt | 31 |
1 files changed, 0 insertions, 31 deletions
diff --git a/lib/Target/X86/README-SSE.txt b/lib/Target/X86/README-SSE.txt index 496b704ee8..adfa7fa123 100644 --- a/lib/Target/X86/README-SSE.txt +++ b/lib/Target/X86/README-SSE.txt @@ -517,37 +517,6 @@ to <2 x i64> ops being so bad. //===---------------------------------------------------------------------===// -'select' on vectors and scalars could be a whole lot better. We currently -lower them to conditional branches. On x86-64 for example, we compile this: - -double test(double a, double b, double c, double d) { return a<b ? c : d; } - -to: - -_test: - ucomisd %xmm0, %xmm1 - ja LBB1_2 # entry -LBB1_1: # entry - movapd %xmm3, %xmm2 -LBB1_2: # entry - movapd %xmm2, %xmm0 - ret - -instead of: - -_test: - cmpltsd %xmm1, %xmm0 - andpd %xmm0, %xmm2 - andnpd %xmm3, %xmm0 - orpd %xmm2, %xmm0 - ret - -For unpredictable branches, the later is much more efficient. This should -just be a matter of having scalar sse map to SELECT_CC and custom expanding -or iseling it. - -//===---------------------------------------------------------------------===// - LLVM currently generates stack realignment code, when it is not necessary needed. The problem is that we need to know about stack alignment too early, before RA runs. |