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

Gbp-Pq: Name rust-0032-Fix-computeKnownBits-for-ARMISD-CMOV.patch

diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index 3cfcb1e09f0bd4080850a7cb2e329b567ebc0dfd..23c60cf2f59c6e460529aed52b517b643b3b6765 100644 (file)
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -10805,8 +10805,8 @@ 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 (file)
index 0000000..c8b5120
--- /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
+}