[llvm-commits] [llvm] r73471 - /llvm/trunk/lib/Target/X86/README.txt

[Chris Lattner]

Author: lattner
Date: Tue Jun 16 01:11:35 2009
New Revision: 73471

URL: http://llvm.org/viewvc/llvm-project?rev=73471&view=rev
Log:
I think instcombine should unconditionally do this xform.

Modified:
    llvm/trunk/lib/Target/X86/README.txt

Modified: llvm/trunk/lib/Target/X86/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/README.txt?rev=73471&r1=73470&r2=73471&view=diff

==============================================================================
--- llvm/trunk/lib/Target/X86/README.txt (original)
+++ llvm/trunk/lib/Target/X86/README.txt Tue Jun 16 01:11:35 2009
@@ -1858,8 +1858,23 @@
 	setne	%al
 	ret
 
-We could do this transformation in instcombine, but it's only clearly
-beneficial on platforms with a test instruction.
+This should definitely be done in instcombine, canonicalizing the range
+condition into a != condition.  We get this IR:
+
+define i32 @a(i32 %x) nounwind readnone {
+entry:
+	%0 = and i32 %x, 127		; <i32> [#uses=1]
+	%1 = icmp ugt i32 %0, 31		; <i1> [#uses=1]
+	%2 = zext i1 %1 to i32		; <i32> [#uses=1]
+	ret i32 %2
+}
+
+Instcombine prefers to strength reduce relational comparisons to equality
+comparisons when possible, this should be another case of that.  This could
+be handled pretty easily in InstCombiner::visitICmpInstWithInstAndIntCst, but it
+looks like InstCombiner::visitICmpInstWithInstAndIntCst should really already
+be redesigned to use ComputeMaskedBits and friends.
+
 
 //===---------------------------------------------------------------------===//
 Testcase: