Changes in directory llvm/lib/Target/X86:
README.txt updated: 1.151 -> 1.152
---
Log message:
add some notes
---
Diffs of the changes: (+68 -0)
README.txt | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 68 insertions(+)
Index: llvm/lib/Target/X86/README.txt
diff -u llvm/lib/Target/X86/README.txt:1.151
llvm/lib/Target/X86/README.txt:1.152
--- llvm/lib/Target/X86/README.txt:1.151 Fri Jan 12 13:20:47 2007
+++ llvm/lib/Target/X86/README.txt Mon Jan 15 00:25:39 2007
@@ -762,3 +762,71 @@
We should inline lrintf and probably other libc functions.
//===---------------------------------------------------------------------===//
+
+Start using the flags more. For example, compile:
+
+int add_zf(int *x, int y, int a, int b) {
+ if ((*x += y) == 0)
+ return a;
+ else
+ return b;
+}
+
+to:
+ addl %esi, (%rdi)
+ movl %edx, %eax
+ cmovne %ecx, %eax
+ ret
+instead of:
+
+_add_zf:
+ addl (%rdi), %esi
+ movl %esi, (%rdi)
+ testl %esi, %esi
+ cmove %edx, %ecx
+ movl %ecx, %eax
+ ret
+
+and:
+
+int add_zf(int *x, int y, int a, int b) {
+ if ((*x + y) < 0)
+ return a;
+ else
+ return b;
+}
+
+to:
+
+add_zf:
+ addl (%rdi), %esi
+ movl %edx, %eax
+ cmovns %ecx, %eax
+ ret
+
+instead of:
+
+_add_zf:
+ addl (%rdi), %esi
+ testl %esi, %esi
+ cmovs %edx, %ecx
+ movl %ecx, %eax
+ ret
+
+//===---------------------------------------------------------------------===//
+
+This:
+#include <math.h>
+int foo(double X) { return isnan(X); }
+
+compiles to (-m64):
+
+_foo:
+ pxor %xmm1, %xmm1
+ ucomisd %xmm1, %xmm0
+ setp %al
+ movzbl %al, %eax
+ ret
+
+the pxor is not needed, we could compare the value against itself.
+
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