[llvm-commits] [llvm] r47652 - /llvm/trunk/lib/Target/X86/README-X86-64.txt

[Chris Lattner]

Author: lattner
Date: Tue Feb 26 19:17:20 2008
New Revision: 47652

URL: http://llvm.org/viewvc/llvm-project?rev=47652&view=rev
Log:
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Modified:
    llvm/trunk/lib/Target/X86/README-X86-64.txt

Modified: llvm/trunk/lib/Target/X86/README-X86-64.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/README-X86-64.txt?rev=47652&r1=47651&r2=47652&view=diff

==============================================================================
--- llvm/trunk/lib/Target/X86/README-X86-64.txt (original)
+++ llvm/trunk/lib/Target/X86/README-X86-64.txt Tue Feb 26 19:17:20 2008
@@ -234,3 +234,30 @@
 allocation magic to make the hack go away (e.g. putting additional constraints
 on the result of the movb).
 
+//===---------------------------------------------------------------------===//
+
+This function:
+double a(double b) {return (unsigned)b;} 
+compiles to this code:
+
+_a:
+	subq	$8, %rsp
+	cvttsd2siq	%xmm0, %rax
+	movl	$4294967295, %ecx
+	andq	%rcx, %rax
+	cvtsi2sdq	%rax, %xmm0
+	addq	$8, %rsp
+	ret
+
+note the dead rsp adjustments.  Also, there is surely a better/shorter way 
+to clear the top 32-bits of a 64-bit register than movl+andq.  Testcase here:
+
+unsigned long long c(unsigned long long a) {return a&4294967295; }
+
+_c:
+	movl	$4294967295, %ecx
+	movq	%rdi, %rax
+	andq	%rcx, %rax
+	ret
+
+//===---------------------------------------------------------------------===//