Add some DAGCombines for (adde 0, 0, glue), which are useful to optimize legalized code for large integer arithmetic.

1. Inform users of ADDEs with two 0 operands that it never sets carry
2. Fold other ADDs or ADDCs into the ADDE if possible

It would be neat if we could do the same thing for SETCC+ADD eventually, but we can't do that in target independent code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126557 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/X86/adde-carry.ll

@@ -0,0 +1,26 @@
+; RUN: llc -march=x86-64 < %s | FileCheck %s -check-prefix=CHECK-64
+; RUN: llc -march=x86 < %s | FileCheck %s -check-prefix=CHECK-32
+
+define void @a(i64* nocapture %s, i64* nocapture %t, i64 %a, i64 %b, i64 %c) nounwind {
+entry:
+ %0 = zext i64 %a to i128
+ %1 = zext i64 %b to i128
+ %2 = add i128 %1, %0
+ %3 = zext i64 %c to i128
+ %4 = shl i128 %3, 64
+ %5 = add i128 %4, %2
+ %6 = lshr i128 %5, 64
+ %7 = trunc i128 %6 to i64
+ store i64 %7, i64* %s, align 8
+ %8 = trunc i128 %2 to i64
+ store i64 %8, i64* %t, align 8
+ ret void
+
+; CHECK-32: addl
+; CHECK-32: adcl
+; CHECK-32: adcl $0
+; CHECK-32: adcl $0
+
+; CHECK-64: addq
+; CHECK-64: adcq $0
+}