Do not expand SDIV when compiling for minimum code size

[SjoerdMeijer]

Summary

Do not expand SDIV when compiling for minimum code size

[bkramer]

lgtm

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

SDValue DAGCombiner::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
   return TLI.SimplifySetCC(VT, N0, N1, Cond, foldBooleans, DagCombineInfo, DL);
 }
 
 /// Given an ISD::SDIV node expressing a divide by constant, return
 /// a DAG expression to select that will generate the same value by multiplying
 /// by a magic number.
 /// Ref: "Hacker's Delight" or "The PowerPC Compiler Writer's Guide".
 SDValue DAGCombiner::BuildSDIV(SDNode *N) {
+  // when optimising for minimum size, we don't want to expand a div to a mul
+  // and a shift.
+  if (DAG.getMachineFunction().getFunction()->optForMinSize())
+    return SDValue();
+
   ConstantSDNode *C = isConstOrConstSplat(N->getOperand(1));
   if (!C)
     return SDValue();
 
   // Avoid division by zero.
   if (C->isNullValue())
     return SDValue();
 

test/CodeGen/ARM/urem-opt-size.ll

-; When optimising for minimum size, we don't want to expand a udiv to a mul
-; and a shift sequence. As a result, the urem instruction will not be
+; When optimising for minimum size, we don't want to expand a div to a mul
+; and a shift sequence. As a result, the urem instruction e.g. will not be
 ; expanded to a sequence of umull, lsrs, muls and sub instructions, but
 ; just a call to __aeabi_uidivmod.
 ;
 ; RUN: llc -mtriple=armv7a-eabi -mattr=-neon -verify-machineinstrs %s -o - | FileCheck %s
 
 target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
 target triple = "thumbv7m-arm-none-eabi"
 
-define i32 @foo() local_unnamed_addr #0 {
+define i32 @foo1() local_unnamed_addr #0 {
 entry:
-; CHECK-LABEL: foo:
+; CHECK-LABEL: foo1:
+; CHECK:__aeabi_idiv
+; CHECK-NOT: smmul
+  %call = tail call i32 bitcast (i32 (...)* @GetValue to i32 ()*)()
+  %div = sdiv i32 %call, 1000000
+  ret i32 %div
+}
+
+define i32 @foo2() local_unnamed_addr #0 {
+entry:
+; CHECK-LABEL: foo2:
+; CHECK: __aeabi_uidiv
+; CHECK-NOT: umull
+  %call = tail call i32 bitcast (i32 (...)* @GetValue to i32 ()*)()
+  %div = udiv i32 %call, 1000000
+  ret i32 %div
+}
+
+define i32 @foo3() local_unnamed_addr #0 {
+entry:
+; CHECK-LABEL: foo3:
 ; CHECK: __aeabi_uidivmod
 ; CHECK-NOT: umull
   %call = tail call i32 bitcast (i32 (...)* @GetValue to i32 ()*)()
   %rem = urem i32 %call, 1000000
   %cmp = icmp eq i32 %rem, 0
   %conv = zext i1 %cmp to i32
   ret i32 %conv
 }
 
 declare i32 @GetValue(...) local_unnamed_addr
 
 attributes #0 = { minsize nounwind optsize }