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

Evans!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93884 91177308-0d34-0410-b5e6-96231b3b80d8

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
+}