Changes in directory llvm/lib/Target/X86:
README.txt updated: 1.162 -> 1.163
---
Log message:
new micro optzn
---
Diffs of the changes: (+30 -0)
README.txt | 30 ++++++++++++++++++++++++++++++
1 files changed, 30 insertions(+)
Index: llvm/lib/Target/X86/README.txt
diff -u llvm/lib/Target/X86/README.txt:1.162
llvm/lib/Target/X86/README.txt:1.163
--- llvm/lib/Target/X86/README.txt:1.162 Tue Apr 3 18:41:34 2007
+++ llvm/lib/Target/X86/README.txt Tue Apr 10 16:14:01 2007
@@ -1047,3 +1047,33 @@
}
+//===---------------------------------------------------------------------===//
+
+Consider:
+
+int isnegative(unsigned int X) {
+ return !(X < 2147483648U);
+}
+
+We current compile this to:
+
+define i32 @isnegative(i32 %X) {
+ icmp slt i32 %X, 0 ; <i1>:0 [#uses=1]
+ %retval = zext i1 %0 to i32 ; <i32> [#uses=1]
+ ret i32 %retval
+}
+
+and:
+
+_isnegative:
+ cmpl $0, 4(%esp)
+ sets %al
+ movzbl %al, %eax
+ ret
+
+We should produce:
+
+ movl 4(%esp), %eax
+ shrl $31, %eax
+ ret
+
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