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From a6fa10c14649c18d299cddf3e823b032460cb6f5 Mon Sep 17 00:00:00 2001
From: Pirama Arumuga Nainar <pirama@google.com>
Date: Thu, 23 Mar 2017 16:47:47 +0000
Subject: [PATCH] Fix computeKnownBits for ARMISD::CMOV

Summary:
The true and false operands for the CMOV are operands 0 and 1.
ARMISelLowering.cpp::computeKnownBits was looking at operands 1 and 2
instead.  This can cause CMOV instructions to be incorrectly folded into
BFI if value set by the CMOV is another CMOV, whose known bits are
computed incorrectly.

This patch fixes the issue and adds a test case.

Reviewers: kristof.beyls, jmolloy

Subscribers: llvm-commits, aemerson, srhines, rengolin

Differential Revision: https://reviews.llvm.org/D31265

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298624 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/ARM/ARMISelLowering.cpp |  4 ++--
 test/CodeGen/ARM/no-cmov2bfi.ll    | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)
 create mode 100644 test/CodeGen/ARM/no-cmov2bfi.ll

diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 4a227a3cd7b1..cf98e60c0657 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -10806,8 +10806,8 @@ static void computeKnownBits(SelectionDAG &DAG, SDValue Op, APInt &KnownZero,
   if (Op.getOpcode() == ARMISD::CMOV) {
     APInt KZ2(KnownZero.getBitWidth(), 0);
     APInt KO2(KnownOne.getBitWidth(), 0);
-    computeKnownBits(DAG, Op.getOperand(1), KnownZero, KnownOne);
-    computeKnownBits(DAG, Op.getOperand(2), KZ2, KO2);
+    computeKnownBits(DAG, Op.getOperand(0), KnownZero, KnownOne);
+    computeKnownBits(DAG, Op.getOperand(1), KZ2, KO2);
 
     KnownZero &= KZ2;
     KnownOne &= KO2;
diff --git a/test/CodeGen/ARM/no-cmov2bfi.ll b/test/CodeGen/ARM/no-cmov2bfi.ll
new file mode 100644
index 000000000000..c8b512048905
--- /dev/null
+++ b/test/CodeGen/ARM/no-cmov2bfi.ll
@@ -0,0 +1,19 @@
+; RUN: llc < %s -mtriple=thumbv7 | FileCheck --check-prefix=CHECK-NOBFI %s
+
+declare zeroext i1 @dummy()
+
+define i8 @test(i8 %a1, i1 %c) {
+; CHECK-NOBFI-NOT: bfi
+; CHECK-NOBFI: bl      dummy
+; CHECK-NOBFI: cmp     r0, #0
+; CHECK-NOBFI: it      ne
+; CHECK-NOBFI: orrne   [[REG:r[0-9]+]], [[REG]], #8
+; CHECK-NOBFI: mov     r0, [[REG]]
+
+  %1 = and i8 %a1, -9
+  %2 = select i1 %c, i8 %1, i8 %a1
+  %3 = tail call zeroext i1 @dummy()
+  %4 = or i8 %2, 8
+  %ret = select i1 %3, i8 %4, i8 %2
+  ret i8 %ret
+}
-- 
2.9.3