Add support to indvars for optimizing sadd.with.overflow.

Split sadd.with.overflow into add + sadd.with.overflow to allow
analysis and optimization. This should ideally be done after
InstCombine, which can perform code motion (eventually indvars should
run after all canonical instcombines). We want ISEL to recombine the
add and the check, at least on x86.

This is currently under an option for reducing live induction
variables: -liv-reduce. The next step is reducing liveness of IVs that
are live out of the overflow check paths. Once the related
optimizations are fully developed, reviewed and tested, I do expect
this to become default.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197926 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/IndVarSimplify/overflowcheck.ll

@@ -0,0 +1,56 @@
+; RUN: opt < %s -indvars -liv-reduce -S | FileCheck %s
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx"
+
+; CHECK-LABEL: @addwithoverflow
+; CHECK-LABEL: loop1:
+; CHECK-NOT: zext
+; CHECK: add nsw
+; CHECK: @llvm.sadd.with.overflow
+; CHECK-LABEL: loop2:
+; CHECK-NOT: extractvalue
+; CHECK: add nuw nsw
+; CHECK: @llvm.sadd.with.overflow
+; CHECK-LABEL: loop3:
+; CHECK-NOT: extractvalue
+; CHECK: ret
+define i64 @addwithoverflow(i32 %n, i64* %a) {
+entry:
+  br label %loop0
+
+loop0:
+  %i = phi i32 [ 0, %entry ], [ %i1val, %loop3 ]
+  %s = phi i32 [ 0, %entry ], [ %addsval, %loop3 ]
+  %bc = icmp ult i32 %i, %n
+  br i1 %bc, label %loop1, label %exit
+
+loop1:
+  %zxt = zext i32 %i to i64
+  %ofs = shl nuw nsw i64 %zxt, 3
+  %gep = getelementptr i64* %a, i64 %zxt
+  %v = load i64* %gep, align 8
+  %truncv = trunc i64 %v to i32
+  %adds = call { i32, i1 } @llvm.sadd.with.overflow.i32(i32 %s, i32 %truncv)
+  %ovflows = extractvalue { i32, i1 } %adds, 1
+  br i1 %ovflows, label %exit, label %loop2
+
+loop2:
+  %addsval = extractvalue { i32, i1 } %adds, 0
+  %i1 = call { i32, i1 } @llvm.sadd.with.overflow.i32(i32 %i, i32 1)
+  %i1check = extractvalue { i32, i1 } %i1, 1
+  br i1 %i1check, label %exit, label %loop3
+
+loop3:
+  %i1val = extractvalue { i32, i1 } %i1, 0
+  %test = icmp slt i32 %i1val, %n
+  br i1 %test, label %return, label %loop0
+
+return:
+  %ret = zext i32 %addsval to i64
+  ret i64 %ret
+
+exit:
+  unreachable
+}
+
+declare { i32, i1 } @llvm.sadd.with.overflow.i32(i32, i32)