[llvm-commits] [llvm] r122559 - /llvm/trunk/lib/Target/X86/README.txt

[Chris Lattner]

Author: lattner
Date: Sat Dec 25 21:53:31 2010
New Revision: 122559

URL: http://llvm.org/viewvc/llvm-project?rev=122559&view=rev
Log:
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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=122559&r1=122558&r2=122559&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/README.txt (original)
+++ llvm/trunk/lib/Target/X86/README.txt Sat Dec 25 21:53:31 2010
@@ -96,6 +96,97 @@
 
 //===---------------------------------------------------------------------===//
 
+This:
+
+void foo(void);
+void bar(int x, int *P) { 
+  x >>= 2;
+  if (x) 
+    foo();
+  *P = x;
+}
+
+compiles into:
+
+	movq	%rsi, %rbx
+	movl	%edi, %r14d
+	sarl	$2, %r14d
+	testl	%r14d, %r14d
+	je	LBB0_2
+
+Instead of doing an explicit test, we can use the flags off the sar.  This
+occurs in a bigger testcase like this, which is pretty common:
+
+#include <vector>
+
+
+int test1(std::vector<int> &X) {
+  int Sum = 0;
+  for (long i = 0, e = X.size(); i != e; ++i)
+    X[i] = 0;
+  return Sum;
+}
+compiles into:
+
+	movq	%rsi, %rbx
+	movl	%edi, %r14d
+	sarl	$2, %r14d
+	testl	%r14d, %r14d
+	je	LBB0_2
+
+Instead of doing an explicit test, we can use the flags off the sar.  This
+occurs in a bigger testcase like this, which is pretty common:
+
+#include <vector>
+
+
+int test1(std::vector<int> &X) {
+  int Sum = 0;
+  for (long i = 0, e = X.size(); i != e; ++i)
+    X[i] = 0;
+  return Sum;
+}
+compiles into:
+
+	movq	%rsi, %rbx
+	movl	%edi, %r14d
+	sarl	$2, %r14d
+	testl	%r14d, %r14d
+	je	LBB0_2
+
+Instead of doing an explicit test, we can use the flags off the sar.  This
+occurs in a bigger testcase like this, which is pretty common:
+
+#include <vector>
+
+
+int test1(std::vector<int> &X) {
+  int Sum = 0;
+  for (long i = 0, e = X.size(); i != e; ++i)
+    X[i] = 0;
+  return Sum;
+}
+compiles into:
+
+	movq	%rsi, %rbx
+	movl	%edi, %r14d
+	sarl	$2, %r14d
+	testl	%r14d, %r14d
+	je	LBB0_2
+
+Instead of doing an explicit test, we can use the flags off the sar.  This
+occurs in a bigger testcase like this, which is pretty common in bootstrap:
+
+#include <vector>
+int test1(std::vector<int> &X) {
+  int Sum = 0;
+  for (long i = 0, e = X.size(); i != e; ++i)
+    X[i] = 0;
+  return Sum;
+}
+
+//===---------------------------------------------------------------------===//
+
 Only use inc/neg/not instructions on processors where they are faster than
 add/sub/xor.  They are slower on the P4 due to only updating some processor
 flags.