[ValueTracking] Add a framework for encoding implication rules

Summary:
This change adds a framework for adding more smarts to
`isImpliedCondition` around inequalities.  Informally,
`isImpliedCondition` will now try to prove "A < B ==> C < D" by proving
"C <= A && B <= D", since then it follows "C <= A < B <= D".

While this change is in principle NFC, I could not think of a way to not
handle cases like "i +_nsw 1 < L ==> i < L +_nsw 1" (that ValueTracking
did not handle before) while keeping the change understandable.  I've
added tests for these cases.

Reviewers: reames, majnemer, hfinkel

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D14368

llvm-svn: 252331

1 files changed, 24 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstSimplify/implies.ll b/llvm/test/Transforms/InstSimplify/implies.ll
index ac46b8d2828..8e5bbf2c897 100644
--- a/llvm/test/Transforms/InstSimplify/implies.ll
+++ b/llvm/test/Transforms/InstSimplify/implies.ll
@@ -92,6 +92,30 @@ define <4 x i1> @test6(<4 x i1> %a, <4 x i1> %b) {
   ret <4 x i1> %res
 }
 
+; i +_{nsw} 1 <s L  ==> i < L +_{nsw} 1
+define i1 @test7(i32 %length.i, i32 %i) {
+; CHECK-LABEL: @test7(
+; CHECK: ret i1 true
+  %iplus1 = add nsw i32 %i, 1
+  %len.plus.one = add nsw i32 %length.i, 1
+  %var29 = icmp slt i32 %i, %len.plus.one
+  %var30 = icmp slt i32 %iplus1, %length.i
+  %res = icmp ule i1 %var30, %var29
+  ret i1 %res
+}
+
+; i +_{nuw} 1 <s L  ==> i < L +_{nuw} 1
+define i1 @test8(i32 %length.i, i32 %i) {
+; CHECK-LABEL: @test8(
+; CHECK: ret i1 true
+  %iplus1 = add nuw i32 %i, 1
+  %len.plus.one = add nuw i32 %length.i, 1
+  %var29 = icmp ult i32 %i, %len.plus.one
+  %var30 = icmp ult i32 %iplus1, %length.i
+  %res = icmp ule i1 %var30, %var29
+  ret i1 %res
+}
+
 ; X >=(s) Y == X ==> Y (i1 1 becomes -1 for reasoning)
 define i1 @test_sge(i32 %length.i, i32 %i) {
 ; CHECK-LABEL: @test_sge