[ValueTracking] Fix the identity case (LHS => RHS) when the LHS is false.

Prior to this commit both of the added test cases were passing.  However, in the
latter case (test7) we were doing a lot more work to arrive at the same answer
(i.e., we were using isImpliedCondMatchingOperands() to determine the
implication.).

llvm-svn: 307400

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 514b8f2..5285fa5 100644 (file)
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4405,8 +4405,8 @@ Optional<bool> llvm::isImpliedCondition(const Value *LHS, const Value *RHS,
   assert(OpTy->getScalarType()->isIntegerTy(1));
 
   // LHS ==> RHS by definition
-  if (!LHSIsFalse && LHS == RHS)
-    return true;
+  if (LHS == RHS)
+    return !LHSIsFalse;
 
   if (OpTy->isVectorTy())
     // TODO: extending the code below to handle vectors

diff --git a/llvm/test/Transforms/InstCombine/select-implied.ll b/llvm/test/Transforms/InstCombine/select-implied.ll
index 6b2ec7f..2558745 100644 (file)
--- a/llvm/test/Transforms/InstCombine/select-implied.ll
+++ b/llvm/test/Transforms/InstCombine/select-implied.ll
@@ -162,3 +162,39 @@ fpath:
 end:
   ret i32 0
 }
+
+; LHS ==> RHS by definition (true -> true)
+; CHECK-LABEL: @test6
+; CHECK: taken:
+; CHECK-NOT: select
+; CHECK: call void @foo(i32 10)
+define void @test6(i32 %a, i32 %b) {
+  %cmp1 = icmp eq i32 %a, %b
+  br i1 %cmp1, label %taken, label %end
+
+taken:
+  %c = select i1 %cmp1, i32 10, i32 0
+  call void @foo(i32 %c)
+  br label %end
+
+end:
+  ret void
+}
+
+; LHS ==> RHS by definition (false -> false)
+; CHECK-LABEL: @test7
+; CHECK: taken:
+; CHECK-NOT: select
+; CHECK: call void @foo(i32 11)
+define void @test7(i32 %a, i32 %b) {
+  %cmp1 = icmp eq i32 %a, %b
+  br i1 %cmp1, label %end, label %taken
+
+taken:
+  %c = select i1 %cmp1, i32 0, i32 11
+  call void @foo(i32 %c)
+  br label %end
+
+end:
+  ret void
+}