optimize ~(~X >>s Y) --> (X >>s Y), patch by Edmund Grimley

Evans!

llvm-svn: 93884

3 files changed, 47 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index af300fc3577..fa7bb12ff21 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1751,6 +1751,11 @@ Instruction *InstCombiner::visitXor(BinaryOperator &I) {
             return BinaryOperator::CreateOr(NotX, NotY);
           return BinaryOperator::CreateAnd(NotX, NotY);
         }
+
+      } else if (Op0I->getOpcode() == Instruction::AShr) {
+        // ~(~X >>s Y) --> (X >>s Y)
+        if (Value *Op0NotVal = dyn_castNotVal(Op0I->getOperand(0)))
+          return BinaryOperator::CreateAShr(Op0NotVal, Op0I->getOperand(1));
       }
     }
   }
diff --git a/llvm/test/Transforms/InstCombine/idioms.ll b/llvm/test/Transforms/InstCombine/idioms.ll
new file mode 100644
index 00000000000..6b3567fc6e8
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/idioms.ll
@@ -0,0 +1,32 @@
+; RUN: opt -instcombine %s -S | FileCheck %s
+
+; Check that code corresponding to the following C function is
+; simplified into a single ASR operation:
+;
+; int test_asr(int a, int b) {
+;   return a < 0 ? -(-a - 1 >> b) - 1 : a >> b;
+; }
+;
+define i32 @test_asr(i32 %a, i32 %b) {
+entry:
+	%c = icmp slt i32 %a, 0
+	br i1 %c, label %bb2, label %bb3
+
+bb2:
+	%t1 = sub i32 0, %a
+	%not = sub i32 %t1, 1
+	%d = ashr i32 %not, %b
+	%t2 = sub i32 0, %d
+	%not2 = sub i32 %t2, 1
+	br label %bb4
+bb3:
+	%e = ashr i32 %a, %b
+	br label %bb4
+bb4:
+        %f = phi i32 [ %not2, %bb2 ], [ %e, %bb3 ]
+	ret i32 %f
+; CHECK: @test_asr
+; CHECK: bb4:
+; CHECK: %f = ashr i32 %a, %b
+; CHECK: ret i32 %f
+}
diff --git a/llvm/test/Transforms/InstCombine/xor2.ll b/llvm/test/Transforms/InstCombine/xor2.ll
index 23a99158137..de3d65dd8cb 100644
--- a/llvm/test/Transforms/InstCombine/xor2.ll
+++ b/llvm/test/Transforms/InstCombine/xor2.ll
@@ -41,3 +41,13 @@ define i32 @test3(i32 %tmp1) {
   %ov110 = xor i32 %ov31, 153
   ret i32 %ov110
 }
+
+define i32 @test4(i32 %A, i32 %B) {
+	%1 = xor i32 %A, -1
+	%2 = ashr i32 %1, %B
+	%3 = xor i32 %2, -1
+	ret i32 %3
+; CHECK: @test4
+; CHECK: %1 = ashr i32 %A, %B
+; CHECK: ret i32 %1
+}