From 7eb6751ff60673ab6503d7f29cbb7569f5c077be Mon Sep 17 00:00:00 2001
From: Chad Rosier <mcrosier@codeaurora.org>
Date: Tue, 17 Jan 2017 17:23:51 +0000
Subject: [PATCH] [ValueTracking] Extend known bits to understand
 @llvm.bitreverse.

Differential Revision: https://reviews.llvm.org/D28780

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292233 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ValueTracking.cpp                |  5 +++
 .../InstCombine/bitreverse-known-bits.ll      | 34 +++++++++++++++++++
 test/Transforms/InstSimplify/bitreverse.ll    | 31 +++++++++++++++++
 3 files changed, 70 insertions(+)
 create mode 100644 test/Transforms/InstCombine/bitreverse-known-bits.ll
 create mode 100644 test/Transforms/InstSimplify/bitreverse.ll

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 244aa798a9c..d926b3864de 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -1400,6 +1400,11 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
     if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
       switch (II->getIntrinsicID()) {
       default: break;
+      case Intrinsic::bitreverse:
+        computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
+        KnownZero = KnownZero2.reverseBits();
+        KnownOne = KnownOne2.reverseBits();
+        break;
       case Intrinsic::bswap:
         computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
         KnownZero |= KnownZero2.byteSwap();
diff --git a/test/Transforms/InstCombine/bitreverse-known-bits.ll b/test/Transforms/InstCombine/bitreverse-known-bits.ll
new file mode 100644
index 00000000000..b73df77b925
--- /dev/null
+++ b/test/Transforms/InstCombine/bitreverse-known-bits.ll
@@ -0,0 +1,34 @@
+; RUN: opt < %s -S -instcombine | FileCheck %s
+
+declare i32 @llvm.bitreverse.i32(i32)
+
+; CHECK-LABEL: @test1
+; CHECK: ret i1 true
+define i1 @test1(i32 %arg) {
+  %a = or i32 %arg, 4294901760
+  %b = call i32 @llvm.bitreverse.i32(i32 %a)
+  %and = and i32 %b, 65535
+  %res = icmp eq i32 %and, 65535
+  ret i1 %res
+}
+
+; CHECK-LABEL: @test2
+; CHECK: ret i1 true
+define i1 @test2(i32 %arg) {
+  %a = or i32 %arg, 1
+  %b = call i32 @llvm.bitreverse.i32(i32 %a)
+  %c = and i32 %b, 2147483648
+  %d = call i32 @llvm.bitreverse.i32(i32 %c)
+  %res = icmp eq i32 %d, 1
+  ret i1 %res
+}
+
+; CHECK-LABEL: @test3
+; CHECK: ret i1 false
+define i1 @test3(i32 %arg) {
+  %a = or i32 %arg, 65536
+  %b = call i32 @llvm.bitreverse.i32(i32 %a)
+  %and = and i32 %b, 32768
+  %res = icmp eq i32 %and, 0
+  ret i1 %res
+}
diff --git a/test/Transforms/InstSimplify/bitreverse.ll b/test/Transforms/InstSimplify/bitreverse.ll
new file mode 100644
index 00000000000..d87b68831fe
--- /dev/null
+++ b/test/Transforms/InstSimplify/bitreverse.ll
@@ -0,0 +1,31 @@
+; RUN: opt < %s -S -instsimplify | FileCheck %s
+
+declare i32 @llvm.bitreverse.i32(i32)
+
+; CHECK-LABEL: @test1(
+; CHECK: ret i1 false
+define i1 @test1(i32 %arg) {
+  %a = or i32 %arg, 1
+  %b = call i32 @llvm.bitreverse.i32(i32 %a)
+  %res = icmp eq i32 %b, 0
+  ret i1 %res
+}
+
+; CHECK-LABEL: @test2(
+; CHECK: ret i1 false
+define i1 @test2(i32 %arg) {
+  %a = or i32 %arg, 1024
+  %b = call i32 @llvm.bitreverse.i32(i32 %a)
+  %res = icmp eq i32 %b, 0
+  ret i1 %res
+}
+
+; CHECK-LABEL: @test3(
+; CHECK: ret i1 false
+define i1 @test3(i32 %arg) {
+  %a = and i32 %arg, 1
+  %b = call i32 @llvm.bitreverse.i32(i32 %a)
+  %and = and i32 %b, 1
+  %res = icmp eq i32 %and, 1
+  ret i1 %res
+}
-- 
2.40.0