diff options
| author | Dan Gohman <gohman@apple.com> | 2008-05-23 18:05:39 +0000 |
|---|---|---|
| committer | Dan Gohman <gohman@apple.com> | 2008-05-23 18:05:39 +0000 |
| commit | a9e75631a79feeada17e21cb5ef1a0546a66dcaa (patch) | |
| tree | 738d9ee71dc31758b7b35a0c97e63cc6bdbda32e | |
| parent | 50f778deed6e615dd2080adf541557f7b72a0f00 (diff) | |
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
| -rw-r--r-- | lib/Target/X86/README-SSE.txt | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/lib/Target/X86/README-SSE.txt b/lib/Target/X86/README-SSE.txt index 7269fa2964..1f5f2037ce 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: |