Re-apply [SCEV] Fix isLoopEntryGuardedByCond usage

ScalarEvolution::isKnownPredicate invokes isLoopEntryGuardedByCond without check
that SCEV is available at entry point of the loop. It is incorrect and fixed by patch.

To bugs additionally fixed:
assert is moved after the check whether loop is not a nullptr.
Usage of isLoopEntryGuardedByCond in ScalarEvolution::isImpliedCondOperandsViaNoOverflow
is guarded by isAvailableAtLoopEntry.

Reviewers: sanjoy, mkazantsev, anna, dorit, reames
Reviewed By: mkazantsev
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D42417

llvm-svn: 324204

1 files changed, 54 insertions, 0 deletions

diff --git a/llvm/test/Transforms/IndVarSimplify/inner-loop.ll b/llvm/test/Transforms/IndVarSimplify/inner-loop.ll
new file mode 100644
index 00000000000..b849c4e3423
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/inner-loop.ll
@@ -0,0 +1,54 @@
+; RUN: opt < %s -indvars -S | FileCheck %s
+
+; This is regression test for the bug in ScalarEvolution::isKnownPredicate.
+; It does not check whether SCEV is available at loop entry before invoking
+; and utility function isLoopEntryGuardedByCond and that leads to miscompile.
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128-ni:1"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @foo(i64)
+declare void @bar(i32)
+
+define void @test(i8* %arr) {
+entry:
+  br label %outer_header
+
+outer_header:
+  %i = phi i32 [40, %entry], [%i.next, %outer_latch]
+  %i.64 = sext i32 %i to i64
+  br label %inner_header
+
+inner_header:
+  %j = phi i32 [27, %outer_header], [%j.next, %inner_backedge]
+  %j1 = zext i32 %j to i64
+; The next 4 lines are required for avoid widening of %j and
+; SCEV at %cmp would not be AddRec.
+  %gep = getelementptr inbounds i8, i8*  %arr, i64 %j1
+  %ld = load i8, i8* %gep
+  %ec = icmp eq i8 %ld, 0
+  br i1 %ec, label %return, label %inner_backedge
+
+inner_backedge:
+  %cmp = icmp ult i32 %j, %i
+  %s = select i1 %cmp, i32 %i, i32 %j
+; Select should not be simplified because if
+; %i == 26 and %j == 27, %s should be equal to %j.
+; In case of a bug the instruction is simplified to
+; %s = select i1 true, i32 %0, i32 %j
+; CHECK-NOT: %s = select i1 true
+  call void @bar(i32 %s)
+  %j.next = add nsw i32 %j, -2
+  %cond = icmp ult i32 %j, 3
+  br i1 %cond, label %outer_latch, label %inner_header
+
+outer_latch:
+  %i.next = add i32 %i, -1
+  %cond2 = icmp sgt i32 %i.next, 13
+; This line is just for forcing widening of %i
+  call void @foo(i64 %i.64)
+  br i1 %cond2, label %outer_header, label %return
+
+return:
+  ret void
+}