From a9e75631a79feeada17e21cb5ef1a0546a66dcaa Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Fri, 23 May 2008 18:05:39 +0000 Subject: [PATCH] Elaborate on the entry on integer vector multiplication by constants. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51491 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/X86/README-SSE.txt | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/lib/Target/X86/README-SSE.txt b/lib/Target/X86/README-SSE.txt index 7269fa29645..1f5f2037cee 100644 --- a/lib/Target/X86/README-SSE.txt +++ b/lib/Target/X86/README-SSE.txt @@ -814,7 +814,7 @@ define <4 x i32> @f(<4 x i32> %i) nounwind { ret <4 x i32> %A } -Compiles into: +On targets without SSE4.1, this compiles into: LCPI1_0: ## <4 x i32> .long 10 @@ -846,6 +846,11 @@ _f: punpckldq %xmm2, %xmm0 ret +It would be better to synthesize integer vector multiplication by constants +using shifts and adds, pslld and paddd here. And even on targets with SSE4.1, +simple cases such as multiplication by powers of two would be better as +vector shifts than as multiplications. + //===---------------------------------------------------------------------===// We compile this: -- 2.34.1