ARM: fix CodeGen for 64-bit shifts.

One half of the shifts obviously needed conditional selection based on whether
the shift amount is more than 32-bits, but leaving the other half as the
natural shift isn't acceptable either: it's undefined behaviour to shift a
32-bit value by more than 31.

llvm-svn: 287149

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -4893,6 +4893,7 @@ SDValue ARMTargetLowering::LowerShiftRightParts(SDValue Op,
   SDValue ShOpHi = Op.getOperand(1);
   SDValue ShAmt  = Op.getOperand(2);
   SDValue ARMcc;
+  SDValue CCR = DAG.getRegister(ARM::CPSR, MVT::i32);
   unsigned Opc = (Op.getOpcode() == ISD::SRA_PARTS) ? ISD::SRA : ISD::SRL;
 
   assert(Op.getOpcode() == ISD::SRA_PARTS || Op.getOpcode() == ISD::SRL_PARTS);
@@ -4903,15 +4904,23 @@ SDValue ARMTargetLowering::LowerShiftRightParts(SDValue Op,
   SDValue ExtraShAmt = DAG.getNode(ISD::SUB, dl, MVT::i32, ShAmt,
                                    DAG.getConstant(VTBits, dl, MVT::i32));
   SDValue Tmp2 = DAG.getNode(ISD::SHL, dl, VT, ShOpHi, RevShAmt);
-  SDValue FalseVal = DAG.getNode(ISD::OR, dl, VT, Tmp1, Tmp2);
+  SDValue LoSmallShift = DAG.getNode(ISD::OR, dl, VT, Tmp1, Tmp2);
-  SDValue TrueVal = DAG.getNode(Opc, dl, VT, ShOpHi, ExtraShAmt);
+  SDValue LoBigShift = DAG.getNode(Opc, dl, VT, ShOpHi, ExtraShAmt);
+  SDValue CmpLo = getARMCmp(ExtraShAmt, DAG.getConstant(0, dl, MVT::i32),
+                            ISD::SETGE, ARMcc, DAG, dl);
+  SDValue Lo = DAG.getNode(ARMISD::CMOV, dl, VT, LoSmallShift, LoBigShift,
+                           ARMcc, CCR, CmpLo);
 
-  SDValue CCR = DAG.getRegister(ARM::CPSR, MVT::i32);
+
-  SDValue Cmp = getARMCmp(ExtraShAmt, DAG.getConstant(0, dl, MVT::i32),
+  SDValue HiSmallShift = DAG.getNode(Opc, dl, VT, ShOpHi, ShAmt);
-                          ISD::SETGE, ARMcc, DAG, dl);
+  SDValue HiBigShift = Opc == ISD::SRA
-  SDValue Hi = DAG.getNode(Opc, dl, VT, ShOpHi, ShAmt);
+                           ? DAG.getNode(Opc, dl, VT, ShOpHi,
-  SDValue Lo = DAG.getNode(ARMISD::CMOV, dl, VT, FalseVal, TrueVal, ARMcc,
+                                         DAG.getConstant(VTBits - 1, dl, VT))
-                           CCR, Cmp);
+                           : DAG.getConstant(0, dl, VT);
+  SDValue CmpHi = getARMCmp(ExtraShAmt, DAG.getConstant(0, dl, MVT::i32),
+                            ISD::SETGE, ARMcc, DAG, dl);
+  SDValue Hi = DAG.getNode(ARMISD::CMOV, dl, VT, HiSmallShift, HiBigShift,
+                           ARMcc, CCR, CmpHi);
 
   SDValue Ops[2] = { Lo, Hi };
   return DAG.getMergeValues(Ops, dl);
@@ -4929,23 +4938,28 @@ SDValue ARMTargetLowering::LowerShiftLeftParts(SDValue Op,
   SDValue ShOpHi = Op.getOperand(1);
   SDValue ShAmt  = Op.getOperand(2);
   SDValue ARMcc;
+  SDValue CCR = DAG.getRegister(ARM::CPSR, MVT::i32);
 
   assert(Op.getOpcode() == ISD::SHL_PARTS);
   SDValue RevShAmt = DAG.getNode(ISD::SUB, dl, MVT::i32,
                                  DAG.getConstant(VTBits, dl, MVT::i32), ShAmt);
   SDValue Tmp1 = DAG.getNode(ISD::SRL, dl, VT, ShOpLo, RevShAmt);
+  SDValue Tmp2 = DAG.getNode(ISD::SHL, dl, VT, ShOpHi, ShAmt);
+  SDValue HiSmallShift = DAG.getNode(ISD::OR, dl, VT, Tmp1, Tmp2);
+
   SDValue ExtraShAmt = DAG.getNode(ISD::SUB, dl, MVT::i32, ShAmt,
                                    DAG.getConstant(VTBits, dl, MVT::i32));
-  SDValue Tmp2 = DAG.getNode(ISD::SHL, dl, VT, ShOpHi, ShAmt);
+  SDValue HiBigShift = DAG.getNode(ISD::SHL, dl, VT, ShOpLo, ExtraShAmt);
-  SDValue Tmp3 = DAG.getNode(ISD::SHL, dl, VT, ShOpLo, ExtraShAmt);
+  SDValue CmpHi = getARMCmp(ExtraShAmt, DAG.getConstant(0, dl, MVT::i32),
+                            ISD::SETGE, ARMcc, DAG, dl);
+  SDValue Hi = DAG.getNode(ARMISD::CMOV, dl, VT, HiSmallShift, HiBigShift,
+                           ARMcc, CCR, CmpHi);
 
-  SDValue FalseVal = DAG.getNode(ISD::OR, dl, VT, Tmp1, Tmp2);
+  SDValue CmpLo = getARMCmp(ExtraShAmt, DAG.getConstant(0, dl, MVT::i32),
-  SDValue CCR = DAG.getRegister(ARM::CPSR, MVT::i32);
-  SDValue Cmp = getARMCmp(ExtraShAmt, DAG.getConstant(0, dl, MVT::i32),
                           ISD::SETGE, ARMcc, DAG, dl);
-  SDValue Lo = DAG.getNode(ISD::SHL, dl, VT, ShOpLo, ShAmt);
+  SDValue LoSmallShift = DAG.getNode(ISD::SHL, dl, VT, ShOpLo, ShAmt);
-  SDValue Hi = DAG.getNode(ARMISD::CMOV, dl, VT, FalseVal, Tmp3, ARMcc,
+  SDValue Lo = DAG.getNode(ARMISD::CMOV, dl, VT, LoSmallShift,
-                           CCR, Cmp);
+                           DAG.getConstant(0, dl, VT), ARMcc, CCR, CmpLo);
 
   SDValue Ops[2] = { Lo, Hi };
   return DAG.getMergeValues(Ops, dl);

llvm/test/CodeGen/ARM/shift-i64.ll

@@ -0,0 +1,59 @@
+; RUN: llc -mtriple=arm-eabi %s -o - | FileCheck %s
+
+define i64 @test_shl(i64 %val, i64 %amt) {
+; CHECK-LABEL: test_shl:
+  ; First calculate the hi part when the shift amount is small enough that it
+  ; contains components from both halves. It'll be returned in r1 so that's a
+  ; reasonable place for it to end up.
+; CHECK: rsb [[REVERSE_SHIFT:.*]], r2, #32
+; CHECK: lsr [[TMP:.*]], r0, [[REVERSE_SHIFT]]
+; CHECK: orr r1, [[TMP]], r1, lsl r2
+
+  ; Check whether the shift was in fact small (< 32 bits).
+; CHECK: sub [[EXTRA_SHIFT:.*]], r2, #32
+; CHECK: cmp [[EXTRA_SHIFT]], #0
+
+  ; If not, the high part of the answer is just the low part shifted by the
+  ; excess.
+; CHECK: lslge r1, r0, [[EXTRA_SHIFT]]
+
+  ; The low part is either a direct shift (1st inst) or 0. We can reuse the same
+  ; NZCV.
+; CHECK: lsl r0, r0, r2
+; CHECK: movge r0, #0
+
+  %res = shl i64 %val, %amt
+  ret i64 %res
+}
+
+; Explanation for lshr is pretty much the reverse of shl.
+define i64 @test_lshr(i64 %val, i64 %amt) {
+; CHECK-LABEL: test_lshr:
+; CHECK: lsr r0, r0, r2
+; CHECK: rsb [[REVERSE_SHIFT:.*]], r2, #32
+; CHECK: orr r0, r0, r1, lsl [[REVERSE_SHIFT]]
+; CHECK: sub [[EXTRA_SHIFT:.*]], r2, #32
+; CHECK: cmp [[EXTRA_SHIFT]], #0
+; CHECK: lsrge r0, r1, [[EXTRA_SHIFT]]
+; CHECK: lsr r1, r1, r2
+; CHECK: movge r1, #0
+  %res = lshr i64 %val, %amt
+  ret i64 %res
+}
+
+; One minor difference for ashr: the high bits must be "hi >> 31" if the shift
+; amount is large to get the right sign bit.
+define i64 @test_ashr(i64 %val, i64 %amt) {
+; CHECK-LABEL: test_ashr:
+; CHECK: sub [[EXTRA_SHIFT:.*]], r2, #32
+; CHECK: asr [[HI_TMP:.*]], r1, r2
+; CHECK: lsr r0, r0, r2
+; CHECK: rsb [[REVERSE_SHIFT:.*]], r2, #32
+; CHECK: cmp [[EXTRA_SHIFT]], #0
+; CHECK: orr r0, r0, r1, lsl [[REVERSE_SHIFT]]
+; CHECK: asrge [[HI_TMP]], r1, #31
+; CHECK: asrge r0, r1, [[EXTRA_SHIFT]]
+; CHECK: mov r1, [[HI_TMP]]
+  %res = ashr i64 %val, %amt
+  ret i64 %res
+}