[GVN LoadPRE] Add test to show an opportunty.

We can use context to prove that load can be safely executed
at a point where load is being hoisted.

llvm/test/Transforms/GVN/loadpre-context.ll

@@ -0,0 +1,144 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -gvn --basic-aa -S | FileCheck %s
+
+; load may be speculated, adress is not null using context search.
+; There is a critical edge.
+define i32 @loadpre_critical_edge(i32* align 8 dereferenceable_or_null(48) %arg, i32 %N) {
+; CHECK-LABEL: @loadpre_critical_edge(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32* [[ARG:%.*]], null
+; CHECK-NEXT:    br i1 [[CMP]], label [[NULL_EXIT:%.*]], label [[HEADER:%.*]]
+; CHECK:       header:
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[HEADER]] ]
+; CHECK-NEXT:    [[NEW_V:%.*]] = call i32 @foo(i32 [[IV]])
+; CHECK-NEXT:    [[V:%.*]] = load i32, i32* [[ARG]], align 4
+; CHECK-NEXT:    [[SUM:%.*]] = add i32 [[NEW_V]], [[V]]
+; CHECK-NEXT:    store i32 [[SUM]], i32* [[ARG]], align 4
+; CHECK-NEXT:    [[IV_NEXT]] = add i32 [[IV]], 1
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i32 [[IV_NEXT]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[COND]], label [[EXIT:%.*]], label [[HEADER]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 [[SUM]]
+; CHECK:       null_exit:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %cmp = icmp eq i32* %arg, null
+  br i1 %cmp, label %null_exit, label %header
+
+header:
+  %iv = phi i32 [0, %entry], [%iv.next, %header]
+  %new_v = call i32 @foo(i32 %iv)
+  %v = load i32, i32* %arg
+  %sum = add i32 %new_v, %v
+  store i32 %sum, i32* %arg
+  %iv.next = add i32 %iv, 1
+  %cond = icmp eq i32 %iv.next, %N
+  br i1 %cond, label %exit, label %header
+
+exit:
+  ret i32 %sum
+
+null_exit:
+  ret i32 0
+}
+
+; load may be speculated, adress is not null using context search.
+define i32 @loadpre_basic(i32* align 8 dereferenceable_or_null(48) %arg, i32 %N) {
+; CHECK-LABEL: @loadpre_basic(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32* [[ARG:%.*]], null
+; CHECK-NEXT:    br i1 [[CMP]], label [[NULL_EXIT:%.*]], label [[PREHEADER:%.*]]
+; CHECK:       preheader:
+; CHECK-NEXT:    br label [[HEADER:%.*]]
+; CHECK:       header:
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[PREHEADER]] ], [ [[IV_NEXT:%.*]], [[HEADER]] ]
+; CHECK-NEXT:    [[NEW_V:%.*]] = call i32 @foo(i32 [[IV]])
+; CHECK-NEXT:    [[V:%.*]] = load i32, i32* [[ARG]], align 4
+; CHECK-NEXT:    [[SUM:%.*]] = add i32 [[NEW_V]], [[V]]
+; CHECK-NEXT:    store i32 [[SUM]], i32* [[ARG]], align 4
+; CHECK-NEXT:    [[IV_NEXT]] = add i32 [[IV]], 1
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i32 [[IV_NEXT]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[COND]], label [[EXIT:%.*]], label [[HEADER]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 [[SUM]]
+; CHECK:       null_exit:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %cmp = icmp eq i32* %arg, null
+  br i1 %cmp, label %null_exit, label %preheader
+
+preheader:
+  br label %header
+
+header:
+  %iv = phi i32 [0, %preheader], [%iv.next, %header]
+  %new_v = call i32 @foo(i32 %iv)
+  %v = load i32, i32* %arg
+  %sum = add i32 %new_v, %v
+  store i32 %sum, i32* %arg
+  %iv.next = add i32 %iv, 1
+  %cond = icmp eq i32 %iv.next, %N
+  br i1 %cond, label %exit, label %header
+
+exit:
+  ret i32 %sum
+
+null_exit:
+  ret i32 0
+}
+
+; load cannot be speculated, adress is not null check does not dominate the loop.
+define i32 @loadpre_maybe_null(i32* align 8 dereferenceable_or_null(48) %arg, i32 %N, i1 %c) {
+; CHECK-LABEL: @loadpre_maybe_null(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[C:%.*]], label [[NULL_CHECK:%.*]], label [[PREHEADER:%.*]]
+; CHECK:       null_check:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32* [[ARG:%.*]], null
+; CHECK-NEXT:    br i1 [[CMP]], label [[NULL_EXIT:%.*]], label [[PREHEADER]]
+; CHECK:       preheader:
+; CHECK-NEXT:    br label [[HEADER:%.*]]
+; CHECK:       header:
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[PREHEADER]] ], [ [[IV_NEXT:%.*]], [[HEADER]] ]
+; CHECK-NEXT:    [[NEW_V:%.*]] = call i32 @foo(i32 [[IV]])
+; CHECK-NEXT:    [[V:%.*]] = load i32, i32* [[ARG]], align 4
+; CHECK-NEXT:    [[SUM:%.*]] = add i32 [[NEW_V]], [[V]]
+; CHECK-NEXT:    store i32 [[SUM]], i32* [[ARG]], align 4
+; CHECK-NEXT:    [[IV_NEXT]] = add i32 [[IV]], 1
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i32 [[IV_NEXT]], [[N:%.*]]
+; CHECK-NEXT:    br i1 [[COND]], label [[EXIT:%.*]], label [[HEADER]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i32 [[SUM]]
+; CHECK:       null_exit:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  br i1 %c, label %null_check, label %preheader
+
+null_check:
+  %cmp = icmp eq i32* %arg, null
+  br i1 %cmp, label %null_exit, label %preheader
+
+preheader:
+  br label %header
+
+header:
+  %iv = phi i32 [0, %preheader], [%iv.next, %header]
+  %new_v = call i32 @foo(i32 %iv)
+  %v = load i32, i32* %arg
+  %sum = add i32 %new_v, %v
+  store i32 %sum, i32* %arg
+  %iv.next = add i32 %iv, 1
+  %cond = icmp eq i32 %iv.next, %N
+  br i1 %cond, label %exit, label %header
+
+exit:
+  ret i32 %sum
+
+null_exit:
+  ret i32 0
+}
+
+; Does not guarantee that returns.
+declare i32 @foo(i32) readnone