[llvm] r298624 - [ARM] Fix computeKnownBits for ARMISD::CMOV

[Pirama Arumuga Nainar via llvm-commits]

Author: pirama
Date: Thu Mar 23 11:47:47 2017
New Revision: 298624

URL: http://llvm.org/viewvc/llvm-project?rev=298624&view=rev
Log:
[ARM] 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

Added:
    llvm/trunk/test/CodeGen/ARM/no-cmov2bfi.ll
Modified:
    llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp

Modified: llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp?rev=298624&r1=298623&r2=298624&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMISelLowering.cpp Thu Mar 23 11:47:47 2017
@@ -11695,8 +11695,8 @@ static void computeKnownBits(SelectionDA
   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;

Added: llvm/trunk/test/CodeGen/ARM/no-cmov2bfi.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/no-cmov2bfi.ll?rev=298624&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/no-cmov2bfi.ll (added)
+++ llvm/trunk/test/CodeGen/ARM/no-cmov2bfi.ll Thu Mar 23 11:47:47 2017
@@ -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
+}