[PATCH] D39004: [ARM] Swap cmp operands for automatic shifts.

[Sam Parker via Phabricator via llvm-commits]

samparker created this revision.
Herald added subscribers: kristof.beyls, javed.absar, aemerson.

Swap the compare operands if the lhs is a shift and the rhs isn't, as in arm and T2 the shift can be performed by the compare for its second operand.


https://reviews.llvm.org/D39004

Files:
  lib/Target/ARM/ARMISelLowering.cpp
  test/CodeGen/ARM/cmp-shift-swap.ll


Index: test/CodeGen/ARM/cmp-shift-swap.ll
===================================================================
--- /dev/null
+++ test/CodeGen/ARM/cmp-shift-swap.ll
@@ -0,0 +1,35 @@
+; RUN: llc -mtriple=thumbv7m %s -o - | FileCheck %s --check-prefix=CHECK-T2
+; RUN: llc -mtriple=armv7 %s -o - | FileCheck %s
+
+; CHECK-LABEL: swap_cmp_shl
+; CHECK: cmp r1, r0, lsl #11
+; CHECK-T2: cmp.w r1, r0, lsl #11
+define arm_aapcscc i32 @swap_cmp_shl(i32 %a, i32 %b) {
+entry:
+  %add = shl i32 %a, 11
+  %cmp = icmp sgt i32 %add, %b
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+; CHECK-LABEL: swap_cmp_lshr
+; CHECK: cmp r1, r0, lsr #11
+; CHECK-T2: cmp.w r1, r0, lsr #11
+define arm_aapcscc i32 @swap_cmp_lshr(i32 %a, i32 %b) {
+entry:
+  %add = lshr i32 %a, 11
+  %cmp = icmp sgt i32 %add, %b
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
+
+; CHECK-LABEL: swap_cmp_ashr
+; CHECK: cmp r1, r0, asr #11
+; CHECK-T2: cmp.w r1, r0, asr #11
+define arm_aapcscc i32 @swap_cmp_ashr(i32 %a, i32 %b) {
+entry:
+  %add = ashr i32 %a, 11
+  %cmp = icmp sgt i32 %add, %b
+  %conv = zext i1 %cmp to i32
+  ret i32 %conv
+}
Index: lib/Target/ARM/ARMISelLowering.cpp
===================================================================
--- lib/Target/ARM/ARMISelLowering.cpp
+++ lib/Target/ARM/ARMISelLowering.cpp
@@ -3821,6 +3821,7 @@
 SDValue ARMTargetLowering::getARMCmp(SDValue LHS, SDValue RHS, ISD::CondCode CC,
                                      SDValue &ARMcc, SelectionDAG &DAG,
                                      const SDLoc &dl) const {
+  bool SwapOperands = false;
   if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(RHS.getNode())) {
     unsigned C = RHSC->getZExtValue();
     if (!isLegalICmpImmediate(C)) {
@@ -3857,9 +3858,17 @@
         break;
       }
     }
-  }
+  } else if ((ARM_AM::getShiftOpcForNode(LHS.getOpcode()) != ARM_AM::no_shift)&&
+             (ARM_AM::getShiftOpcForNode(RHS.getOpcode()) == ARM_AM::no_shift))
+    // In ARM and Thumb-2, the compare instructions can shift their second
+    // operand.
+    SwapOperands = true;
 
   ARMCC::CondCodes CondCode = IntCCToARMCC(CC);
+  if (SwapOperands) {
+    CondCode = ARMCC::getOppositeCondition(CondCode);
+    std::swap(LHS, RHS);
+  }
   ARMISD::NodeType CompareType;
   switch (CondCode) {
   default:


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