[llvm-commits] [llvm] r41808 - in /llvm/trunk/lib/Target: ARM/README.txt PowerPC/README.txt X86/README.txt

[Chris Lattner]

Author: lattner
Date: Mon Sep 10 16:43:18 2007
New Revision: 41808

URL: http://llvm.org/viewvc/llvm-project?rev=41808&view=rev
Log:
Add some notes about better flag handling.

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

Modified: llvm/trunk/lib/Target/ARM/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/README.txt?rev=41808&r1=41807&r2=41808&view=diff

==============================================================================
--- llvm/trunk/lib/Target/ARM/README.txt (original)
+++ llvm/trunk/lib/Target/ARM/README.txt Mon Sep 10 16:43:18 2007
@@ -528,3 +528,48 @@
 This apparently occurs in real code.
 
 //===---------------------------------------------------------------------===//
+
+This:
+        #include <algorithm>
+        std::pair<unsigned, bool> full_add(unsigned a, unsigned b)
+        { return std::make_pair(a + b, a + b < a); }
+        bool no_overflow(unsigned a, unsigned b)
+        { return !full_add(a, b).second; }
+
+Should compile to:
+
+_Z8full_addjj:
+	adds	r2, r1, r2
+	movcc	r1, #0
+	movcs	r1, #1
+	str	r2, [r0, #0]
+	strb	r1, [r0, #4]
+	mov	pc, lr
+
+_Z11no_overflowjj:
+	cmn	r0, r1
+	movcs	r0, #0
+	movcc	r0, #1
+	mov	pc, lr
+
+not:
+
+__Z8full_addjj:
+        add r3, r2, r1
+        str r3, [r0]
+        mov r2, #1
+        mov r12, #0
+        cmp r3, r1
+        movlo r12, r2
+        str r12, [r0, #+4]
+        bx lr
+__Z11no_overflowjj:
+        add r3, r1, r0
+        mov r2, #1
+        mov r1, #0
+        cmp r3, r0
+        movhs r1, r2
+        mov r0, r1
+        bx lr
+
+//===---------------------------------------------------------------------===//

Modified: llvm/trunk/lib/Target/PowerPC/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/README.txt?rev=41808&r1=41807&r2=41808&view=diff

==============================================================================
--- llvm/trunk/lib/Target/PowerPC/README.txt (original)
+++ llvm/trunk/lib/Target/PowerPC/README.txt Mon Sep 10 16:43:18 2007
@@ -677,5 +677,33 @@
         cmplwi cr0, r6, 33920
         bne cr0, LBB1_1
 
-===-------------------------------------------------------------------------===
+//===---------------------------------------------------------------------===//
+
+This:
+        #include <algorithm>
+        inline std::pair<unsigned, bool> full_add(unsigned a, unsigned b)
+        { return std::make_pair(a + b, a + b < a); }
+        bool no_overflow(unsigned a, unsigned b)
+        { return !full_add(a, b).second; }
+
+Should compile to:
+
+__Z11no_overflowjj:
+        add r4,r3,r4
+        subfc r3,r3,r4
+        li r3,0
+        adde r3,r3,r3
+        blr
+
+(or better) not:
+
+__Z11no_overflowjj:
+        add r2, r4, r3
+        cmplw cr7, r2, r3
+        mfcr r2
+        rlwinm r2, r2, 29, 31, 31
+        xori r3, r2, 1
+        blr 
+
+//===---------------------------------------------------------------------===//
 

Modified: llvm/trunk/lib/Target/X86/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/README.txt?rev=41808&r1=41807&r2=41808&view=diff

==============================================================================
--- llvm/trunk/lib/Target/X86/README.txt (original)
+++ llvm/trunk/lib/Target/X86/README.txt Mon Sep 10 16:43:18 2007
@@ -1178,3 +1178,30 @@
 be pretty easy, and will nuke all the copies.
 
 //===---------------------------------------------------------------------===//
+
+This:
+        #include <algorithm>
+        inline std::pair<unsigned, bool> full_add(unsigned a, unsigned b)
+        { return std::make_pair(a + b, a + b < a); }
+        bool no_overflow(unsigned a, unsigned b)
+        { return !full_add(a, b).second; }
+
+Should compile to:
+
+
+        _Z11no_overflowjj:
+                addl    %edi, %esi
+                setae   %al
+                ret
+
+on x86-64, not:
+
+__Z11no_overflowjj:
+        addl    %edi, %esi
+        cmpl    %edi, %esi
+        setae   %al
+        movzbl  %al, %eax
+        ret
+
+
+//===---------------------------------------------------------------------===//